These reasons alone have permitted some to call the squat the âKing of all Exercises. .... of a line connecting the anterior superior iliac spine to the center of the patella and another line ...... Clin Biomech (Bristol, Avon), 1996. 11(2): p. 81-. 89.
THE EFFECT OF SQUAT LOAD AND DEPTH ON PATELLOFEMORAL JOINT KINETICS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Joshua A. Cotter, M.A. *****
The Ohio State University 2009
Dissertation Committee: Professor Steven T. Devor, Adviser Approved by Professor Ajit M. Chaudhari Professor Christopher C. Kaeding Professor Timothy E. Kirby
Adviser College of Education and Human Ecology
Copyright by Joshua Allan Cotter 2009
ABSTRACT
The squat exercise is prescribed in a wide variety of situations ranging from performance enhancement to rehabilitation. Although widely used, there is dispute among professionals as to what depth should be prescribed. With patellofemoral pain being one of the most common disorders of the knee, it is important to better understand the patellofemoral forces at differing loads and depths of the squat exercise. In general, decreasing loads are needed when depth of the squat is increased. It was hypothesized that the decreased loads often seen with increasing depths would result in no difference in patellofemoral joint reaction forces (PFJRF). A secondary purpose of this study was to find a relationship between squat one repetition max (1RM) and depth to help predict squat loads at deep depths from one repetition max achieved at a higher depth. Sixteen males with no previous leg surgeries and at least one year of experience resistance training participated in the study. Subjects were visually screened before participation to ensure adequate depth could be achieved. One repetition max testing was conducted at three different depths of above parallel (~ 90o), parallel (~110o), and below parallel (~135o). Subsequently, motion capture testing at the same depths under unloaded, 50% 1RM, and 85% 1RM conditions was performed. A total of 9 trials were completed utilizing the three depths and loads. An addition 4 trials were completed at ii
the parallel and above parallel depths using the below parallel 50% and 85% 1RM loads to assess the effect of depth on PFJRF with constant loads. Post-test analysis revealed that peak knee moments and PFJRF were significantly different at all depths with a %1RM and constant load (p < 0.05). Peak knee moments and PFJRF were also significantly different with increasing loads for each squat depth (p < 0.05). Unloaded parallel and below parallel squats were not significantly different. One repetition max loads were significantly different at all levels (p < 0.05). A regression equation was developed to predict both parallel (R2 = 0.764) and below parallel (R2 = 0.641) from a 90° above parallel squat. The main finding of this study was that typical decreases in weights used with increasing depths are not enough to offset the increases in PFJRF typically seen with increasing knee flexion. Interpretation of these results should be done with caution as there are many other variables involved in the squat exercise. These results, along with a proper individualized assessment, may better help in the utilization of the squat exercise in rehabilitation and training programs.
iii
Dedicated to my grandparents
iv
ACKNOWLEDGEMENTS
I humbly acknowledge that this work, as well as my education leading up to this point, would not be possible without the countless support I received from family, friends, and colleagues. Without them, I would not have been able to complete this project. I first would like to thank my grandparents. They have raised me since I first entered this world and have guided me every step of the way. I honestly and truly do not know where I would be today if it wasn’t for them. I am honored, proud, and thankful that they have always been there for me. Whether I have good news or bad, they are always there to provide support and understanding. I can never thank them enough for everything they have done for me. I would also like to thank Dr. Steven Devor who has been there since I first started my education in this program. Although the road was definitely rocky at times, he still believed I could finish what I put my mind to regardless of how doubtful I appeared to be at the time. I am also very thankful to have had Dr. Ajit Chaudhari guide me through the ways of biomechanics. He was very understanding and patient in teaching me what I needed to know. I would also like to thank Dr. Christopher Kaeding for his conversations that sparked new thoughts and ideas that I will continue to pursue in v
the future. Finally, Dr. Timothy Kirby has provided much wisdom along my path to graduation along with a kind willingness to always help out when in need. I am also very thankful to have a great core of friends that were there to support me throughout this project. I would specifically like to thank Aman Khaira, Billy Hartmann, Alisa Blazek, Justin Dials, and Cory Sheadler for listening to more than their fair share of my complaining. No one though can take more credit for listening to my rants and raves than my girlfriend Carolyn Owings. She was unwavering in her support and understanding throughout this project. I would also like to thank a new friend, Steve Jamison, who was indispensible at allowing my research to take place. There were many other individuals that played a part in allowing this research to happen. Kay Yeager has always provided a happy shining face along with a willingness to help in any way possible. Brooke Diller, Shannon Donovan, Brian Polzner, Matt Kretovics, and several other undergraduate students provided much needed assistance. Steve’s Dad even made a special trip to provide his electrical expertise for the light curtain setup. Finally, if it wasn’t for the curiosity and drive of my subjects who volunteered their time for nothing more than knowledge and experience, this study would not have been completed.
vi
VITA July 23, 1980 . . . . . . . . . . . . . . . . . . . . . . Born – New Philadelphia, OH 2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.S.B.A. Management Information Systems, The Ohio State University. 2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M.A. Health and Exercise Science, The Ohio State University. 2004-2009 . . . . . . . . . . . . . . . . . . . . . . . . . Graduate teaching and research associate, The Ohio State University
RESEARCH INVOLVEMENT 1.
Focht, BA., Garver M., and Cotter, JA. Perceived exertion during acute resistance exercise performed at self-selected and imposed loads in trained women. Presented at the ACSM Annual Meeting. 2009. Seattle, WA.
2.
Cotter, JA. Anthropometric, strength, and flexibility characteristics of preadolescent competitive gymnasts: seven case studies. 2004: Master’s Thesis.
FIELDS OF STUDY Major Field: Education
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TABLE OF CONTENTS
Page Abstract .............................................................................................................................. ii Dedication ......................................................................................................................... iv Acknowledgements .............................................................................................................v Vita ................................................................................................................................... vii List of Tables ......................................................................................................................x List of Figures .................................................................................................................. xii Chapters: 1. Introduction Preface .....................................................................................................................1 The squat exercise ...................................................................................................3 Patellofemoral pain .................................................................................................6 Objectives .............................................................................................................10 Stated hypotheses and findings .............................................................................10 2. Methods Research design ....................................................................................................13 Sample ...................................................................................................................14 Pre-study inclusion criteria ...................................................................................15 Pre-study exclusion criteria ...................................................................................15 Procedures .............................................................................................................16 One repetition max testing ....................................................................................16 Motion capture testing ..........................................................................................19 One repetition max relationships ..........................................................................26 Patellofemoral joint kinetics .................................................................................26 3. Results Population .............................................................................................................28 Squat one repetition max and depth ......................................................................29 viii
Peak external knee flexion moments ....................................................................31 Patellofemoral joint reaction force ........................................................................36 4. Discussion Main findings ........................................................................................................44 Patellofemoral joint reaction force model .............................................................47 Limitations ............................................................................................................50 Practical applications ............................................................................................55 Conclusions ...........................................................................................................58 References .........................................................................................................................59 Appendix A: IRB approval letter ......................................................................................67 Appendix B: IRB application ............................................................................................69 Appendix C: Recruitment flyer .........................................................................................83 Appendix D: Consent form ...............................................................................................85 Appendix E: HIPAA form ................................................................................................93 Appendix F: One repetition max collection worksheet ....................................................97 Appendix G: Data collection worksheet ...........................................................................99 Appendix H: Squat trial worksheet .................................................................................101 Appendix I: Raw subject data .........................................................................................103
ix
LIST OF TABLES Table
Page
2.1
Percentage one repetition max trials ...................................................................14
2.2
Constant load trials .............................................................................................14
3.1
Subject demographics .........................................................................................28
I.1
Baseline demographics and one repetition max data ........................................104
I.2
Peak tibiofemoral angles for the 90° above parallel squat trials.......................105
I.3
Peak tibiofemoral angles for the 110° parallel squat trials ...............................106
I.4
Peak tibiofemoral angles for the 135° below parallel squat trials ....................107
I.5
Peak external knee flexion moments (Nm) for the 90° above parallel squat trials. ...........................................................................................................................108
I.6
Peak external knee flexion moments (Nm) for the 110° parallel squat trials ...109
I.7
Peak external knee flexion moments (Nm) for the 135° below parallel squat trials ...........................................................................................................................110
I.8
Angles at peak moments for 90° above parallel squat trials .............................111
I.9
Angles at peak moments for 110° parallel squat trials .....................................112
I.10
Angles at peak moments for 135° below parallel squat trials...........................113
I.11
Effective quadriceps lever arms (cm) for the 90° above parallel squat trials ...114
I.12
Effective quadriceps lever arms (cm) for the 110° parallel squat trials ............115
I.13
Effective quadriceps lever arms (cm) for the 135° below parallel squat trials ....... ...........................................................................................................................116 x
I.14
Quadriceps force (N) for the 90° above parallel squat trials ............................117
I.15
Quadriceps force (N) for the 110° parallel squat trials .....................................118
I.16
Quadriceps force (N) for the 135° below parallel squat trials ..........................119
I.17
Constant k (JRFpf / Fq) for the 90° above parallel squat trials ........................120
I.18
Constant k (JRFpf / Fq) for the 110° parallel squat trials .................................121
I.19
Constant k (JRFpf / Fq) for the 135° below parallel squat trials ......................122
I.20
Patellofemoral joint reaction forces (N) for the 90° above parallel squat trials ..... ...........................................................................................................................123
I.21
Patellofemoral joint reaction forces (N) for the 110° parallel squat trials ........124
I.22
Patellofemoral joint reaction forces (N) for the 135° below parallel squat trials ...........................................................................................................................125
I.23
Patellofemoral joint reaction forces (x BW) for the 90° above parallel squat trials ...........................................................................................................................126
I.24
Patellofemoral joint reaction forces (x BW) for the 110° parallel squat trials ....... ...........................................................................................................................127
I.25
Patellofemoral joint reaction forces (x BW) for the 135° below parallel squat trials ...........................................................................................................................128
xi
LIST OF FIGURES Table 2.1
Page
Light curtain setup .................................................................................................17
2.2 Squat depth criteria ................................................................................................18 2.3
Marker placement ..................................................................................................21
2.4 Marker removal ......................................................................................................23 2.5 Hip joint center ......................................................................................................25 3.1
One repetition max values .....................................................................................29
3.2 Relationship between one repetition max at a 90° above parallel squat and a 110° parallel squat ..........................................................................................................30 3.3 Relationship between one repetition max at a 90° above parallel squat and a 110° parallel squat ..........................................................................................................31 3.4 Peak external knee flexion moments with constant loads .....................................33 3.5 Peak external knee flexion moments with %1RM loads .......................................35 3.6 Patellofemoral joint reaction force with constant loads .........................................37 3.7 Patellofemoral joint reaction force normalized by body weight with constant loads ................................................................................................................................39 3.8 Patellofemoral joint reaction force with %1RM loads ..........................................41 3.9 Patellofemoral joint reaction force normalized by body weight with %1RM loads.. ................................................................................................................................43 4.1
Moment arm of the rectus femoris and the effective quadriceps lever arm...........49 xii
CHAPTER 1
INTRODUCTION
Preface The squat exercise is an exercise that is utilized in a wide variety of environments ranging from rehabilitation to strength and conditioning programs. The use of the squat exercise stems from its similarity to many functional activities of daily living and athletic movements along with its multi-joint involvement incorporating many large muscle groups of the body working in conjunction. The squat exercise has been said to increase ligament and tendon strength and bone density, increase development, strength, speed, and power of the lower back, hip and knee musculature, and improve neuromuscular efficiency [1]. These reasons alone have permitted some to call the squat the “King of all Exercises.” It is no surprise then that many strength and conditioning coaches have used it in their programs for performance enhancement [2]. Although widely used, the squat is not without controversy. Many health professionals believe that the squat exercise may elicit high forces on the knee and should potentially be performed with limited knee flexion [3, 4] The American College of Sports Medicine recommends that when engaging in resistance training, the apparently healthy adult should “perform every exercise through a 1
full range of motion [5]. Working through a full range of motion will allow strength adaptation to occur at all ranges of motion which may reduce injury potential in those ranges. In addition, utilizing the full range of motion for exercises maintains flexibility for joint integrity. Some coaches even use the deep squat as an assessment tool for lower body flexibility and symmetry of movement [6]. Even though many health professionals agree that working through full range of motion is important, the knee joint, and specifically the squat, are often seen as exceptions to the rule. Training with the squat exercise is not the only way the squat is utilized. Many activities of daily living also require a squatting type movement. Tasks such as sitting or rising from a chair, picking something off of the floor, and gardening are just a few tasks that may require a squatting movement. In fact, much of the world’s population requires the use of a deep squat when toileting whereby one squats over a hole or bowl embedded in the floor [7]. Squatting is also practiced in many Asian and Middle-Eastern countries for socializing, working, and religious acts. In people with knee replacements, 50% of a sample of 176 patients engaged in squatting activities [8]. This chapter will provide the necessary framework for the following research experiment. Relevant background information and rationale will be provided concerning the efficacy of utilizing the squat exercise along with the potential relevant causes of patellofemoral pain.
