Normative Adductor Squeeze Test Values in Elite Junior Rugby Union ...

ORIGINAL RESEARCH

Normative Adductor Squeeze Test Values in Elite Junior Rugby Union Players Garrett F. Coughlan, PhD,* Eamonn Delahunt, PhD,†‡ Brian M. Caulfield, PhD,§ Colin Forde, BSc,† and Brian S. Green, PhD¶

Objective: To establish normative adductor squeeze test (AST) values in elite junior rugby union players and investigate if differences existed between field position units and categorizations.

Design: Cross-sectional study. Setting: National underage screening camp. Participants: One hundred four healthy players attending an under-19 and under-18 national musculoskeletal and fitness screening camp. Players had no history of surgery, no self-reported history of groin or pelvic pain in either limb and no other lower limb injury in the past 3 months, and no pain reported during the testing procedure.

Main Outcome Measures: The AST in 3 positions of hip flexion (0, 45, and 90 degrees), position unit, and categorizations. Results: The highest AST values were observed at 45 degrees of hip flexion in all field position categories. No differences were observed between position units and categorizations. Conclusions: Normative AST values in an elite junior rugby union population were established in this investigation. Clinically, the sports medicine professional may use these results in making decisions on the management of both symptomatic and asymptomatic players. Key Words: groin injury, rugby union, injury prevention (Clin J Sport Med 2014;24:315–319)

INTRODUCTION

Rugby union is a contact-based field sport in which 2 teams of 15 players of various sizes and statures compete for possession. Players carry, pass, and kick the ball in an attempt to advance toward the opposition’s goal to score as many points as possible. To perform these game tasks safely Submitted for publication December 5, 2012; accepted September 17, 2013. From the *Medical Department, Irish Rugby Football Union, Dublin, Ireland; †School of Public Health, Physiotherapy and Population Science, University College Dublin, Dublin, Ireland; ‡Institute for Sport and Health, University College Dublin, Dublin, Ireland; §School of Public Health, Physiotherapy and Population Science, Health Sciences Centre, University College Dublin, Dublin, Ireland; and ¶USA Rugby, Denver, Colorado. The authors report no conflicts of interest. Corresponding Author: Garrett F. Coughlan, PhD, Medical Department, Irish Rugby Football Union, 10-12 Lansdowne Rd, Ballsbridge, Dublin 4, Ireland ([email protected]). Copyright © 2014 by Lippincott Williams & Wilkins

Clin J Sport Med Volume 24, Number 4, July 2014

and effectively, players must possess adequate strength and endurance of the lower extremities and trunk musculature. Previous research has shown that lower extremity injuries in adolescent rugby union players can range from 25.3% to 44.7% of all injuries with a progressive increase in injury incidence from under-12’s up to under-19’s level.1 Groin injury is particularly prevalent in sports that involve kicking, sprinting, and twisting movements, as these are actions that can overload numerous anatomical structures in the area.2 It is a complex condition whereby multiple pathologies can coexist, and it has been reported that 33% of the injured athletes present with either secondary or tertiary groin-related clinical entities.3 The evaluation and treatment of groin pain in athletes is challenging,4 and these injuries are prone to recurrence that can lead to chronic disability and prolonged recovery if not managed accordingly.5 Weakness of the hip adductor muscles is a risk factor for the development of groin injury in soccer6 and ice hockey7 players. The hip adductors are continuously active throughout running gait and function to stabilize the pelvis (with respect to the thigh) during stance and vice versa during swing phases, respectively.8 It has been reported that bilateral adductor muscle strength is reduced in the period proceeding and during the onset of groin pain in elite junior Australian Rules football players.9 Moreover, differences in the motor control strategies employed by athletes with chronic groin pain may cause inefficient load transfer and altered stress to be attenuated across the pubic symphysis and the development of pain and other associated symptoms in regions such as the lumbar spine and sacroiliac joint.10 Various methods of assessing adductor muscle strength have been purported including hand-held dynamometry,9,11,12 manual muscle testing devices,13 and isokinetic dynamometry.14,15 In the medical literature, only interventions that involve strengthening of the adductor muscles have proved successful in rehabilitation of athletes with groin pathology.3,13,16 Pain provocation on squeeze tests has been shown to be associated with long-standing groin pain17 and to discriminate between athletes with and without current groin pain.18 A number of studies have advocated the use of modified versions of the adductor squeeze test (AST) for the assessment and screening of groin pain in soccer,11,19 Gaelic games,20 and Australian Rules football.17,18,21 The measurement of adductor squeeze values using a sphygmomanometer has previously been reported in the literature,18,20,21 and Delahunt et al20 have reported pressure values and electromyographic activity during this test in 3 hip flexion positions www.cjsportmed.com |