2
The Squat Exercise Many athletes and coaches believe that the squat exercise enhances athletic performance and minimizes injury potential [9]. By utilizing the musculature about the knee, hip, and core, the squat exercise targets many of the large muscle groups used in running, jumping, lifting, and sporting movements. In addition, many daily functional tasks as well as sporting movements require the coordination of several different muscles therefore making the squat an effective exercise as it recruits multiple muscle groups in a single movement [10-12]. Although there is a large amount of literature on the squat exercise, there is difficulty in its interpretation due to the wide assortment of squat variations available. In addition to the traditional back squat, there are front squats, overhead squats, one-legged squats, squats with the heels off the ground, hack squats, and smith machine squats just to name a few. Within the back squat alone, many variables can be altered to achieve different training effects. Stance width, foot orientation, bar placement, depth and load can all be altered. The following paragraphs will briefly discuss these variables in further depth to better understand how the squat exercise influences training outcomes. From this point forward, the term “squat” will be used to denote the back squat exercise. When any other version of the squat exercise is referred to, it will include a description (i.e. front squat). Stance width and foot orientation is widely variable with the squat exercise. Stance width ranges from near shoulder width to that of double shoulder width whereas common foot orientation includes either toes pointing straight forward or turned outwards 3
to varying degrees. Some coaches believe that specific muscle groups can be isolated by varying stance widths and foot orientations. In general, findings show that there is no difference between stance widths and EMG activity in different thigh muscles [3, 13, 14]. Escamilla et. al. [3] though found that the narrow stance squat increases gastrocnemius activation while others have found increases in gluteus maximus, biceps femoris, and adductor longus with a wide versus narrow stance [13, 14]. In regards to foot orientation, no change in EMG activity was found with varying degrees of foot position [3, 15, 16]. According to these findings, it is preferable to use a comfortable stance while performing the squat considering there is very little difference in muscle recruitment with varying stance widths and foot placement. Bar placement can be utilized in two different positions when performing the back squat exercise. In the Olympic style of squatting, the bar is placed high on the trapezius just below the spinous process of the C7 vertebra and often utilizes a narrower stance whereas a powerlifting style utilizes a lower bar placement across the spine of the scapula and is generally with a wider stance [17]. Coaches generally believe that the high bar placement incorporates a balanced utilization between the anterior and posterior musculature of the thigh whereas the low bar placement emphasizes more of the posterior musculature. Wretenberg [17] found that only the rectus femoris EMG activity was greater in powerlifters versus weightlifters while performing both the parallel and deep squat. Further research should be conducted to find the different training responses that occur with varying bar placements.
4
Although much debate surrounds the topic of what depth one should use when practicing the squat, there is little research available at this time. Caterisano [18] analyzed EMG data from the vastus medialis, vastus lateralis, biceps femoris, and gluteus maximus finding that only the relative contribution of the gluteus maximus increased with increasing depth in the squat. This is in contrast to the belief many coaches hold that deeper squats increase utilization of the vastus medialis oblique along with the hamstring muscle group. Caterisano’s study only utilized weights that consisted of 100125% bodyweight which is significantly less than what many people typically squat to achieve training effects. Increased loads may change EMG activity at differing depths of squats. McCaw [13] found increasing EMG activity of the quadriceps muscle group, adductor longus, and gluteus maximus by increasing parallel squat loads from 60% 1RM to 75% 1RM. Concerns about knee health influence practical advice as to what depth should be achieved while squatting. Controversy began concerning squat depth with a study introduced by Klein [19]. Klein built a device to measure medial and lateral ligament laxity in the knee. His findings indicated greater MCL and LCL instability in weightlifters compared to controls and concluded that deep squats increased instability at the knee. Steiner [20] used the same device as Klein’s and found no difference in knee laxity after a bout of squatting by powerlifters. In contrast, he found significant changes in knee laxity following 90 minutes of basketball play and with recreational runners after a 10km race. In a more comprehensive study, Chandler [21] examined the effects of an 8 week training program including above parallel and below parallel squats finding no 5
effect of squat training on knee laxity. He also went on to compare powerlifters and weightlifters to a control group and found that both powerlifters and weightlifters were actually tighter than controls in several knee laxity tests. An additional concern of knee health is that of patellofemoral joint reaction force (PFJRF), which is potentially related to patellofemoral joint pain through its mechanical stimulus that may cause deterioration of the articular cartilage and subsequent subchondral bone degeneration [22]. It is generally accepted that increased PFJRF is coupled with increasing knee flexion angles. Wallace [23] looked at PFJRF during the descent and ascent phases of the squat exercise to 90˚. It was found that PFJRF increased with increasing knee flexion mirroring the increases found in net peak knee extensor moments. The addition of 35% body weight increased PFJRF up to 45% of the unloaded trials. In a similar study, Salem [24] examined five intercollegiate female athletes squatting to depths of 70˚, 90˚, and 110˚ utilizing 85% of their 1 repetition max (1RM). No differences were found in net peak knee extensor moments or PFJRF at the three depths. In contrast, Dahlkvist [25] generally found increasing PFJRF as greater depth was achieved in an unconventional squat where the heels do not remain on the ground. It is clear that much of the difficulty in interpretation of the current research relating to the squat exercise is in the large amount of variation found in the techniques and loads utilized.
Patellofemoral Pain Patellofemoral pain syndrome (PFPS) is considered one of the most common disorders of the knee, accounting for nearly 30% of all knee injuries treated in sports 6
medicine clinics influencing both athletes and non-athletes alike [22, 26, 27]. Incidence rates are as high as 10% in young female athletes and 7% in young male athletes [28] which account for 33% of all knee injuries in female athletes and 18% of all knee injuries in male athletes [29]. Unfortunately there is not a single cause of PFPS but rather a complex combination of potential risk factors leading to PFPS. Risk factors such as static malalignment, dynamic malalignment, overuse, and muscular dysfunction as well as utilizing improper training equipment and environments all seem to play a role in PFPS. Static malalignment includes dysfunctions while the patient is not moving. A common link to patellofemoral pain is the Q angle or the angle formed by the intersection of a line connecting the anterior superior iliac spine to the center of the patella and another line connecting the tibial tuberosity to the center of the patella. A greater Q angle is theorized to increase lateral forces on the patella which may therefore cause improper patellar tracking [30]. Factors thought to lead to increased Q angles include femoral anteversion, genu valgum and external tibial torsion. Although females typically have greater Q angles and higher incidences of PFPS than males, there are inconsistent findings linking Q angles to PFPS [22, 27]. In addition to the Q angle, hyperpronation of the foot may be a causative factor involved in PFPS in which limitations to tibial external rotation leads to femur internal rotation and therefore potentially more lateral patellar forces [31, 32]. Dynamic malalignment, or malalignment seen with movement, may or may not be seen with concomitant static malalignment. This can include excessive contralateral 7
hip drop, hip adduction and internal rotation, knee abduction, and tibial external rotation and hyperpronation when patients perform a single-leg squat. Because this movement pattern has been linked to PFPS, the concept of improper femur movement, rather than patellar movement, may contribute to PFPS [27]. The underlying factors relating to both static and dynamic malalignment may be a result of muscle dysfunction. Weak hip abductors and external rotators as well as the gluteus medius and core musculature all lead to potential femur and pelvic malalignment and therefore have potential for causing PFPS [27, 33, 34]. In addition, some investigators believe that quadriceps weakness may be the single most important risk factor referring to PFPS [22]. This weakness may be a result of underdeveloped musculature or inhibited neuromuscular control. Because the vastus medialis oblique (VMO) functions to track the patella medially, its importance has been duly noted by investigators. Some research suggests that those with PFPS show significantly more patellar lateralization [35] which may be combated with increased VMO strength. Other studies though have been unable to find an association between VMO and vastus lateralis imbalance or neuromuscular control and PFPS [36-42]. Although conflicting evidence exists, there is strong evidence that quadriceps weakness plays a role in PFPS [22]. There are a multitude of treatment options available for those with patellofemoral pain. Physical therapy is an effective means for dealing with PFPS and often utilizes exercises to help strengthen both the quadriceps and gluteal musculature. Therapists have utilized both open and closed kinetic chain exercises with merit being attributed to both types of approaches. Although open kinetic chain exercises such as the knee 8
extension isolate the quadriceps musculature, some have reported exacerbated symptoms when utilized with patellofemoral pain patients [43, 44]. In addition, closed kinetic chain exercises have been deemed more functional with their closer similarity to functional and sporting movements. This functionality includes a coordinated action of the ankle, hip and knee joints, normal proprioceptive input, muscular cocontraction, tibiofemoral compression forces, and decreased tibial translation [12, 44, 45]. Witvrouw [46] compared 5 weeks of either only open kinetic chain or closed kinetic chain exercises in the non-operative management of PFPS. Although both groups experienced statistically significant decreases in pain and increases in functional performance, the closed kinetic chain group demonstrated more functional benefits along with less locking of the knee, clicking sensations, and pain during isokinetic testing and at night. There were also no differences during a 5 year follow-up between both groups on measures of subjective and functional outcomes [47]. Specificity of training should not be ignored when prescribing exercise for PFPS patients. Augustsson [48] found that healthy subjects training with the barbell squat had significantly greater increases in both a squat 3RM and jump test compared to the open kinetic trained group. Although not directly affecting PFPS, it should also be noted that open kinetic chain exercises tend to produce significantly more anterior displacement of the tibia than closed kinetic chain exercises which may place strain on the ACL [49, 50]. Knowledge of these issues may not only help rehabilitation but also prevention of knee injuries.
9
Objectives 1. Determine the relationship between squat depth and 1RM. 2. Determine the effect of squat depth on peak knee flexion moments given a constant load. 3. Determine the effect of squat depth on peak knee flexion moments given a %1RM. 4. Determine the effect of load on peak knee flexion moments at a given depth. 5. Determine the effect of squat depth on patellofemoral joint reaction force given a constant load. 6. Determine the effect of squat depth on patellofemoral joint reaction force given a %1RM. 7. Determine the effect of load on patellofemoral joint reaction force at a given depth.
Stated Hypotheses and Findings 1. Back squat 1RM load will decrease with increased depth. a. We support this hypothesis after finding that back squat 1RM decreased as depth was increased. 2. Peak knee flexion moments will increase with increased depth given a constant load.
10
a. We support this hypothesis after finding that peak knee flexion moments increased with increased depth at all loads consisting of unloaded, 50% of 135° 1RM and 85% of 135° 1RM. 3. Peak knee flexion moments will not change with increasing depth given a %1RM. a. Our findings do not support this hypothesis. Peak knee flexion moments increased with increasing depth at loads of 50% 1RM and 85% 1RM for each depth. 4. Peak knee flexion moments will increase with increased loads at a given depth. a. We support this hypothesis after finding that at each respective depth, increased load caused increased peak knee flexion moments. 5. Patellofemoral joint reaction force will increase with increased depth given a constant load. a. We partially support this hypothesis after finding that PFJRF increased with increased depth at loads consisting of unloaded, 50% of 135° 1RM and 85% of 135° 1RM except for the unloaded 110° parallel squat and 135° below parallel squat in which there was no difference. 6. Patellofemoral joint reaction force will not change with increasing depth given a %1RM. a. Our findings do not support this hypothesis. PFJRF increased with increasing depth at loads of 50% 1RM and 85% 1RM for each depth. 7. Patellofemoral joint reaction force will increase with increased load.
11
a. We support this hypothesis after finding that at each respective depth, increased load caused increased PFJRF.
12
CHAPTER 2
METHODS
Research Design This study compared the effects of load and depth on patellofemoral joint kinetics during the back squat exercise. This design utilized a one-way ANOVA with repeated measures to compare peak knee flexion moments and patellofemoral joint reaction forces across either the three squatting depths or loads. Main effects were compared utilizing a Bonferroni confidence interval adjustment. A 0.05 level of type I error rate was used to determine statistical significance. Microsoft Excel 2007 (Microsoft Corporation, Redmond, WA) and SPSS Version 17.0 (SPSS Inc., Chicago, IL) software were used for all analyses. Loads consisting of unloaded, 50% 1RM, and 85% 1RM were chosen as representative of typical loads used for both training and rehabilitation. Squatting with no load is often seen when rehabilitating not only patients with patellofemoral pain but also patients with other knee injuries such as ACL reconstruction. When training for power development, loads can be seen as high as 50% 1RM [51, 52] whereas when training for strength and hypertrophy, 85% 1RM is typically used [53, 54]. Depths of 13
above parallel, parallel, and below parallel were chosen as these are all recommended depths suggested for training. These depths correspond approximately to 90°, 110˚ and 135˚ of knee flexion respectively. Trials consisted of combinations of the above squat loads and depth to achieve 9 trials (table 2.1). In addition, the 135˚ 50% and 135˚ 85% 1RM loads were repeated at the 90˚ and 110˚ depths to investigate the effect of constant loads (table 2.2). The total number of squat trials tested was 13.
Above Parallel - 90˚ Unloaded 50% 1RM 85% 1RM
Parallel - 110˚ Unloaded 50% 1RM 85% 1RM
Below Parallel - 135˚ Unloaded 50% 1RM 85% 1RM
Table 2.1 – Percentage one repetition max loads.
Above Parallel - 90˚ Unloaded 50% 135˚ 1RM 85% 135˚ 1RM
Parallel - 110˚ Unloaded 50% 135˚ 1RM 85% 135˚ 1RM
Below Parallel - 135˚ Unloaded 50% 1RM 85% 1RM
Table 2.2 – Constant loads. Bolded items indicate addition trials in addition to the trials labeled in Table 2.1
Sample Subject selection was a convenience sample of individuals recruited at The Ohio State University and surrounding communities. A priori power analysis calculation was conducted using G*Power 3.0.10 [55]. To achieve a power of 0.80, with a large effect 14
size (0.75), the number of subjects needed to find a significant difference (alpha ≤ 0.05) was 16. Recruitment was done by the posting of flyers at the university’s recreational facilities as well as commercial gyms in the surrounding communities.
Pre-study Inclusion Criteria 1.
Male
2.
Between the ages of 18 – 59
3.
> 1 year of consistent resistance training which includes squatting
4.
Individuals with the ability to squat to a full depth in which the hamstrings come into contact with the thighs
Pre-study Exclusion Criteria 1.
Individuals without any previous ACL tears, other ligament tears, tendon tears, muscle tears, or meniscus tear in either lower limb
2.
Individuals without any previous surgeries to either lower limb
Women are excluded from the study due to the difference in kinematics that females possess compared to males [56]. Informed consent (Appendix D) was obtained from all subjects. The protocol was approved through The Ohio State University Institutional Review Board prior to study commencement.
15
Procedures Two visits were required for each subject for this study. The first session involved one repetition max testing in which the one repetition max for each of the specified depths was found. The second session was scheduled at least 24 hours but no longer than one week following 1RM testing.
One Repetition Max Testing One repetition max testing was performed in the OSU Sports Biomechanics Laboratory. Before testing began, the subject’s height was measured. Following the measurement a questionnaire regarding previous squat history was performed orally by the investigator (Appendix G). The protocol for 1RM testing followed the recommendations set by the National Strength and Conditioning Association [57]. The subject was instructed to perform their normal warm-up that is typically done before squatting. After the subject was warmed up, three different height measurements corresponding to the three different squat depths were measured. The measured depths were recorded on two stands which controlled the height of a light curtain (Banner Engineering Corp., Minneapolis, MN). The light curtain is a device that senses any change in light that occurs between the curtain. When the curtain light is triggered, a signal to a light that is positioned in front of the subject will go off for one second. After one second, the light will turn back on signaling the subject to rise out of the squat. This setup was used to control the depth of the subject as well as limit any bouncing or inconsistencies in the amount of time spent in the bottom position. A button is pressed 16
that initiates the process and turns on the light informing the subject that they may begin the trial. Once the achieved depth was attained, the light would go off for one second in which the subject remains in the bottom position. The subject would rise back to a full stand once the light came back on (Figure 2.1). The above parallel squat depth was determined by measuring 90˚ of knee flexion using a goniometer placed at the knee.
Figure 2.1: Light curtain setup.
The parallel depth was determined when the subject’s inguinal crease fell just below the proximal portion of the patella. The below parallel depth was determined when the subject sat fully in a squat position where the hamstrings came into contact with the calves (Figure 2.2). Subjects were instructed to take a natural stance. Stance width and foot orientation were not controlled by the investigators. All squat testing utilized a TDS 17
pro gun rack (TDS Fitness Equipment, Elmira, NY) and a standard barbell (22 kg) and plates. Unloaded trials consisted of subjects squatting with a PVC pipe on their back simulating a barbell.
Figure 2.2: Squat depth criteria.
Once the subject was fully warmed up, the 1RM for the below parallel squat was attempted first. This level was done first as lighter weights are typically used at deeper depths of the squat. The subject was allowed as much time as needed for rest in between sets with a minimum of one minute. It has been shown that one minute intervals have been sufficient for recovery between 1RM back squat attempts [58]. Once the below parallel 1RM was found, the procedure was repeated for the remaining two levels. 18
Following the 1RM testing, the subject scheduled the 2nd session within the following 7 days but no less than 24 hours.
Motion Capture Testing Motion capture testing was conducted in the OSU Sports Biomechanics Laboratory. The first steps of preparation began with the subject wearing the correct attire. Subjects were required to wear a pair of running shorts, low cut shoes and socks that allow the medial and lateral malleolus to be palpated, and either wear no shirt or one that has a low cut neck. Anthropometric measurements were then taken with the subject standing. Knee width was measured medio-laterally across the flexion line of the knee axis. Ankle width was measured medio-laterally across the malleoli. Retro-reflective markers were then attached to the subject’s legs with two-sided adhesive tape utilizing a modified Point-Cluster Technique (PCT) [59, 60]. The modification was the inclusion of a marker placed at the manubrium as well as two markers placed on the iliac spine between each posterior superior iliac spine and the most superior portion of the iliac crest. Anatomical landmarks for the placement of markers consisted of the medial/lateral malleoli, second and fifth metatarsal heads, calcaneous at the level of the marker placed at the second metatarsal head, tibial tuberosities, medial/lateral tibial plateaus, medial/lateral condyles, greater trochanter, anterior superior iliac spine, superior portion of the iliac spine, posterior superior iliac spine, halfway between the superior portion of the iliac crest and the posterior superior iliac spine, and the manubrium. Additional markers were then clustered around the lower body segments. The shank 19
cluster markers were placed 8 cm below the tibial tuberosity, 8 cm below the lateral tibial plateau and 8 cm above the lateral malleolus. The rest of the shank markers were clustered in between these markers. The thigh cluster markers were placed 8 cm below the greater trochanter, 8 cm below the anterior superior iliac spine and 8 cm above the lateral condyle. The rest of the thigh markers were clustered in between these markers (Figure 2.3). Markers were also placed on the ends of the barbell and PVC pipe. Once the markers were placed, leg length was determined by measuring the distance between the anterior superior iliac spine marker and the medial malleolus marker for each leg with a tape measure. A still picture was then taken documenting an anterior and posterior view of the marker placement using a digital camera. Kinematic and kinetic data was recorded using an eight camera Vicon MX-F40 system (Oxford Metrics, Oxford, UK), two Bertec 4060-10 force plates (Bertec Corporation, Columbus, OH), and Vicon Nexus software (Oxford Metrics, Oxford, UK). The cameras were calibrated prior to each trial to minimize error from the cameras. Cameras were not calibrated again if two trials were scheduled one after the other. The calibration allowed the software to determine where each camera was in the lab in relation to the others as well as the force plates.
20
Figure 2.3: Marker placement.
21
The mass of the subject was first measured by having the subject place both feet on one of the force plates. Next, two calibration trials were recorded using the motion capture system. The first trial included all markers. This trial was used to define both the tracking and anatomic coordinate systems. The thigh, shank, and foot segments had a set of markers that was used to track each segment respectively which defines the coordinate system. Other markers attached to anatomical landmarks defined the anatomical coordinate system. Following this trial, markers on the medial femoral condyles of the knee, medial malleoli of the ankle, and tibial plateau were removed before the second trial was recorded (Figure 2.4). The medial markers were removed as the relationship between the anatomical and tracking coordinate systems were established in the first trial. In addition, removal of these markers allows the subject to move freely without the concern of knocking off markers. The tibial plateau markers were removed due to their close proximity to the femoral condyle markers.
22
Figure 2.4: Markers removed after 1st calibration trial.
23
A second calibration trial was captured after the removal of the medial markers. The Nexus software utilized this trial to auto-label future dynamic trials. Markers would often become very close together or become hidden for many of the squat trials and therefore this auto-label feature often needed user intervention. In addition, when markers could not be tracked for the entire trial, Nexus would calculate an estimated trajectory based on the motion before or after the gap or the motion of markers surrounding the marker in question. All gaps were filled manually by the same user to ensure the most accurate trajectory was used. The anterior superior iliac spine markers disappeared in nearly every trial due to the enveloping of the marker between the thigh and torso. The anterior superior iliac spine marker locations were calculated in relation to the posterior superior iliac spine and iliac crest markers. The first dynamic trial was conducted to find the subject’s hip joint centers. The subject performed motions at the hip which required lifting a straight leg in 5 positions around a half circle before returning it to the original position with an arcing motion (Figure 2.5). The leg motions consisted of raising the straight leg to the front, 45° angle to the front, side, 45° to the back, and straight back. The subject finished the straight back motion by making an arc back to the starting position. The hip joint center could then be calculated utilizing the methods described by Camomilla et al. [61]. The trial was performed with the subject standing on a small step with one leg and letting the other leg hang free. The subject was allowed to use their ipsilateral arm for balance while the other hand held onto a PVC pipe that was long enough to contact the ground.
24
Figure 2.5: Hip joint center posterior view (left) and superior view (right). Subjects were then instructed to perform a warm-up that they would typically engage in before their regular training. The 13 dynamic squat trials were randomly selected before the testing session using an Excel spreadsheet (see Appendix H). In addition to the motion capture, digital video of the sagittal plane was recorded for each trial using a Sony DCR-TRV18 digital video camera (Sony Corporation, New York, NY). Custom scripts in Matlab (The Mathworks, Natick, MA) and Vicon Bodybuilder (Oxford Metrics, Oxford, UK) were used to calculate knee kinematics and kinetics. This data utilized the femoral and tibial coordinate systems which were based on the PCT marker set [59]. The knee flexion axis was determined using the two markers placed on medial/lateral femoral condyles forming the transepicondylar line [62].
25
Three-dimensional marker data was filtered using a built-in Woltring filter [63]. Data was then analyzed in Microsoft Excel. Peak moments were extracted for each trial without regard to side. Knee flexion angles for peak knee moments and maximum knee angles were noted. Patellofemoral joint kinetics were then calculated utilizing Microsoft Excel using methods that are described in Section 2.6.
One Repetition Max Relationships Regression analysis was utilized to find the relationship among one repetition max weight and depth. Linear regression was performed using the above parallel 1RM weight to predict 1RM weight at the parallel and below parallel depths where correlations were significant (p < 0.05). Height and weight were additional variables considered to help better explain this relationship.
Patellofemoral Joint Kinetics Patellofemoral joint reaction force was calculated using a biomechanical model requiring the tibiofemoral moment (Mtf) and the tibiofemoral joint angle as input variables. An effective lever arm (Leff) for the quadriceps was calculated using a nonlinear equation (Leff = -0.000064x2+0.014x+0.37); where x = tibiofemoral joint angle) fit to the data (R2 = .94) of Gill and O’Connor [64]. Quadriceps force (Fq) was then calculated by dividing the net tibiofemoral extensor moment by the effective moment arm (Eq. (1)) Fq = Mtf / Leff 26
(Eq. 2.1)
Patellofemoral joint reaction force (JRFpf) was calculated as the product of the quadriceps force and a constant k (Eq. 2). The constant k was determined for each tibiofemoral joint position by using a non-linear equation (k = -0.000064x^2 + 0.014x + 0.37) fit to the data (R2 = 1.00) of Gill and O’Connor [64]. The constant k represents the relationship between patellofemoral joint reaction force and the force of the quadriceps (Fq) shown as JRFpf/ Fq. JRFpf = k · Fq
27
(Eq. 2.2)
CHAPTER 3
RESULTS
Population Sixteen subjects participated in this study. Subjects ranged from 18 to 33 years of age (22.69 ± 4.50). Weight ranged from 72.60 kg to 107.40 kg (85.36 ± 8.65) and height ranged from 171.45 cm to 187.33 cm (177.60 ± 3.82). Subject characteristics are presented in table 3.1. Average peak knee flexion angles were 98.21 ±7.99° for the 90° above parallel squat, 123.61 ±8.39° for the 110° parallel squat, and 140.51 ±8.45° for the 135° below parallel squat.
Age (yrs) Weight (kg) Height (cm)
Average
St. Dev.
Minimum
Maximum
22.69 85.36 177.60
4.50 8.65 3.82
18 72.60 171.45
33 107.40 187.33
Table 3.1 Subject Characteristics
28
Squat One Repetition Max and Depth There were significant differences found in squat one repetition max between the three squat levels (p < .05, Figure 3.1). Maximum squat 1RM was found at the 90° above parallel depth (150.24 kg) whereas the minimum squat 1RM was at the 135° below parallel depth (125.28 kg). The 110° parallel depth 1RM was only slightly higher than that of the below parallel depth (129.97 kg, p = .036).
180
*
160
*#
Squat 1RM (kg)
140 120 100 80 60 40 20 0 90° ‐ Above Parallel
110° ‐ Parallel Squat
135° ‐ Below Parallel Squat
Squat Depth
Figure 3.1: One repetition max values. * Significant difference from the above parallel squat (p < 0.001) # Significant difference from the parallel squat (p = 0.036) Error bars represent ±1 SD.
29
Regression analysis was performed to describe the relationship between a 90° above parallel 1RM with both a 110° parallel (Figure 3.2) 1RM and 135° below parallel 1RM (Figure 3.3). Both relationships were significantly correlated at the p < .001 level. Two regression equations were formed to describe the relationships (equations 3.1 and 3.2 where x = 90° above parallel 1RM in kg).
110° Parallel 1RM = 0.857(x) + 0.990 R2 = 0.764 (equation 3.1) 135° Below Parallel 1RM = 0.707(x) + 18.920 R2 = 0.641 (equation 3.2)
90° ‐ Above Parallel 1RM
200 180 160 140 120 100 80 80
100
120
140
160
180
200
110° ‐ Parallel 1RM
Figure 3.2: Relationship between one repetition max at a 90° above parallel squat and a 110° parallel squat. (p < 0.001; R2 = 0.764)
30
90° ‐ Above Parallel 1RM
200 180 160 140 120 100 80 80
100
120
140
160
180
200
135° ‐ Below Parallel 1RM
Figure 3.3: Relationship between one repetition max at a 90° above parallel squat and a 135° below parallel squat. (p < 0.001; R2 = 0.641)
Regression analysis was then performed with the variables representing height and weight. Height and weight were not significantly correlated for either the 110° parallel or the 135° below parallel 1RM and were therefore not included in the regression equation.