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(0, 45, and 90 degrees). This version of the test has been found to have excellent intrarater reliability among asymptomatic Gaelic games athletes22 and acceptable intrarater and interrater reliability among a mixed cohort of symptomatic and asymptomatic elite junior Australian Rules footballer and soccer players.18 The development of appropriate screening tools may be a crucial component in the prevention of lower extremity injuries.23 The objectives of this study were to establish normative AST values in elite junior rugby union players and investigate if differences existed between field position units and categorizations. These values may assist the sports medicine clinician in the determination of the physical status of a player and facilitate the design of groin injury prevention and management programs in a clinical setting.

METHODS Subjects Subjects were recruited from under-19 and under-18 national team squads who were participating in a musculoskeletal and fitness screening camp.

Ethical Considerations Ethical approval was granted by the local university’s Human Research Ethics Committee. Players under the age of 18 had their consent forms cosigned by their parents/guardian.

Procedures Recruitment was undertaken by forwarding potential subjects an invitation letter containing a participant information leaflet outlining the test procedure and an informed consent form. Inclusion criteria were selection for the national underage panel, no history of surgery, no self-reported history of groin or pelvic pain in either limb and no other lower limb injury in the past 3 months, and no pain reported during the testing procedure. Players were categorized into position units (ie, forwards and backs), and these units were further subdivided into position categorizations (ie, forwards: front row, second row, back row and backs: scrum-half, out-half, centre, wing, full-back).

Outcome Measures The AST protocol undertaken was the same as that previously described.20,22 All participants wore shorts and were barefooted. Immediately before formal testing, each participant was familiarized with the protocol by informing them of the test procedure and allowing them to perform 3 submaximal efforts in each of the test positions, that is, 0, 45, and 90 degrees of hip flexion. For the testing session, participants were again informed of the test procedure. They were then positioned supine with their head flat on the bed and arms across the chest. Each participant was required to perform 3 maximal squeezes in 0, 45, and 90 degrees of hip flexion. The order of the test positions was randomized by assigning each position a number, that is, 1 = 0 degrees, 2 = 45 degrees, and 3 = 90 degrees with the participant asked to select a number between 1 and 3 before testing. The position of hip flexion

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was verified using a goniometer centered over the femoral head and aligned with the middle axillary line and center of the knee joint. The hip joints were kept in neutral internal/ external rotation throughout testing. The AST values were measured using a sphygmomanometer (Welch Allyn Disytest, Skaneateles, New York). The sphygmomanometer was preinflated to 10 mm Hg before each maximal effort. The cuff was positioned so that the middle third was placed on the most prominent point of the medial femoral condyles. Participants were instructed to squeeze the cuff as hard as possible. The highest pressure value obtained for each maximal squeeze was recorded visually on the sphygmomanometer dial by the tester. Trials were considered invalid and repeated if any of the following occurred: the participants’ head lifted off the bed, hands were removed from the chest, the pressure cuff slipped, or the participant pushed through heels/feet. Participants were allowed a 15-second rest between maximal squeezes and 45-second rest between each test position. Participants were unable to see the sphygmomanometer and were unaware of test scores for the duration of the testing session.

Analysis Statistical analysis was undertaken using SPSS Statistics 20 (IBM Ireland Ltd, Dublin, Ireland). The average of 3 trials for each test position was used for statistical analysis. A 2-way between-groups analysis of variance (ANOVA) was conducted to explore the impact of position unit (ie, forward or back) and hip joint position (0, 45, and 90 degrees) on AST values. A 1-way between-groups multivariate analysis of variance (MANOVA) was conducted to investigate the effect of position categorization on AST values. Three dependent variables were used: AST values at 0, 45, and 90 degrees of hip joint flexion. The independent variable was position categorization.

RESULTS A total of 104 players participated in the study (age, 17.56 6 0.54 years; height, 1.83 6 0.06 m; body mass, 91.60 6 8.74 kg; Table 1). Results of the 2-way between-groups ANOVA were as follows: the interaction effect between position

TABLE 1. Mean Age, Height, and Body Mass of Participants Position Categorizations Front row (n = 17) Hooker (n = 7) Second row (n = 13) Back row (n = 22) Out-half (n = 8) Scrum-half (n = 6) Center (n = 9) Wing (n = 13) Full-back (n = 9) Overall (n = 104)

Age 17.70 17.46 17.50 17.68 17.19 17.45 17.75 17.63 17.30 17.56

6 6 6 6 6 6 6 6 6 6

Height 3.58 2.63 5.15 0.61 3.79 4.24 3.99 8.08 3.20 0.54

1.83 1.78 1.93 1.86 1.80 1.72 1.85 1.81 1.79 1.83

6 6 6 6 6 6 6 6 6 6

0.04 0.02 0.05 0.05 0.05 0.04 0.04 0.06 0.03 0.06

Body Mass 104.43 91.34 98.14 91.51 81.53 74.77 87.07 85.68 81.16 91.60

6 6 6 6 6 6 6 6 6 6

7.93 7.02 5.05 8.51 6.15 7.65 6.18 7.73 4.57 8.74

Values are given as mean 6 SD.

Ó 2014 Lippincott Williams & Wilkins


unit and hip joint position was not statistically significant, F(2,306) = 0.15, P = 0.86. There was a statistically significant main effect for hip joint position, F(2,306) = 20.59, P , 0.01. The associated effect size was moderate (partial eta squared = 0.11). Post hoc comparisons using the Tukey honestly significant difference test indicated that the 45-degrees hip joint flexion position (228.28 6 37.92 mm Hg) differed significantly from the 0-degree hip joint flexion position (214.53 6 36.08 mm Hg) and 90-degree hip joint flexion position (195.11 6 37.81 mm Hg). The 0-degree hip joint flexion position (214.53 6 36.08 mm Hg) also differed significantly from the 90-degree hip joint flexion position (195.11 6 37.81 mm Hg; Table 2). The main effect for position unit did not reach statistical significance, F(1,306) = 0.03, P = 0.84, partial eta squared = 0.00. Results of the 1-way between-groups MANOVA were as follows: no significant difference was observed between the position categorizations on the combined dependent variables, F(24,270) = 1.26, P = 0.18, Wilk Lambda = 0.73, partial eta squared = 0.09 (Table 3).

DISCUSSION

The principle finding of this study was that asymptomatic elite junior rugby union players have the highest AST values at 45 degrees of hip flexion in all field position categories. This study has established normative values of AST in this player population and is the first study to report these values in rugby union. The results of this study may assist the sports medicine clinician in making key decisions regarding the management of both symptomatic and asymptomatic players. Owing to the multiplanar function of the hip adductors, these muscles have an essential role in motor control and stability of the lower kinetic chain during the gait cycle. Ancillary to their action as hip adductors in the frontal plane,

AST Values in Junior Rugby Players

they also act as an accessory hip flexor up to 90 degrees of hip flexion and an accessory hip extensor at angles greater than this in the sagittal plane.24,25 In the transverse plane, they eccentrically control femoral internal rotation during the loading response, as well as producing external rotation during terminal stance and preswing.26 In this study, we observed peak squeeze values in the 45-degree hip flexion position and a statistically significant difference in this position compared with values obtained in the 0 and 90 degrees. Despite different sporting codes and player profiles, these results are in line with recent findings by our research group in Gaelic games players, in which we also recorded that the position of 45 degrees of hip flexion produced the greatest amount of adductor muscle activity using electromyography (EMG) compared with 0 and 90 degrees.20 Lovell et al27 suggest that the clinician should assess strength of the gracilis, adductor longus, and adductor magnus muscles in 45-degree hip flexion based on peak EMG output obtained for these muscles in the 0-, 45-, and 90-degree hip flexion positions. During the stance phase of the gait cycle, motion at the hip joint ranges from 50 degrees of hip flexion at initial contact to 5 degrees of hip extension at toe off28 and the hip adducts relative to the pelvis as the ground reaction force falls medial to the knee.29 Therefore, we have previously postulated that 45 degrees of hip flexion represented the optimal position to elicit adductor muscle activity in the AST, as it is in a similar range to the lower limb as it begins to absorb dynamic weight bearing load.20 The results of this study support these previous findings. Studies in other sports have reported lower squeeze test values than those recorded in this study; however, they included both symptomatic and asymptomatic participants18,21 (Table 3), whereas we included only asymptomatic individuals who experienced no pain during the test procedure. We observed lower squeeze values in both the 0 and 90 degrees of hip flexion position in this study and in earlier