Peak External Knee Flexion Moments Peak external knee flexion moments were significantly different at all depths utilizing unloaded, 50% of the 135° 1RM and 85% of the 135° 1RM constant loads (Figure 3.4). Peak external knee flexion moments increased from 103.75 ±19.16 Nm at the 90° above parallel squat to 118.02 ± 24.87 Nm at the parallel squat and 129.03 ±28.86 Nm at the below parallel squat during unloaded trials. Peak external knee flexion 31
moments were also significantly different with increasing depth using constant loads of 50% of the 135° 1RM and 85% of the 135° 1RM. While squatting with the constant 50% load, peak external knee flexion moments increased from 152.53 ±29.50 Nm at the 90° above parallel squat to 177.82 ±43.62 Nm at the 110° parallel squat and 213.66 ±55.00 Nm at the 135° below parallel squat. With the constant 85% of the 135° 1RM, peak external knee flexion moments increased from 178.51 ±23.11 Nm at the 90° above parallel squat to 195.67 ±31.84 Nm at the 110° parallel squat and 246.29 ±58.45 Nm at the 135° below parallel squat.
32
350
Knee Flexion Moment (Nm)
300 c 250 200 a
150
a, b
100 50 0 90° ‐ Above Parallel Unloaded
110° ‐ Parallel
135° ‐ Below Parallel
Constant 50% 135° 1RM
Constant 85% 135° 1RM
Figure 3.4: Peak external knee flexion moments with constant loads. a Significant difference from the unloaded 90° above parallel squat (p < 0.004) b Significant difference from the unloaded 110° parallel squat (p = 0.017) c Significant difference from the constant 85% 135° 1RM 90° above parallel squat (p = 0.006) All other values across depths are significantly different at p < 0.001. Error bars represent ±1 SD.
33
During trials in which subjects performed a squat with a percentage of their 1RM at each respective depth, peak external knee flexion moments were significantly different at all trials (Figure 3.5). Peak external knee flexion moments increased from 152.53 ±29.50 Nm at the 90° above parallel squat to 177.82 ±43.62 Nm at the 110° parallel squat and 213.66 ±55.00 Nm at the 135° below parallel squat while squatting 50% 1RM. An increase in peak external knee flexion moments was also seen when squatting with 85% 1RM. Peak external knee flexion moments increased from 178.51 ±23.11 Nm at the 90° above parallel squat to 195.67 ±31.84 Nm at the 110° parallel squat and 246.29 ±58.45 Nm at the 135° below parallel squat. Across the different squat depths, increasing loads showed an increase in peak external knee flexion moments (Figure 3.5). At the 90° above parallel squat, peak external knee flexion moments increased from 103.75 ±19.16 Nm in the unloaded trial to 152.53 ±29.50 Nm at the 50% 1RM trial and 178.51 ±23.11 Nm at the 85% 1RM trial. Similar increases were seen at the 110° parallel and 135° below parallel depths. While squatting to 110° parallel depth, peak external knee flexion moments increased from 118.02 ±24.87 Nm during unloaded trials to 177.82 ±43.62 Nm at the 50% 1RM trial and 195.67 ±31.84 Nm at the 85% 1RM trial. Squatting to 135° below parallel depth showed increases from 129.03 ±28.86 Nm while squatting unloaded to 213.66 ±55.00 Nm with 50% 1RM loads and 246.29 ±58.45 Nm at 85% 1RM loads.
34
350
Knee Extensor Moment (Nm)
300 250
c, *
200 a, b
a
150 100 50 0 90° ‐ Above Parallel Unloaded
110° ‐ Parallel 50% 1RM
135° ‐ Below Parallel 85% 1RM
Figure 3.5: Peak external knee flexion moments with %1RM loads. a Significant difference from the unloaded 90° above parallel squat (p < 0.004) b Significant difference from the unloaded 110° parallel squat (p = 0.017) c Significant difference from the 85% 1RM 90° above parallel squat (p = 0.018) * Significant difference from the 50% 1RM 110° parallel squat (p = 0.020) All other values across depths and loads are significantly different at p ≤ 0.001. Error bars represent ±1 SD.
35
Patellofemoral Joint Reaction Force At the unloaded depth, PFJRF was significantly different from the 90° above parallel squat to each of the lower squat depths (Figure 3.6). The 110° parallel squat and 135° below parallel squat were not significantly different (p = 0.097). PFJRF increased from 4698.54 ±949.27 N at the 90° above parallel squat to 5399.90 ± 1119.09 N at the 110° parallel squat and 5739.01 ±1277.35 N at the 135° below parallel squat. PFJRF was also significantly different with increasing depth using constant loads of 50% of the 135° 1RM and 85% of the 135° 1RM. While squatting with the constant 50% load, PFJRF increased from 6390.44 ±1315.23 N at the 90° above parallel squat to 8160.34 ±1962.89 N at the 110° parallel squat and 9319.42 ±2412.17 N at the 135° below parallel squat. With the constant 85% of the 135° 1RM, PFJRF increased from 7256.07 ±1397.30 N at the 90° above parallel squat to 9243.22 ±2347.48 N at the 110° parallel squat and 10773.86 ±2565.94 N at the 135° below parallel squat.
36
Patellfeomral Joint Reaction Force (N)
14000 12000 10000 8000
X
6000 4000 2000 0 90° ‐ Above Parallel Unloaded
110° ‐ Parallel
135° ‐ Below Parallel
Constant 50% 135° 1RM
Constant 85% 135° 1RM
Figure 3.6: Patellofemoral joint reaction force with constant loads. X No significant difference from the unloaded 110° parallel squat (p = 0.097) All other values across depths are significantly different at p ≤ 0.001. Error bars represent ±1 SD.
37
Similar findings were found for constant loads when normalized for body weight (Figure 3.7). During the unloaded trials, PFJRF increased from 5.60 ±0.82 (* BW) for the 90° above parallel squat to 6.43 ±0.93 (* BW) for the 110° parallel squat and 6.83 ±1.09 (* BW) for the 135° below parallel squat. The 110° parallel squat and the 135° below parallel squat were not significantly different (p=0.90). Significant differences were found across all depths for constant loads of 50% of the 135° 1RM and 85% of the 135° 1RM. While performing the squat with the constant load of 50% of the 135° 1RM, PFJRF increased from 7.61 ±0.99 (* BW) at the 90° above parallel squat to 9.69 ±1.56 (* BW) at the 110° parallel squat and 11.02 ± (* BW) at the 135° below parallel squat. Increases were also seen with the constant load of 85% of the 135° 1RM with PFJRF increasing from 8.64 ±1.19 (* BW) at the 90° above parallel squat to 10.99 ±1.99 (* BW) at the 110° parallel squat and 12.79 ±2.14 at the 135° below parallel squat.
38
16
Patellofemoral Joint Reaction Force (* BW)
14 12 10 X 8 6 4 2 0 90° ‐ Above Parallel Unloaded
110° ‐ Parallel
Constant 50% 135° 1RM
135° ‐ Below Parallel Constant 85% 135° 1RM
Figure 3.7: Patellofemoral joint reaction force normalized by body weight with constant loads. X No significant difference from the unloaded 110° parallel squat (p = 0.090) All other values across depths are significantly different at p ≤ 0.002. Error bars represent ±1 SD.
39
During trials in which subjects performed a squat with a percentage of their 1RM at each respective depth, PFJRF was significantly different at all trials (Figure 3.8). PFJRF increased from 6698.26 ±1595.04 N at the 90° above parallel squat to 8178.72 ±1980.67 N at the 110° parallel squat and 9319.42 ±2412.17 at the 135° below parallel squat while squatting 50% 1RM. An increase in PFJRF was also seen when squatting with 85% 1RM. PFJRF increased from 7514.21 ±1199.93 N at the 90° above parallel squat to 8908.01 ±1602.38 N at the 110° parallel squat and 10773.86 ±2565.94 at the 135° below parallel squat. Across the different squat depths, increasing loads showed an increase in PFJRF (Figure 3.8). At the 90° above parallel squat, PFJRF increased from 4698.54 ±949.27 N in the unloaded trial to 6698.26 ±1595.04 N at the 50% 1RM trial and 7514.21 ±1199.93 N at the 85% 1RM trial. Similar increases were seen at the parallel and below parallel depths. While squatting to 110° parallel depth, external PFJRF increased from 5399.90 ±1119.09 N during unloaded trials to 8178.72 ±1980.67 N at the 50% 1RM trial and 8908.01 ±1602.38 at the 85% 1RM trial. Squatting to 135° below parallel depth showed increases from 5739.01 ±1277.35 N while squatting unloaded to 9319.42 ±2412.17 N with 50% 1RM loads and 10773.86 ±2565.94 N at 85% 1RM loads.
40
16000
Patellfeomral Joint Reaction Force (N)
14000 12000
*
10000 8000
X
6000 4000 2000 0 90° ‐ Above Parallel
110° ‐ Parallel
Unloaded
50% 1RM
135° ‐ Below Parallel 85% 1RM
Figure 3.8: Patellofemoral joint reaction force with %1RM loads. X No significant difference from the unloaded 110° parallel squat (p = 0.097) * Significant difference from the 50% 1RM 110° parallel squat (p = 0.030) All other values across depths and loads are significantly different at p ≤ 0.001. Error bars represent ±1 SD.
41
When normalized for body weight, PFJRF increased with increasing depth at each depth’s respective %1RM (Figure 3.9). At the 50% 1RM loads, PFJRF increased from 7.96 ±1.45 (* BW) at the 90° above parallel squat to 9.69 ±1.53 (*BW) at the 110° parallel squat and 11.02 ±1.82 at the 135° below parallel squat. Additionally, PFJRF increased from 8.99 ±1.19 (* BW) at the 90° above parallel squat to 10.65 ±1.58 (* BW) at the 110° parallel squat and 12.79 ±2.14 (* BW) at the 135° below parallel squat. In addition, similar patterns were found with differing squat loads across depths when normalized for body weight (Figure 3.9). During the 90° above parallel squat, PFJRF increased from 5.60 ±0.82 (* BW) during the unloaded trial to 7.96 ±1.45 (* BW) with a 50% 1RM load and 8.99 ±1.19 (* BW) with an 85% 1RM load. At the 110° parallel depth, PFJRF increased from 6.43 ±0.93 (* BW) during the unloaded trial to 9.69 ±1.53 (* BW) with a 50% 1RM load and 10.65 ±1.58 (* BW) with an 85% 1RM load. While performing the squat exercise at the 135° below parallel depth, increases in PFJRF were seen from 6.83 ±1.09 (* BW) with the unloaded trial to 11.02 ±1.82 (* BW) with a 50% 1RM load and 12.79 ±2.14 (* BW) with an 85% 1RM load.
42
16 14 Patellofemoral Joint Reaction Force (* BW)
* 12 10 8 6 4 2 0 90° ‐ Above Parallel Unloaded
110° ‐ Parallel 50% 1RM
135° ‐ Below Parallel
85% 1RM
Figure 3.9: Patellofemoral joint reaction force normalized by body weight with %1RM loads. X No significant difference from the unloaded 110° parallel squat (p = 0.090) * Significant difference from the 50% 1RM 110° parallel squat (p = 0.021) All other values across depths and loads are significantly different at p ≤ 0.002. Error bars represent ±1 SD.
43
CHAPTER 4
DISCUSSION
Main Findings This study demonstrated that the decreased loads typically seen with increasing depth in the back squat exercise were not enough to offset the increase in peak external knee flexion moments and patellofemoral joint reaction force seen with increasing knee flexion. These findings are somewhat contrary to previous squat research conducted by Wallace et al. who looked at PFJRF at 70°, 90°, and 110° of knee flexion finding no difference in PFJRF with a constant load [24]. Potential reasons for this conflict may be that Wallace utilized only females and had a small sample size of five subjects. The primary reason for the increase seen in PFJRF with increasing knee flexion is that the peak external knee flexion moments, and therefore quadriceps force, increased with increasing knee flexion. Although both peak external knee flexion moments and PFJRF increased with increasing flexion, there was only an increase of 10% and 38% from the 90° above parallel squat to the 110° parallel and 135° below parallel squat respectively for peak external knee flexion moments and 19% and 43% for PFJRF in the 85% 1RM trials. This is in contrast to some anecdotal beliefs that peak external knee 44
flexion moments and PFJRF increase exponentially with increasing knee flexion. Research for comparison purposes is lacking but one study comparing knee forces between patients with total knee replacements versus those with normal knees showed that both quadriceps force and patellofemoral force decrease fairly drastically following 120° of flexion to maximal flexion [65]. The authors reason that the femorotibial contact point moves posteriorly with increased flexion thereby increasing the moment arm. The moment arm is also simultaneously decreasing with increasing flexion due to the decrease in the angle of the quadriceps with the femur. After approximately 90° though, the quadriceps tendon wraps on the femur and the quadriceps angle with respect to the femur does not change therefore allowing the moment arm of the quadriceps increase. In response to this increase in the moment arm, the quadriceps force, and therefore PFJRF, decreases with maximal flexion [65-67]. Research looking at a deep knee bend with heels not on the ground also found a decrease in PFJRF at max knee flexion values [25]. In addition, many healthcare professionals utilize the unloaded back squat to help strengthen the quadriceps muscle and promote recovery from injury but will often not prescribe squats below 90° of knee flexion. This study showed a difference from the 90° above parallel squat to the deeper squats but increases were only 15% at the unloaded 110° parallel squat and 22% at the unloaded 135° below parallel squat. There was no difference seen at the parallel and below parallel squat levels with unloaded trials. Not surprisingly, increases were also seen in peak external knee flexion moments and PFJRF when increasing but constant loads were used at increasing squat depths. 45
Previous research has shown increasing peak external knee flexion moments and PFJRF up to 90° of flexion during squatting activities with increasing loads [23]. The loads used were considered very light for training purposes at 35% of body weight. These individuals, although status was not listed, were most likely untrained or recreationally trained. This may be the reason for the contrast in results compared to the work done with female collegiate athletes by Salem and Powers previously discussed that showed no change with depths up to approximately 110° [24]. This study adds that using a constant load while squatting to full depth increases both peak external knee flexion moments and PFJRF. Increasing the constant load increases these variables further. Values found in this study only moderately reflect values found in literature. Two studies looking at bodyweight squats to maximal flexion found PFJRF ranging from 5455 N and 6377 N both of which were found at the near maximal knee flexion angle [25, 68]. Both studies utilized a two-dimensional model utilizing photographs for lower leg activity. This agrees fairly well with the PFJRF of 4698.54 N, 5399.90 N, and 5739.01 N for the 90° above parallel, 110° parallel, and 135° below parallel unloaded squats found in this study. Wretenberg et al. [17] utilized video recording and a computer program based on free-body dynamics to look at both experienced powerlifters and Olympic weightlifters to 120° of flexion and found PFJRF values of 3300 N and 4700 N respectively for each type of lifter. Although experienced, the mean loads of 100 kg for powerlifters and 66.28 kg for Olympic weightlifters are considered rather light for experienced lifters. Regardless of the loads used, PFJRF from Wretenberg’s study are much lower than even the unloaded values experienced for this study. Motion capture 46
utilizing a three-dimensional link model and inverse dynamics found that squatting to a depth of 95° with heavier loads of approximately 140 kg showed PFJRF of approximately 4500 N [3, 49]. This value is still quite lower than the value of 7514.21 N found for the 85% 1RM 90° above parallel squat in this study which utilized a mean load of 150.24 kg. The highest mean load used in previous literature for a below parallel squat depth was 250 kg. PFJRF was found to be 6750 N at the deepest knee flexion angle of approximately 130° utilizing a sagittal plane biomechanical model [69]. Although much heavier than the 85% 1RM trials from the current study, this value is near the PFJRF for the unloaded trials as well as the other unloaded trials previously mentioned [25, 68]. Variation in PFJRF may potentially be caused by the different biomechanical models used in measuring PFJRF as well as the large variance in subject experience and loads utilized.
Patellofemoral Joint Reaction Force Model Patellofemoral joint reaction force was calculated in this study by finding the quadriceps force which was calculated by dividing the tibiofemoral moment by an effective quadriceps lever arm (Eq. 2.1). The effective quadriceps lever arm was derived from data obtained from Gill and O’Connor [64] which utilized a biarticulating twodimensional model of the patellofemoral joint up to 140° and is defined as the perpendicular distance from the central axis of the patellar ligament to the tibiofemoral contact point multiplied by the ratio of patellar ligament force to quadriceps tendon force [24]. The quadriceps effective lever arm represents the mechanical advantage of the 47
quadriceps muscle group. In other words, the greater the quadriceps effective lever arm, the less quadriceps force is needed to create a given moment. Data from Gill and O’Connor show a constant decline in the quadriceps effective lever arm from 0° of knee flexion to approximately 100° of knee flexion. Following 100° of knee flexion, there was a small rise and then another steady decrease to 130° of knee flexion. From 130° to 140° of knee flexion, there was a somewhat sharp drop-off. When a non-linear equation was created for the effective quadriceps lever arm, knee flexion angles greater than 140° showed unusually low values for the effective quadriceps lever arm as a result of the sharp decline in values after 130° of knee flexion. Data collected by Fick [70] that looked at moments of the rectus femoris up to knee flexion values of 160° showed that the rectus femoris moment arm appears to stay rather constant after approximately 85° of knee flexion. Data by Buford also reflect a similar pattern for the rectus femoris up to 130° of knee flexion [71]. Both Fick and Buford utilized a tendon displacement method. Other studies looking at squat depths up to parallel [23, 24] with similar methods to the current study utilized data from a mathematical model developed by van Eijden [72]. In Figure 4.1, the moment arm of the rectus femoris (Fick and Buford) and the effective quadriceps lever arm (Gill and O’Connor and van Eijden) are overlaid for comparison purposes. Considering this information, data was extrapolated following that of Gill and O’Connor after 140° to represent a fairly constant effective quadriceps lever arm. In contrast, Sharma et al. [65] reported decreasing quadriceps force and PFJRF with increasing flexion past 120° relating this to an increase in the effective quadriceps lever arm at deeper flexion. Unfortunately, maximum values for knee flexion ranged from 48
126° to 160° therefore making any conclusion about data at deeper flexion angles difficult. At this point, there appears to be no clear understanding of the quadriceps effective lever arm at deeper knee flexion.
Gill and O'Connor (1996)
van Eijden (1987)
0
60
Buford (1997)
Fick (1879)
60
Moment Arm (mm)
50 40 30 20 10 0 20
40
80
100
120
140
160
Knee Flexion Angle
Figure 4.1: Moment arm of the rectus femoris (Buford and Fick) and the effective quadriceps lever arm (Gill and O’Connor and van Eijden) for comparison purposes.
Data from Gill and O’Connor [64] was also used to formulate a non-linear equation representing the JRFpf / Fq ratio. This data is reportedly higher than other published data for knee flexion values greater than 60° [65, 73, 74]. The authors report that these higher values are a result of the assumptions made with their model that 1) the 49
quadriceps tendon is parallel to the long axis of the femur until wrap occurs and 2) the contact point between the patella and the femur lies on the straight line joining the centers of curvature of the patella and the trochlea or the femoral condyle. This may therefore overestimate the PFJRF for the data presented from this study. In contrast, the current study does not take into consideration co-contraction of the hamstrings. Co-contraction of the hamstrings has been shown to increase patellofemoral contact pressures [75]. The values for peak external knee flexion moments and PJFRF were probably underestimated in this respect.
Limitations This study provides insight into how both load and depth affect peak knee flexion moments as well as PJFRF. Interpretation of these results should be done with an appreciation for the limitations of this study. Squat testing was conducted utilizing an apparatus that measured depth and subsequently forced the subject to hold that position for one second before rising. This was done to limit any bouncing that may have occurred especially at deeper squats as well as more accurately measure depths. Many subjects struggled with finding the correct depth even with practice. Subjects would descend into a squat and generally stop at the depth they felt was correct. This depth was not always deep enough. Upon noticing the depth was not achieved, the subjects would then descend again until the light would go off signaling that the proper depth was achieved. This stop and start of the squat could potentially alter the peak external knee flexion moments and therefore 50
PFJRF. In addition, many subjects reported that the 110° parallel squat was challenging during the 1RM testing due to the one second hold that was required. The hold was not as challenging in the 135° below parallel squat position due to the thigh-calf contact which made the one second hold less challenging. Future studies may want to improve the technique for measuring depth by adding a visual or audible cue showing how close the subject is to the desired depth. As previously discussed, co-contraction of the hamstring muscle group was not modeled in this study which would increase the values reported. On the other hand, evidence of increased thigh-calf contact may decrease the values reported at higher flexion values. When squatting to deeper depths, at approximately 130° of knee flexion, the thigh comes into contact with the calf. This thigh-calf contact produces a moment in the same direction as that of the quadriceps muscle group thereby decreasing forces at the knee. Zelle et al. [76] examined tibiofemoral compressive force, shear force, and patellar tendon force while squatting to full depth. All forces decreased as thigh-calf contact increased. There were strong correlations found with body mass index (R2 = 0.46) and sum of thigh and calf circumference (R2 = 0.79) tibiofemoral compressive force reduction. Compressive forces decreased from 4.37 to 3.07 (* body weight) at maximal flexion (155°). Additionally, Caruntu et al. [77] reported decreases in quadriceps force from 3500 N to 2800 N when thigh-calf contact was taken into consideration. Although values were not given, it was also reported that tibiofemoral and patellofemoral contact forces were lower than previous predictions. Thigh-calf contact should be considered in
51
future models for predicting forces about the knee. Knee forces at deeper depths are therefore most likely overestimated in the current research study. Many believe that increased stress, versus strictly PFJRF, is the mechanical stimulus that causes deterioration of the articular cartilage and subsequent subchondral bone degeneration [22]. Patellofemoral joint stress is defined a PFJRF divided by contact area. It is well-known that patellofemoral contact area increases steadily with knee flexion up to 90° [78-80] yet little is known about patellofemoral contact area beyond 90°. Nakagawa reports that mean contact area remains fairly constant from 3.43 ± 0.70 cm2 at 90° of knee flexion to 3.62 ± 0.72 cm2 at maximal flexion of approximately 140° [81]. Although patellofemoral contact remain fairly constant, other compensatory mechanisms such as the force absorbed by the quadriceps tendon as it contacts the trochlea along with hydrostatic pressure resulting from contact with the fat pad may help distribute forces at greater degrees of knee flexion. The values reported by Nakagawa utilized samples from a Japanese population which were shorter in stature (172 ± 5 cm) and weight (67.7 ± 8.7 kg) than many non-Japanese populations. Subjects of greater stature may have increased patella size and show larger increases in contact area seen with increasing knee flexion. Future studies should look more closely at contact area at deeper knee flexion as well as other compensatory mechanisms for distributing force across the knee joint. Caution should be taken in generalizing the results of this study as only recreationally trained males were studied. Females have been shown to have different patellofemoral joint biomechanics than males and therefore the results reported here 52
cannot be generalized to females [56]. In addition, the males recruited were recreationally trained and had at least one year’s experience resistance training. Although many reported several years of training, it was clear there was a wide range of abilities in squatting independent of experience. In fact, four subjects did not increase the 1RM from the 135° below parallel squat to the 110° parallel squat and two subjects decreased their 1RM from the 135° below parallel squat to the 110° parallel squat. Some subjects reported that the 110° parallel squat was somewhat more challenging due to the one second pause that was required at the bottom position. Compared to the 135° below parallel squat in which the subject could rest the thighs against the calf area, the hold at the 110° parallel squat position had to be maintained by muscular contraction. This phenomenon is most likely a result from a lack of experience in squatting large loads at deeper depths. In general, most subjects increased 1RM weight as squat depth decreased. Although some subjects did not increase 1RM weight with decreasing depth, the data achieved from this particular sample may be more representative of individuals who recreationally resistance train. Individuals that have more experience may show greater differences between 1RM weights at varying depths potentially affecting peak external knee flexion moments and PFJRF. There were several obstacles in obtaining motion capture data during this study. A squat rack was utilized to not only support the barbell, but to provide supports that would catch the weight in the event the subject could not complete a repetition. This was done to provide a safe atmosphere for the subjects to squat. The rack though did prove to be an extra barrier between the subject and the motion cameras. We initially had 53
subjects squat by walking the bar backwards as is typically done when squatting. Considering that most of the subjects’ markers are placed on the anterior of the body, the rack blocked the view of many markers from the camera. This was corrected by having the subject face in the opposite direction away from the rack. Subjects would then have to walk the bar forward versus backwards. Subjects appeared to have no trouble with the adjustment. Careful placement of the surrounding equipment allowed adequate collection of marker data. There were though several events in which markers could not be captured for significant periods of time. In these instances, the missing markers would not be used. The anterior superior iliac spine markers were consistently gone for most trials due to the envelopment of the markers between the upper and lower body while squatting. These markers were recreated using a custom script that calculated their location based on the location of the posterior superior iliac spine and iliac crest markers. The markers of the upper thigh including the greater trochanter were removed before analysis due to its disappearance with many subjects. Future studies need to balance safety with accuracy. We believe that the inclusion of a squat rack for safety reasons superseded the need for a clearer view of the subject. Marker movement that occurred with deeper squats may have affected values reported in this study. As depth increased, the cluster of markers on the thigh became closely packed together causing the femur to track forward on the Nexus software. Although markers on the lateral condyles of the knee simultaneously moved backwards, translation of the femur anteriorly over the tibia may cause an overestimation of values
54
presented in this study. Optimal placement of markers on the thigh and pelvis should be considered in future studies.
Practical Applications This study concluded that with increasing depth of the back squat, peak external knee flexion moments and PFJRF increased. Although it might be easy to come to a conclusion that deeper squats should therefore be avoided, there are many other factors that should be taken into consideration. There is currently no knowledge as to what magnitude or threshold level for repetitive force is considered injurious for the knee. The current study introduces how depth and load affect patellofemoral joint kinetics but not its outcome on knee pathology. Much debate over squat depth comes from professionals that are coming from two different areas of expertise. Health professionals such as physical therapists, athletic trainers and medical doctors are looking to keep patients either healthy or get them back to comparable health. Sport professionals such as strength and conditioning coaches, personal trainers, and sport specific coaches look for methods that optimally increase performance. With these two different viewpoints, there is often an opposite idea as to what an individual should do concerning training with the squat exercise. Health professionals generally will instruct individuals to not squat below a certain depth to limit forces about the knee whereas sport professionals will generally state that deeper depths are necessary for proper performance development. Such generalizations cannot often be made as there is a large range of individual variation in training environment, 55
experience, previous injuries, etc. Professionals need to therefore be able to incorporate current knowledge on safe practices and training methods to suit each individual’s interest. Those without any previous or current knee pathologies that have access to proper methods of instruction for performing the squat exercise may find no problems with performing a deep squat whereas someone with previous complaints of patellofemoral pain may not be able to tolerate deeper depths. Although peak external knee flexion moments and PFJRF increased with increasing knee flexion, increases were not greatly different between depths. The largest increases seen in this study were seen with the constant 135˚ 1RM from the 90° above parallel squat to the 135° below parallel squat in which there was a 48% increase in both peak external knee flexion moments and PFJRF. Some increases were much smaller such as a 22% increase in PFJRF from an unloaded 90° above parallel squat to an unloaded 135° below parallel squat. The increase is even smaller from the 110° parallel squat to the 135° below parallel squat in which there was only a 6% non-significant increase. The small increases seen with unloaded squats may suggest that if range of motion is desired, unloaded squat training at lower depths may not compromise the patellofemoral joint. The effect of load on any particular depth showed a trend towards a leveling off of PFJRF with increased loads. There was a steeper rise in PFJRF when load increased from an unloaded squat to a 50% 1RM squat. The increase seen in PFJRF when the load increased from 50% 1RM to 85% 1RM was much less steep. Although the load increase from 50% 1RM to 85% 1RM is less than that from unloaded to 50%, the trend is still 56
seen when normalized for the increase in load. This data suggests that after adding a load to a squat, there is less of an increase in PFJRF when further loads are added. Considering that it is currently unknown as to what magnitude of force or repeated joint stress leads to increased risk for patellofemoral pain, proper progression and periodization should be utilized to help decrease the risk of patellofemoral pain. Increased PFJRF with increasing depth also signifies increased force of the quadriceps. The data in this study suggests that lighter loads may be used with deeper squats to elicit quadriceps force compared to higher loads in a shallower squat. Lighter loads in a deeper squat are also potentially safer than greater loads in a shallower squat. It was shown in this study that 1RM decreased with increasing depth. If loaded squats are prescribed to shallow depths and the participant achieves a deeper depth while fatigued, the participant may fail in that squat due to the inability to handle greater loads with increasing depth therefore causing increased risk for injury. In a squat where the hamstrings contact the calves, the participant is well aware of the depth they need to achieve for each repetition allowing for less risk for failing during the squat exercise. In addition to the ideas presented in this section, the previously mentioned limitations need to be taken into consideration before making any conclusions. At this time, health professionals are encouraged to take the research presented with its limitations and apply it to individuals based on their individual backgrounds rather than making generalizations.