TABLE 2. Mean Pressure Values for Group, Position Units, and Categorizations for the 3 Testing Positions Group mean Position units Forward Back Position categorizations Front row Hooker Second row Back row Out-half Scrum-half Center Wing Full back

0 degree

45 degrees

90 degrees

214.53 6 36.08*†

228.28 6 37.92*‡

195.11 6 37.81†‡

213.86 6 36.29 215.41 6 36.22

228.28 6 39.25 228.29 6 36.53

196.85 6 33.11 192.83 6 43.46

195.33 193.05 238.41 220.30 204.83 217.56 232.07 220.15 199.89

6 6 6 6 6 6 6 6 6

30.79 20.27 34.16 35.97 30.78 31.52 23.96 46.49 34.89

205.20 225.29 243.90 237.85 214.25 223.39 240.70 237.79 217.93

6 6 6 6 6 6 6 6 6

43.95 34.58 30.88 34.88 22.95 32.81 25.54 48.14 37.74

184.67 194.57 207.00 201.00 174.33 192.78 194.70 208.31 185.11

6 6 6 6 6 6 6 6 6

33.14 35.78 29.90 33.42 39.36 27.30 37.94 53.25 45.54

Pressure values (in mm Hg). Values are given as mean 6 SD. *Significantly different from 90 degrees. †Significantly different from 45 degrees. ‡Significantly different from 0 degree.


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TABLE 3. Studies Using the Adductor Squeeze Test With a Sphygmomanometer Hip Flexion Position and Squeeze Value, degree

Authors and Year

Sample Size

Present study

104

Rugby union

Delahunt et al, 201122

18

Gaelic games

Taylor et al21

270

Australian Rules football

29

Australian Rules football

Malliaras et al18,†

Sport

Status

Demographics

0

45

90

Age, 17.56 6 0.54 y 214.53 6 36.09 228.28 6 37.92 195.11 6 37.81 Height, 1.83 6 0.06 m Body mass, 91.60 6 8.74 kg Asymptomatic only Age, 21.11 6 2.53 y 202.2 6 57.28 236.76 6 47.29 186.11 6 44.08 Height, 1.78 6 0.06 m Body mass, 78.24 6 11.76 kg Asymptomatic and Age, 16.7 (14-21) y 187.57 6 42.56 NA 176.94 6 62.32 symptomatic* Height, 1. 83 (1.68-2.04) m Body mass, 76.05 (64-104.8) kg 19 Asymptomatic Age, 17.2 6 1.2 y 210.8 6 39.3 209.6 6 42.3 NA and 10 symptomatic Height, 1.84 6 0.07 m Body mass, 77.8 6 6.2 kg

Asymptomatic only

Pressure values (in mm Hg). Values are given as mean 6 SD. NA, not assessed. *Exact numbers of each not reported. †Data average between test and retest.

work.20 The 0 degree of hip flexion position corresponds closely with maximal hip extension at the terminal stance phase of the gait cycle, and the 90 degrees of hip flexion position is similar to the range of motion achieved by elite sprinters towards terminal swing phase of the gait cycle.28 Peak EMG output for the pectineus muscle has been reported at 90 degrees of hip flexion.27 The lower values observed in this range may result from the reduced ability of the adductors to produce force in the frontal plane in this range compared with 0 and 45 degrees of hip flexion because they change their orientation to simultaneously work in the sagittal plane as secondary hip flexors and extensors. Although we observed lower values in the 0 and 90 degrees of hip flexion positions, we recommend that the AST is conducted in all 3 test positions to ascertain differences that may occur in these ranges because of the aforementioned multifunctional role of the adductor muscles throughout these movements. These values may influence the ranges of hip motion in which strengthening exercises are conducted, as well as providing the ability to monitor a player’s functional response to loading in these positions. For example, a recent study reported reductions in the ratio of gluteus medius and adductor longus activity in the injured stance leg of chronic groin injured Gaelic games and soccer players compared with uninjured controls during a standing hip flexion test to 90 degrees of hip flexion position.10 This was primarily because of the reduction not only in gluteus medius activation but also the adductor longus. Thus, the importance of integrating coactivation exercises to stabilize the lumbopelvic and hip complex in a range of hip positions in athletes with groin pain is essential to prepare them for sport-specific activities. Previous research has detected a decrease in adductor muscle strength in the weeks preceding the onset of groin injury among previously asymptomatic elite junior Australian Rules football players when using a hand-held dynamometer to

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measure AST values.9 A comparison between pre-season and in-season values against the normative values in this study may be a valuable method of early identification and prevention of groin injury in a junior rugby union population. Varying physical capacities and anthropometric profiles are required for different playing positions in rugby union. We observed no statistically significant differences between the position units and categorizations in squeeze test values; however, further data with a larger sample size may lead to significant findings. This suggests that player size in this junior population does not influence these values; however, because players’ transition to senior level and greater disparity exists between physical profiles, this may become more apparent. Previous research has shown a correlation between higher force values and body mass index in elite junior soccer players.27 The highest squeeze values were observed in second rows in 45 degrees of hip flexion (243.90 6 30.88 mm Hg) and the lowest by the out-halfs in 90 degrees of hip flexion (174.33 6 39.36 mm Hg). Despite the small sample of out-halfs in the study, this low value is of note as it may be influenced by the repeated kicking activity associated with this field position categorization. This may result in overuse of the adductor muscle group and therefore potentially result in a higher risk of injury in this group. Further research in a larger sample of this field position categorization is required. A limitation of this study is that no EMG analysis of the adductor muscles was undertaken to determine what muscles had the greatest activity in rugby union players in each of the hip flexion positions. The results in this study represent the normative strength values for elite junior rugby union players only and cannot be considered to be normative values for other athletic populations. Future studies in senior level players and in a larger population are now required. The authors of this study recommend that standard units of measurement (ie, mm Hg) be used in studies assessing AST Ó 2014 Lippincott Williams & Wilkins


to allow for standardization and comparison of values between different athletic populations.

CONCLUSIONS With the increasing demands of the professional game, comprehensive injury prevention and rehabilitation to maximize player training and game time is imperative. The design of a rehabilitation program that safely challenges an injured player to prepare for the demands of rugby union is essential before return to play from injury.30 This study has established normative values for the AST in an elite junior rugby union population. These findings have implications for the design of groin injury prevention and management strategies. This test is also easy to apply and is an economical method of testing for rugby union teams. REFERENCES 1. Bleakley C, Tully M, O’Connor S. Epidemiology of adolescent rugby injuries: a systematic review. J Athl Train. 2011;46:555–565. 2. Falvey EC, Franklyn-Miller A, McCrory PR. The groin triangle: a pathoanatomical approach to the diagnosis of chronic groin pain in athletes. Br J Sports Med. 2009;43:213–220. 3. Hölmich P. Long-standing groin pain in sportspeople falls into three primary patterns, a “clinical entity” approach: a prospective study of 207 patients. Br J Sports Med. 2007;41:247–252. 4. Tyler TF, Silvers HJ, Gerhardt MB, et al. Groin injuries in sports medicine. Sports Health. 2010;2:231–236. 5. Werner J, Hägglund M, Waldén M, et al. UEFA injury study: a prospective study of hip and groin injuries in professional football over seven consecutive seasons. Br J Sports Med. 2009;43:1036–1040. 6. Engebretsen AH, Myklebust G, Holme I, et al. Intrinsic risk factors for groin injuries among male soccer players: a prospective cohort study. Am J Sports Med. 2010;38:2051–2057. 7. Tyler TF, Nicholas SJ, Campbell RJ, et al. The association of hip strength and flexibility with the incidence of adductor muscle strains in professional ice hockey players. Am J Sports Med. 2001;29:124–128. 8. McClay IS, Lake MJ, Cavanagh PR. Muscle activity in running. In: Cavanagh PR, ed. Biomechanics of Distance Running. Champaign, IL: Human Kinetics Books; 1990:165–186. 9. Crow JF, Pearce AJ, Veale JP, et al. Hip adductor muscle strength is reduced preceding and during the onset of groin pain in elite junior Australian football players. J Sci Med Sport. 2010;13:202–204. 10. Morrissey D, Graham J, Screen H, et al. Coronal plane hip muscle activation in football code athletes with chronic adductor groin strain injury during standing hip flexion. Man Ther. 2012;17:145–149. 11. Hanna CM, Fulcher ML, Elley CR, et al. Normative values of hip strength in adult male association football players assessed by handheld dynamometry. J Sci Med Sport. 2010;13:299–303.


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