57
Conclusions The main findings of this study are that 1RM decreases with increasing depth but these decreases are not enough to offset the increases in peak knee flexion moments and PFJRF at loads consisting of unloaded, 50% 1RM and 85% 1RM typically seen with increasing flexion. Increases in peak external knee flexion moments and PFJRF are greater when increasing load from unloaded to 50% 1RM than from 50% 1RM to 85% 1RM. There is no difference in PFJRF in 110° parallel and 135° below parallel unloaded trials. To our knowledge this is the first study investigating peak external knee flexion moments and PFJRF utilizing a range of typical loads and depths found in rehabilitation and performance training settings. Health professionals should take the information presented here in addition to individual assessments to determine how to best incorporate the squat exercise into rehabilitation and training programs.
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LIST OF REFERENCES
1.
O'Shea, J., The parallel squat. National Strength & Conditioning Association Journal, 1985. 7(1): p. 4-6.
2.
Coaches Roundtable: The squat and its application to athletic performance. National Strength & Conditioning Association Journal, 1984. 6(3): p. 10-23.
3.
Escamilla, R.F., et al., Effects of technique variations on knee biomechanics during the squat and leg press. Medicine and Science in Sports and Exercise, 2001. 33(9): p. 1552-66.
4.
Neitzel, J.A. and G.J. Davies, The benefits and controversy of the parallel squat in strength training and rehabilitation. Strength & Conditioning Journal, 2000. 22(3): p. 30-37.
5.
Franklin, B., et al., ACSM's Guidelines for Exercise Testing and Prescription: Testing and Prescription. 2000: Lippincott Williams and Wilkins.
6.
Cook, G., Athletic body in balance. 2003: Human Kinetics.
7.
Mulholland, S.J. and U.P. Wyss, Activities of daily living in non-Western cultures: range of motion requirements for hip and knee joint implants. Int J Rehabil Res, 2001. 24(3): p. 191-8.
8.
Weiss, J.M., et al., What functional activities are important to patients with knee replacements? Clin Orthop Relat Res, 2002(404): p. 172-88.
9.
Escamilla, R.F., Knee biomechanics of the dynamic squat exercise. Medicine and Science in Sports and Exercise, 2001. 33(1): p. 127-41. 59
10.
Gullett, J.C., et al., A biomechanical comparison of back and front squats in healthy trained individuals. J Strength Cond Res, 2009. 23(1): p. 284-92.
11.
Lutz, G.E., et al., Comparison of tibiofemoral joint forces during open-kineticchain and closed-kinetic-chain exercises. J Bone Joint Surg Am, 1993. 75(5): p. 732-9.
12.
Palmitier, R.A., et al., Kinetic chain exercise in knee rehabilitation. Sports Med, 1991. 11(6): p. 402-13.
13.
McCaw, S.T. and D.R. Melrose, Stance width and bar load effects on leg muscle activity during the parallel squat. Med Sci Sports Exerc, 1999. 31(3): p. 428-36.
14.
Paoli, A., G. Marcolin, and N. Petrone, The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads. J Strength Cond Res, 2009. 23(1): p. 246-50.
15.
Boyden, G., J. Kingman, and R. Dyson, A comparison of quadriceps electromyographic activity with the position of the foot during the parallel squat. Journal of Strength & Conditioning Research, 2000. 14(4): p. 379-382.
16.
Signorile, J.F., et al., Effect of foot position on the electromyographical activity of the superficial quadriceps muscles during the parallel squat and knee extension. Journal of Strength & Conditioning Research, 1995. 9(3): p. 182-187.
17.
Wretenberg, P., Y. Feng, and U.P. Arborelius, High- and low-bar squatting techniques during weight-training. Med Sci Sports Exerc, 1996. 28(2): p. 218-24.
18.
Caterisano, A., et al., The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles. Journal of Strength and Conditioning Research / National Strength & Conditioning Association, 2002. 16(3): p. 428-32.
19.
Klein, K.K., The deep squat exercise as utilized in weight training for athletes and its effects on ligaments on the knee. J. Assoc. Phys. Ment. Rehabil., 1961. 15: p. 6-11.
60
20.
Steiner, M.E., et al., The effect of exercise on anterior-posterior knee laxity. Am J Sports Med, 1986. 14(1): p. 24-9.
21.
Chandler, T.J., G.D. Wilson, and M.H. Stone, The effect of the squat exercise on knee stability. Med Sci Sports Exerc, 1989. 21(3): p. 299-303.
22.
LaBella, C., Patellofemoral pain syndrome: evaluation and treatment. Primary Care, 2004. 31(4): p. 977-1003.
23.
Wallace, D.A., et al., Patellofemoral joint kinetics while squatting with and without an external load. The Journal of Orthopaedic and Sports Physical Therapy, 2002. 32(4): p. 141-8.
24.
Salem, G.J. and C.M. Powers, Patellofemoral joint kinetics during squatting in collegiate women athletes. Clinical Biomechanics, 2001. 16(5): p. 424-30.
25.
Dahlkvist, N.J., P. Mayo, and B.B. Seedhom, Forces during squatting and rising from a deep squat. Engineering in Medicine, 1982. 11(2): p. 69-76.
26.
Devereaux, M.D. and S.M. Lachmann, Patello-femoral arthralgia in athletes attending a Sports Injury Clinic. Br J Sports Med, 1984. 18(1): p. 18-21.
27.
Earl, J.E. and C.S. Vetter, Patellofemoral pain. Physical Medicine and Rehabilitation Clinics of North America, 2007. 18(3): p. 439-58, viii.
28.
Witvrouw, E., et al., Intrinsic risk factors for the development of anterior knee pain in an athletic population. A two-year prospective study. Am J Sports Med, 2000. 28(4): p. 480-9.
29.
DeHaven, K.E. and D.M. Lintner, Athletic injuries: comparison by age, sport, and gender. Am J Sports Med, 1986. 14(3): p. 218-24.
30.
Hungerford, D.S. and M. Barry, Biomechanics of the patellofemoral joint. Clin Orthop Relat Res, 1979(144): p. 9-15.
61
31.
Powers, C.M., R. Maffucci, and S. Hampton, Rearfoot posture in subjects with patellofemoral pain. J Orthop Sports Phys Ther, 1995. 22(4): p. 155-60.
32.
Woodall, W.R. and J. Welsh, A biomechanical basis for rehabilitation programs involving the patellofemoral joint. J Orthop Sports Phys Ther, 1990. 11(11): p. 535-42.
33.
Brindle, T.J., C. Mattacola, and J. McCrory, Electromyographic changes in the gluteus medius during stair ascent and descent in subjects with anterior knee pain. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA, 2003. 11(4): p. 244.
34.
Ireland, M.L., et al., Hip strength in females with and without patellofemoral pain. Journal of Orthopaedic & Sports Physical Therapy, 2003. 33(11): p. 671.
35.
Witonski, D., Anterior knee pain syndrome. International Orthopaedics, 1999. 23(6): p. 341.
36.
Boucher, J.P., et al., Quadriceps femoris muscle activity in patellofemoral pain syndrome. Am J Sports Med, 1992. 20(5): p. 527-32.
37.
Brindle, T.J., C. Mattacola, and J. McCrory, Electromyographic changes in the gluteus medius during stair ascent and descent in subjects with anterior knee pain. Knee Surg Sports Traumatol Arthrosc, 2003. 11(4): p. 244-51.
38.
Karst, G.M. and G.M. Willett, Onset timing of electromyographic activity in the vastus medialis oblique and vastus lateralis muscles in subjects with and without patellofemoral pain syndrome. Phys Ther, 1995. 75(9): p. 813-23.
39.
MacIntyre, D.L. and D.G. Robertson, Quadriceps muscle activity in women runners with and without patellofemoral pain syndrome. Arch Phys Med Rehabil, 1992. 73(1): p. 10-4.
40.
Mohr, K.J., et al., Electromyography of the quadriceps in patellofemoral pain with patellar subluxation. Clinical Orthopaedics & Related Research, 2003(415): p. 261. 62
41.
Moller, B.N., et al., Isometric contractions in the patellofemoral pain syndrome. An electromyographic study. Archives of orthopaedic and traumatic surgery. Archiv fur orthopadische und Unfall-Chirurgie, 1986. 105(1): p. 24.
42.
Powers, C.M., R. Landel, and J. Perry, Timing and intensity of vastus muscle activity during functional activities in subjects with and without patellofemoral pain. Phys Ther, 1996. 76(9): p. 946-55; discussion 956-67.
43.
Doucette, S.A. and D.D. Child, The effect of open and closed chain exercise and knee joint position on patellar tracking in lateral patellar compression syndrome. J Orthop Sports Phys Ther, 1996. 23(2): p. 104-10.
44.
Steinkamp, L.A., et al., Biomechanical considerations in patellofemoral joint rehabilitation. Am J Sports Med, 1993. 21(3): p. 438-44.
45.
Stiene, H.A., et al., A comparison of closed kinetic chain and isokinetic joint isolation exercise in patients with patellofemoral dysfunction. J Orthop Sports Phys Ther, 1996. 24(3): p. 136-41.
46.
Witvrouw, E., et al., Open versus closed kinetic chain exercises for patellofemoral pain. A prospective, randomized study. The American Journal of Sports Medicine, 2000. 28(5): p. 687-94.
47.
Witvrouw, E., et al., Open versus closed kinetic chain exercises in patellofemoral pain: a 5-year prospective randomized study. The American Journal of Sports Medicine, 2004. 32(5): p. 1122-30.
48.
Augustsson, J., et al., Weight training of the thigh muscles using closed vs. open kinetic chain exercises: a comparison of performance enhancement. J Orthop Sports Phys Ther, 1998. 27(1): p. 3-8.
49.
Escamilla, R.F., et al., Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Med Sci Sports Exerc, 1998. 30(4): p. 556-69.
50.
Jenkins, W.L., et al., A measurement of anterior tibial displacement in the closed and open kinetic chain. J Orthop Sports Phys Ther, 1997. 25(1): p. 49-56. 63
51.
Siegel, J., et al., Human muscle power output during upper-and lower-body exercises. The Journal of Strength and Conditioning Research, 2002. 16(2): p. 173-178.
52.
Kawamori, N. and G. Haff, The optimal training load for the development of muscular power. Journal of Strength & Conditioning Research, 2004. 18(3): p. 675-684.
53.
Berger, R., Optimum repetitions for the development of strength. Res Q, 1962. 33: p. 334-338.
54.
Campos, G., et al., Muscular adaptations in response to three different resistancetraining regimens: specificity of repetition maximum training zones. European journal of applied physiology, 2002. 88(1): p. 50-60.
55.
Faul, F., et al., G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods, 2007. 39(2): p. 175-91.
56.
Csintalan, R.P., et al., Gender differences in patellofemoral joint biomechanics. Clinical Orthopaedics and Related Research, 2002(402): p. 260-9.
57.
Baechle, T. and R. Earle, Essentials of strength training and conditioning. 2000: Human Kinetics Champaign.
58.
Matuszak, M.E., et al., Effect of rest interval length on repeated 1 repetition maximum back squats. Journal of Strength and Conditioning Research / National Strength & Conditioning Association, 2003. 17(4): p. 634-7.
59.
Andriacchi, T.P., et al., A point cluster method for in vivo motion analysis: applied to a study of knee kinematics. Journal of Biomechanical Engineering, 1998. 120(6): p. 743-9.
60.
Dyrby, C.O. and T.P. Andriacchi, Secondary motions of the knee during weight bearing and non-weight bearing activities. Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society, 2004. 22(4): p. 794800. 64
61.
Camomilla, V., et al., An optimized protocol for hip joint centre determination using the functional method. J Biomech, 2006. 39(6): p. 1096-106.
62.
Churchill, D., et al., The transepicondylar axis approximates the optimal flexion axis of the knee. Clinical Orthopaedics and Related Research, 1998: p. 111-118.
63.
Woltring, H.J., Smoothing and differentiation techniques applied to 3-D data, in Three-Dimensional Analysis of Human Movement, P. Allard, I.A.F. Stokes, and J.P. Blanchi, Editors. 1995, Human Kinetics: Champaign. p. 79-99.
64.
Gill, H.S. and J.J. O'Connor, Biarticulating two-dimensional computer model of the human patellofemoral joint. Clin Biomech (Bristol, Avon), 1996. 11(2): p. 8189.
65.
Sharma, A., et al., In vivo patellofemoral forces in high flexion total knee arthroplasty. J Biomech, 2008. 41(3): p. 642-8.
66.
Browne, C., et al., Patellofemoral forces after total knee arthroplasty: effect of extensor moment arm. Knee, 2005. 12(2): p. 81-88.
67.
Churchill, D., et al., The influence of femoral rollback on patellofemoral contact loads in total knee arthroplasty. J Arthroplasty, 2001. 16(7): p. 909-918.
68.
Reilly, D. and M. Martens, Experimental analysis of the quadriceps muscle force and patello-femoral joint reaction force for various activities. Acta Orthop Scand, 1972. 43(2): p. 126.
69.
Nisell, R. and J. Ekholm, Joint load during the parallel squat in powerlifting and force analysis of in vivo bilateral quadriceps tendon rupture. Scand J. Sports Sci, 1986. 8(2): p. 63-70.
70.
Fick, E., Über zweigelenkige Muskeln. Arch Anat Physiol (Anat Abt), 1879: p. 201-239.
71.
Buford, W.L., Jr., et al., Muscle balance at the knee--moment arms for the normal knee and the ACL-minus knee. IEEE Trans Rehabil Eng, 1997. 5(4): p. 367-79. 65
72.
van Eijden, T.M., et al., Forces acting on the patella during maximal voluntary contraction of the quadriceps femoris muscle at different knee flexion/extension angles. Acta Anat (Basel), 1987. 129(4): p. 310-4.
73.
van Eijden, T.M., et al., A mathematical model of the patellofemoral joint. J Biomech, 1986. 19(3): p. 219-29.
74.
Yamaguchi, G.T. and F.E. Zajac, A planar model of the knee joint to characterize the knee extensor mechanism. J Biomech, 1989. 22(1): p. 1-10.
75.
Lee, T.Q., G. Morris, and R.P. Csintalan, The influence of tibial and femoral rotation on patellofemoral contact area and pressure. J Orthop Sports Phys Ther, 2003. 33(11): p. 686-93.
76.
Zelle, J., et al., Thigh-calf contact: does it affect the loading of the knee in the high-flexion range? J Biomech, 2009. 42(5): p. 587-93.
77.
Caruntu, D., et al. Modeling the knee joint in deep flexion: Thigh and calf contact. in Summer Bioengineering Conference. 2003. Key Biscayne, Florida.
78.
Besier, T.F., et al., Patellofemoral joint contact area increases with knee flexion and weight-bearing. Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society, 2005. 23(2): p. 345-50.
79.
Huberti, H.H. and W.C. Hayes, Patellofemoral contact pressures. The influence of q-angle and tendofemoral contact. The Journal of Bone and Joint Surgery. American Volume, 1984. 66(5): p. 715-24.
80.
Salsich, G.B., et al., In vivo assessment of patellofemoral joint contact area in individuals who are pain free. Clinical Orthopaedics and Related Research, 2003(417): p. 277-84.
81.
Nakagawa, S., et al., Kinematics of the patella in deep flexion. Analysis with magnetic resonance imaging. J Bone Joint Surg Am, 2003. 85-A(7): p. 1238-42.
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APPENDIX A IRB APPROVAL LETTER
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APPENDIX B IRB APPLICATION
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APPENDIX C RECRUITMENT FLYER
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APPENDIX D CONSENT FORM
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APPENDIX E HIPAA FORM
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APPENDIX F ONE REPETITION MAX COLLECTION WORKSHEET
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APPENDIX G DATA COLLECTION WORKSHEET
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APPENDIX H SQUAT TRIAL WORKSHEET
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APPENDIX I RAW SUBJECT DATA
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Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Weight (kg) 81.96 76.45 93.50 86.10 107.40 90.01 88.70 90.32 80.30 82.82 72.60 91.19 85.32 87.40 73.80 77.88
Height (cm) 179.07 175.26 175.26 172.72 178.44 178.44 173.99 178.44 179.07 179.07 176.53 182.88 187.33 176.53 171.45 177.17
90° 1RM (kg) 111.36 143.18 170.45 143.18 156.82 152.27 170.45 147.73 136.36 170.45 134.09 179.55 152.27 170.45 152.27 115.91
Age 19 22 21 27 24 33 20 31 20 27 20 19 22 20 18 20
110° 1RM (kg) 106.82 129.55 152.27 138.64 147.73 115.91 136.36 134.09 111.36 156.82 106.82 156.82 125.00 143.18 125.00 93.18
Table I.1. Baseline demographics and one repetition max data.
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135° 1RM (kg) 102.27 115.91 143.18 138.64 147.73 106.82 125.00 125.00 106.82 147.73 102.27 143.18 125.00 143.18 129.55 102.27
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 101.72 107.55 112.11 106.13 108.64 110.56 98.6 101.98 106.87 100.78 108.31 90.34 109.2 99.41 108.57 110.03
Peak Tibiofemoral Angle - 90° 50% 85% 50% 135 1RM 1RM 1RM 95.94 91.48 100.11 86.81 91.05 94.86 94.24 81.70 95.44 89.30 93.11 97.55 108.2 101.84 112.07 103.96 98.85 104.74 95.55 88.31 95.92 106.33 99.95 107.28 108.24 105.21 102.92 93.94 92.3 92.42 97.14 97.39 104.22 81.30 79.54 83.88 101.67 96.61 93.24 89.90 86.36 88.73 103.63 97.28 110.71 101.17 100.15 106.1
85% 135° 1RM 90.35 90.89 90.49 97.22 102.84 101.79 91.39 101.51 102.18 86.93 93.44 84.96 97.69 88.59 101.07 106.32
Table I.2. Peak tibiofemoral angles for the 90° above parallel squat trials.
105
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 123.18 114.83 135.32 116.57 128.43 134.99 124.96 130.66 141.29 112.65 126.95 102.45 131.18 120.45 130.21 126.97
Peak Tibiofemoral Angle - 110° 50% 85% 50% 135 85% 135° 1RM 1RM 1RM 1RM 129.4 123.18 127.81 123.71 114.85 115.04 121.3 119.08 126.03 113.77 125.02 124.82 124.96 116.71 124.96 115.58 131.63 121.90 130.48 133.23 136.88 130.47 139.39 133.25 121.26 118.50 121.31 116.65 132.45 124.60 134.01 123.72 132.27 128.27 128.60 122.75 117.38 108.38 115.36 107.83 119.24 121.28 123.67 121.83 106.78 103.50 107.11 103.34 128.48 122.87 128.33 123.21 118.2 120.91 121.31 121.63 132.47 128.66 128.03 126.53 135.9 130.13 127.36 130.49
Table I.3. Peak tibiofemoral angles for the 110° parallel squat trials.
106
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Peak Tibiofemoral Angle - 135° Unloaded 50% 1RM 85% 1RM 151.42 139.18 144.85 132.13 137.96 136.46 148.58 145.25 147.63 132.67 141.05 136.83 139.87 142.82 140.40 148.00 154.08 154.48 135.11 137.76 134.73 141.22 146.91 144.19 148.55 152.41 147.83 132.97 126.69 126.50 145.99 140.67 132.74 124.25 130.55 125.04 141.44 137.48 137.25 127.51 130.49 130.01 140.16 154.43 145.77 148.37 150.82 153.15
Table I.4. Peak tibiofemoral angles for the 135° below parallel squat trials.
107
Subject
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Peak External Knee Flexion Moments - 90° (Nm) 50% 85% 50% 135 85% 135° Unloaded 1RM 1RM 1RM 1RM 94.69 134.23 156.08 138.59 151.57 106.93 110.92 155.66 115.11 133.47 135.72 163.85 183.25 170.12 186.78 90.20 146.07 171.81 156.59 166.11 156.30 229.96 234.01 230.60 231.63 116.96 159.99 194.81 151.79 158.91 96.06 146.78 189.23 133.09 165.10 101.99 172.18 191.00 159.45 197.29 93.87 165.49 197.07 135.49 180.48 98.44 171.78 201.90 141.43 190.44 81.94 114.04 153.74 118.59 121.39 93.04 121.34 160.26 124.52 133.68 114.01 172.11 174.77 138.23 169.86 91.56 164.54 187.54 147.49 192.95 99.50 140.74 149.47 133.94 144.28 88.79 126.38 155.61 126.10 144.78
Table I.5. Peak external knee flexion moments (Nm) for the 90° above parallel squat trials.
108
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Peak External Knee Flexion Moments - 110° (Nm) 50% 85% 50% 135 85% 135° Unloaded 1RM 1RM 1RM 1RM 105.25 133.62 152.86 140.60 148.23 97.20 141.75 194.72 167.47 194.40 144.71 201.31 185.21 187.44 225.30 102.01 184.18 193.23 184.18 176.29 182.93 313.54 281.06 315.53 371.16 132.20 174.72 175.38 183.18 190.49 123.63 170.70 183.17 161.00 179.47 94.50 158.79 203.18 154.95 173.42 136.40 168.46 184.64 162.97 176.99 105.59 210.05 223.61 201.25 226.37 94.38 128.64 177.07 130.09 156.74 102.60 156.86 175.24 157.44 168.10 147.82 196.92 215.93 189.80 205.59 115.21 197.25 241.77 203.36 245.23 104.44 152.50 172.34 160.38 189.08 99.49 155.87 171.23 138.19 185.44
Table I.6. Peak external knee flexion moments (Nm) for the 110° parallel squat trials.
109
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Peak External Knee Flexion Moments - 135° (Nm) Unloaded 50% 1RM 85% 1RM 119.18 153.62 177.97 119.36 159.83 203.30 123.97 271.30 325.70 113.46 224.97 241.59 214.78 384.28 408.16 144.85 226.86 262.35 129.63 207.81 217.34 100.41 170.35 193.68 126.34 197.69 219.97 130.37 223.50 278.84 95.86 157.94 172.09 108.08 214.34 234.49 172.48 218.59 242.67 123.63 217.16 270.96 117.71 190.27 233.12 124.31 200.10 258.42
Table I.7. Peak external knee flexion moments (Nm) for the 135° below parallel squat trials.
110
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 99.34 102.50 108.16 95.53 102.86 103.13 90.53 88.50 102.34 92.42 102.33 87.19 102.11 88.78 104.00 107.15
Angle at Peak Moment - 90° 50% 135 50% 1RM 85% 1RM 1RM 79.90 85.09 89.36 78.91 85.09 94.72 91.51 75.04 81.92 87.72 90.45 97.35 108.20 99.43 111.32 90.94 79.22 100.03 95.51 79.96 92.56 104.10 85.72 79.85 102.74 92.61 100.26 91.91 89.09 91.22 95.04 97.30 100.93 71.61 66.95 81.75 101.51 96.52 91.13 87.22 85.58 88.35 103.42 93.06 109.52 98.43 95.29 99.37
Table I.8. Angles at peak moments for 90° above parallel squat trials.
111
85% 135° 1RM 81.73 90.65 81.77 95.54 102.67 96.21 91.30 94.04 96.16 85.94 83.78 81.51 87.59 88.45 100.94 106.07
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 114.19 114.74 130.55 112.64 124.61 130.53 118.95 92.84 134.59 95.25 119.35 101.00 129.01 115.49 130.21 122.83
Angle at Peak Moment - 110° 50% 135 50% 1RM 85% 1RM 1RM 120.67 89.42 125.14 112.89 108.90 116.48 124.40 133.22 124.29 121.56 116.38 121.56 128.41 119.42 127.27 132.33 91.64 136.02 118.40 104.60 119.36 103.83 79.88 131.84 131.82 123.77 122.08 113.36 106.47 113.16 116.37 120.70 123.14 105.28 103.44 103.85 126.27 122.07 123.30 112.99 117.94 116.83 128.49 127.02 127.31 134.92 129.02 126.71
Table I.9. Angles at peak moments for 110° parallel squat trials.
112
85% 135° 1RM 118.36 113.12 120.68 112.61 130.90 130.48 115.45 89.78 120.31 105.58 121.83 101.96 116.34 118.53 125.63 128.31
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Angle at Peak Moment - 135° Unloaded 50% 1RM 85% 1RM 137.18 136.18 141.37 126.99 135.31 135.50 131.18 142.79 145.93 123.91 139.75 132.72 133.90 139.73 137.46 143.73 151.34 152.20 129.20 133.03 130.75 138.52 145.14 83.96 138.05 149.79 144.28 129.74 121.39 125.25 140.36 136.34 125.08 116.03 125.17 121.95 135.42 132.65 134.40 123.97 127.16 127.36 139.56 151.36 144.26 144.21 148.63 151.53
Table I.10. Angles at peak moments for 135° below parallel squat trials.
113
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 2.47 2.45 2.43 2.50 2.45 2.45 2.56 2.59 2.45 2.54 2.45 2.61 2.45 2.58 2.44 2.43
Effective Quadriceps Lever Arms - 90° (cm) 50% 135 50% 1RM 85% 1RM 1RM 2.73 2.64 2.58 2.75 2.64 2.51 2.55 2.82 2.69 2.60 2.56 2.49 2.43 2.47 2.42 2.56 2.74 2.47 2.51 2.73 2.54 2.44 2.63 2.73 2.45 2.54 2.47 2.54 2.58 2.55 2.51 2.49 2.46 2.90 3.01 2.69 2.46 2.50 2.55 2.60 2.63 2.59 2.45 2.53 2.43 2.48 2.51 2.47
85% 135° 1RM 2.69 2.56 2.69 2.50 2.45 2.50 2.55 2.52 2.50 2.62 2.66 2.70 2.60 2.59 2.46 2.44
Table I.11. Effective quadriceps lever arms (cm) for the 90° above parallel squat trials.
114
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Effective Quadriceps Lever Arms - 110° (cm) 50% 135 85% 135° Unloaded 50% 1RM 85% 1RM 1RM 1RM 2.42 2.43 2.57 2.44 2.42 2.42 2.42 2.43 2.42 2.42 2.46 2.44 2.46 2.44 2.43 2.42 2.43 2.42 2.43 2.42 2.44 2.45 2.42 2.44 2.46 2.46 2.46 2.55 2.47 2.45 2.42 2.42 2.44 2.42 2.42 2.53 2.45 2.73 2.46 2.57 2.47 2.46 2.43 2.43 2.43 2.51 2.42 2.43 2.42 2.44 2.42 2.42 2.43 2.43 2.43 2.46 2.44 2.45 2.45 2.46 2.45 2.44 2.43 2.43 2.42 2.42 2.42 2.42 2.42 2.42 2.45 2.45 2.44 2.44 2.44 2.43 2.47 2.45 2.44 2.45
Table I.12. Effective quadriceps lever arms (cm) for the 110° parallel squat trials.
115
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Effective Quadriceps Lever Arms - 135° (cm) Unloaded 50% 1RM 85% 1RM 2.48 2.47 2.48 2.44 2.47 2.47 2.46 2.48 2.48 2.43 2.48 2.46 2.47 2.48 2.48 2.49 2.47 2.47 2.45 2.46 2.46 2.48 2.49 2.66 2.48 2.48 2.49 2.45 2.43 2.44 2.48 2.47 2.44 2.42 2.44 2.43 2.47 2.46 2.47 2.43 2.44 2.44 2.48 2.47 2.49 2.49 2.48 2.47
Table I.13. Effective quadriceps lever arms (cm) for the 135° below parallel squat trials.
116
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 3829.35 4360.51 5587.98 3600.81 6378.95 4776.22 3752.05 3942.63 3826.52 3879.27 3340.13 3571.12 4645.00 3544.68 4070.52 3651.23
Quadriceps Force (N) - 90° 50% 135 50% 1RM 85% 1RM 1RM 4923.18 5918.63 5381.59 4040.42 5902.70 4580.71 6430.00 6489.86 6324.44 5622.97 6708.17 6292.44 9468.53 9466.11 9519.11 6261.56 7111.61 6150.85 5859.06 6943.27 5248.03 7045.22 7269.82 5846.17 6752.21 7772.63 5493.88 6753.73 7829.07 5542.58 4543.88 6176.86 4817.34 4184.99 5322.75 4624.06 7001.85 7002.56 5414.85 6316.54 7132.27 5696.98 5750.85 5906.94 5522.12 5096.61 6206.27 5100.06
Table I.14. Quadriceps force (N) for the 90° above parallel squat trials.
117
85% 135° 1RM 5627.82 5216.32 6936.99 6631.42 9449.32 6359.92 6472.65 7829.29 7221.87 7257.81 4566.61 4956.39 6534.11 7456.90 5861.07 5944.46
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 4348.21 4015.64 5894.11 4213.24 7507.49 5384.72 5100.11 3730.97 5526.76 4210.65 3892.45 4168.56 6033.14 4759.33 4255.82 4091.01
Quadriceps Force (N) - 110° 50% 135 50% 1RM 85% 1RM 1RM 5505.38 5937.54 5766.69 5855.00 8023.40 6916.62 8263.79 7517.31 7695.39 7582.72 7980.76 7582.72 12806.99 11591.03 12907.38 7099.70 6886.65 7409.83 7044.18 7502.02 6639.97 6493.86 7451.05 6300.40 6849.91 7584.81 6706.25 8677.03 9186.62 8313.18 5313.09 7295.42 5347.56 6432.21 7160.87 6438.91 8065.58 8885.65 7800.72 8147.64 9979.41 8397.94 6228.42 7052.16 6560.32 6313.15 6988.50 5656.96
Table I.15. Quadriceps force (N) for the 110° parallel squat trials.
118
85% 135° 1RM 6117.06 8030.15 9282.68 7281.11 15110.49 7759.48 7413.96 6748.49 7294.40 9287.19 6451.41 6846.28 8491.35 10119.03 7750.54 7575.56
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Quadriceps Force (N) - 135° Unloaded 50% 1RM 85% 1RM 4814.96 6212.99 7166.27 4884.40 6470.56 8228.57 5045.13 10918.07 13107.72 4660.10 9068.13 9811.97 8710.01 15489.86 16485.29 5828.15 9180.87 10634.99 5289.40 8436.65 8850.01 4051.42 6854.35 7294.23 5099.86 7980.95 8850.34 5315.77 9202.93 11435.09 3862.28 6386.58 7058.75 4464.31 8790.81 9650.51 6981.78 8878.65 9834.96 5077.47 8884.61 11082.87 4745.36 7700.38 9379.43 5001.54 8067.32 10461.75
Table I.16. Quadriceps force (N) for the 135° below parallel squat trials.
119
Constant k - 90° Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded
50% 1RM
85% 1RM
1.13 1.13 1.14 1.12 1.13 1.13 1.11 1.11 1.13 1.12 1.13 1.10 1.13 1.11 1.13 1.14
1.08 1.08 1.12 1.11 1.14 1.11 1.12 1.13 1.13 1.12 1.12 1.04 1.13 1.10 1.13 1.13
1.10 1.10 1.06 1.11 1.13 1.08 1.08 1.10 1.12 1.11 1.13 1.02 1.13 1.10 1.12 1.12
50% 135 1RM 1.11 1.12 1.09 1.13 1.14 1.13 1.12 1.08 1.13 1.11 1.13 1.09 1.11 1.11 1.14 1.13
Table I.17. Constant k (JRFpf / Fq) for the 90° above parallel squat trials.
120
85% 135° 1RM 1.09 1.11 1.09 1.12 1.13 1.12 1.11 1.12 1.12 1.10 1.09 1.09 1.11 1.11 1.13 1.13
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 1.13 1.13 1.11 1.13 1.12 1.11 1.13 1.12 1.09 1.12 1.13 1.13 1.11 1.13 1.11 1.12
50% 1RM 1.13 1.13 1.12 1.13 1.11 1.10 1.13 1.13 1.10 1.13 1.13 1.13 1.12 1.13 1.11 1.09
Constant k - 110° 85% 50% 135 1RM 1RM 1.11 1.12 1.14 1.13 1.10 1.12 1.13 1.13 1.13 1.12 1.12 1.09 1.13 1.13 1.08 1.10 1.12 1.13 1.14 1.13 1.13 1.12 1.13 1.13 1.13 1.12 1.13 1.13 1.12 1.12 1.11 1.12
85% 135° 1RM 1.13 1.13 1.13 1.13 1.11 1.11 1.13 1.11 1.13 1.13 1.13 1.13 1.13 1.13 1.12 1.11
Table I.18. Constant k (JRFpf / Fq) for the 110° parallel squat trials.
121
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 1.09 1.12 1.11 1.12 1.10 1.06 1.11 1.08 1.08 1.11 1.07 1.13 1.09 1.12 1.08 1.06
Constant k - 135° 50% 1RM 1.09 1.09 1.06 1.08 1.08 1.02 1.10 1.05 1.03 1.13 1.09 1.12 1.10 1.12 1.02 1.04
85% 1RM 1.07 1.09 1.05 1.10 1.09 1.02 1.11 1.09 1.06 1.12 1.12 1.13 1.10 1.11 1.06 1.02
Table I.19. Constant k (JRFpf / Fq) for the 135° below parallel squat trials.
122
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 4324.03 4938.72 6345.32 4045.00 7226.77 5412.07 4175.64 4367.40 4333.38 4334.02 3782.53 3942.97 5259.29 3929.20 4615.06 4145.27
50% 1RM 5317.15 4348.40 7170.73 6216.83 10751.86 6974.59 6581.61 7988.18 7648.96 7537.86 5100.39 4370.59 7923.75 6974.79 6517.76 5748.77
PFJRF (N) - 90° 85% 50% 135 1RM 1RM 6497.95 5973.49 6480.46 5139.00 6880.39 6877.10 7464.20 7087.62 10690.04 10807.83 7662.25 6950.68 7500.47 5864.83 7995.45 6312.90 8686.98 6209.77 8684.71 6177.37 6956.96 5448.70 5431.50 5025.35 7878.22 6033.88 7841.14 6308.46 6607.44 6271.05 6969.20 5759.08
85% 135° 1RM 6115.83 5806.73 7539.51 7449.57 10703.70 7151.93 7215.16 8773.30 8120.61 7987.05 4994.49 5382.30 7221.84 8259.28 6629.29 6746.53
Table I.20. Patellofemoral joint reaction forces (N) for the 90° above parallel squat trials.
123
PFJRF (N) - 110° Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded
50% 1RM
85% 1RM
4931.48 4552.86 6524.36 4781.79 8414.17 5960.79 5761.89 4171.70 6051.43 4727.95 4395.58 4715.21 6702.52 5393.42 4714.78 4598.45
6207.10 6644.46 9265.18 8539.07 14246.95 7823.17 7962.83 7361.81 7558.08 9845.03 6017.04 7297.67 9012.13 9245.85 6927.51 6905.71
6591.50 9111.46 8263.30 9038.09 13088.21 7682.03 8508.53 8046.74 8512.92 10427.60 8224.97 8115.92 9999.12 11286.02 7868.09 7763.71
50% 135 1RM 6457.07 7832.34 8629.51 8539.07 14393.41 8078.10 7498.15 6951.40 7546.51 9433.03 6007.98 7299.61 8761.89 9507.04 7315.01 6315.39
85% 135° 1RM 6915.08 9112.04 10465.72 8263.73 16711.78 8590.66 8401.96 7497.92 8227.88 10538.21 7262.33 7750.71 9616.62 11437.14 8670.65 8429.16
Table I.21. Patellofemoral joint reaction forces (N) for the 110° parallel squat trials.
124
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 5229.74 5449.85 5575.86 5229.12 9556.02 6178.35 5873.72 4380.65 5523.16 5895.63 4148.79 5057.13 7625.58 5696.88 5112.23 5291.44
PFJRF (N) - 135° 50% 1RM 6769.92 7069.58 11618.63 9762.53 16677.22 9391.27 9278.74 7222.85 8229.08 10366.06 6955.56 9842.71 9774.99 9909.73 7876.02 8365.85
85% 1RM 7668.70 8985.14 13764.47 10800.49 17888.91 10829.08 9791.51 7981.98 9360.57 12801.54 7904.67 10861.69 10774.64 12356.56 9920.99 10690.80
Table I.22. Patellofemoral joint reaction forces (N) for the 135° below parallel squat trials.
125
PFJRF (x BW) - 90° Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded
50% 1RM
85% 1RM
5.38 6.59 6.92 4.79 6.86 6.13 4.80 4.93 5.50 5.33 5.31 4.41 6.28 4.58 6.37 5.43
6.61 5.80 7.82 7.36 10.20 7.90 7.56 9.02 9.71 9.28 7.16 4.89 9.47 8.13 9.00 7.52
8.08 8.64 7.50 8.84 10.15 8.68 8.62 9.02 11.03 10.69 9.77 6.07 9.41 9.15 9.13 9.12
50% 135 1RM 7.43 6.85 7.50 8.39 10.26 7.87 6.74 7.12 7.88 7.60 7.65 5.62 7.21 7.36 8.66 7.54
85% 135° 1RM 7.61 7.74 8.22 8.82 10.16 8.10 8.29 9.90 10.31 9.83 7.01 6.02 8.63 9.63 9.16 8.83
Table I.23. Patellofemoral joint reaction forces (x BW) for the 90° above parallel squat trials.
126
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Unloaded 6.13 6.07 7.11 5.66 7.99 6.75 6.62 4.71 7.68 5.82 6.17 5.27 8.01 6.29 6.51 6.02
PFJRF (x BW) - 110° 50% 135 50% 1RM 85% 1RM 1RM 7.72 8.20 8.03 8.86 12.15 10.44 10.10 9.01 9.41 10.11 10.70 10.11 13.52 12.42 13.66 8.86 8.70 9.15 9.15 9.78 8.62 8.31 9.08 7.85 9.59 10.81 9.58 12.12 12.83 11.61 8.45 11.55 8.44 8.16 9.07 8.16 10.77 11.95 10.47 10.78 13.16 11.09 9.57 10.87 10.10 9.04 10.16 8.27
85% 135° 1RM 8.60 12.15 11.41 9.78 15.86 9.73 9.66 8.46 10.44 12.97 10.20 8.66 11.49 13.34 11.98 11.03
Table I.24. Patellofemoral joint reaction forces (x BW) for the 110° parallel squat trials.
127
Subject 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
PFJRF (x BW) - 135° Unloaded 50% 1RM 85% 1RM 6.50 8.42 9.54 7.27 9.43 11.98 6.08 12.67 15.01 6.19 11.56 12.79 9.07 15.83 16.98 7.00 10.64 12.26 6.75 10.66 11.25 4.94 8.15 9.01 7.01 10.45 11.88 7.26 12.76 15.76 5.83 9.77 11.10 5.65 11.00 12.14 9.11 11.68 12.87 6.64 11.56 14.41 7.06 10.88 13.70 6.93 10.95 13.99
Table I.25. Patellofemoral joint reaction forces (x BW) for the 135° below parallel squat trials.
128
