Effect of Ankle Taping and Bracing on Vertical Ground ...

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Effect of Ankle Taping and Bracing on Vertical Ground Reaction Forces During Drop Landings Before and After Treadmill Jogging

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Shipping/Billing Bryan L. Riemann,Information PhD, ATC1 Randy J. Schmitz, PhD, ATC2 Name _______________________________________________________________________________________________ Michael Gale, MS, ATC3 Address Steven _____________________________________________________________________________________________ T. McCaw, PhD4 Address _____________________________________________________________________________________________ City _______________________________State/Province __________________Zip/Postal Code _____________________ Phone _____________________________Fax____________________________Email _____________________________ Study Design: Single-group repeated-measures experimental design. he large number of Objectives: The purpose of this study was to evaluate the effects of prophylactic ankle inversion ankle sprains Would you like to receive JOSPT email updates and renewal notices? Yes No stabilization on vertical ground reaction forces before and after treadmill jogging. sustained by physically Background: Previous research has demonstrated acute effects of ankle taping and bracing on active persons has ankle joint kinematics and vertical ground reaction forces during drop landings. Based on the prompted researchers Payment Information number of investigations demonstrating increased range of motion of the braced or taped ankle and clinicians to develop and following exercise, it may be plausible that the aforementioned landing alterations may return to adopt preventative strate Check enclosed (made payable to the JOSPT). normal following an exercise bout. gies.4,19,23,25,30,34 One approach Methods and Measures: Fourteen healthy recreational participants performed stiff and soft drop Credit Card (circle one) MasterCard VISA American Express that has received increased attenlandings before and after a 20-minute treadmill exercise bout under 3 different ankle stabilizer tion is prophylactic ankle taping conditions (no stabilizer, ankle brace, and ankle tape). A forceplate was used to collect ground Card Number ___________________________________Expiration Date _________________________________________ and bracing. While the effectivereaction force data under the dominant foot. The first and second peak impact force, as well as ness of prophylactic ankle taping the time to______________________________________Date each of the 2 peak forces, were determined for each trial and used as dependent Signature __________________________________________________ and bracing in reducing the incivariables. dence of injury remains debatable Results: The time to reach peak forces were significantly less under the ankle brace and tape for some authors,34 others advoconditions in comparison to the control (no-stabilizer) condition. To order fax, email mail to:cate their utilization.23,36 Conclusions: It appears that ankle taping and bracing decreasecall, the time to reach peak or impact While some researchers forces. These alterations indicate that during dynamic activity the musculoskeletal structures of the 1111 North Fairfax Street, Suite 100, Alexandria, VA 22314-1436 have considered performancebody may be subjected to loads within shorter time periods. Whether these effects are detrimental Phone 877-766-3450 • Fax 703-836-2210 • Email: [email protected] related consequences,21,26,29 the over time remains speculative at this point and requires further research. J Orthop Sports Phys of ankle-taping and Ther. 2002;32:628–635. Thank you for subscribing! majority ankle-bracing research has Key Words: ankle brace, inversion ankle injury, prevention, prophylactic considered the effects on ankle ankle bracing joint range of motion (ROM).1,2,9,14,18,19,27,29,33,35,37,38 It is the assumption of these investigations that restriction of joint 1 Assistant professor and coordinator, Graduate Athletic Training Program, Georgia Southern University, ROM represents the quantity of Statesboro, GA. stability provided by each appli2 Assistant professor, Department of Exercise and Sport Science, University of North Carolina at ance. Common to both ankle tapGreensboro, Greensboro, GA. 3 Graduate student, Department of Exercise and Sport Science, University of North Carolina at ing and bracing is the concept of Greensboro, Greensboro, GA. restricting excessive ankle inver4 Professor, School of Kinesiology and Recreation, Illinois State University, Normal, IL. sion, while allowing normal ankle This study was approved by the University of North Carolina, Greensboro, Institutional Review Board. Send correspondence to Bryan Riemann, Graduate Athletic Training Program, Georgia Southern dorsiflexion and plantar flexUniversity, Statesboro, GA 30460-8076. E-mail: [email protected] ion.9,14,30 A meta-analysis con-

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kinematic and force changes seen in drop landings, it is plausible that the measures would return to normal as exercise lessens the ROM restrictions. Therefore, the purpose of this study was to evaluate the effects of prophylactic ankle taping and bracing on vertical ground reaction forces before and after treadmill jogging.

METHODS Subjects Fourteen recreationally active, healthy, college students (9 males, 5 females, ages 17–26 years, height [mean ± SD] = 173 ± 8 cm, mass [mean ± SD] = 75 ± 13 kg [735 ± 127 N]) volunteered for this study. All subjects were free of any lower extremity orthopedic-related injuries or neurological disorders as indicated on a medical history questionnaire. Prior to participation, informed consent from each participant was acquired in accordance with the University of North Carolina at Greensboro Institutional Review Board.

Design

Landing Protocol The landing technique previously reported by DeVita and Skelly11 was adopted for this investigation. Subjects stepped off a 0.59-m-high wooden platform placed 0.1 m posterior to the back edge of the landing target, using a standardized takeoff position.

J Orthop Sports Phys Ther • Volume 32 • Number 12 • December 2002

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A single-group repeated-measures experimental design was utilized. Each subject attended 3 testing sessions, with at least 48 hours but no more than 96 hours between test sessions. At each session, 1 of 3 ankle stabilizer conditions was applied by a certified athletic trainer to both ankles: control (no stabilizer), semi-rigid AirSport ankle brace (AirCast, Inc., Summit, NJ) or ankle tape (Coach Athletic Tape, Johnson & Johnson, Skillman, NJ). The ankle taping procedure consisted of a modified Gibney closed basket weave.3 Tape adherent spray (Tuf-Skin, Cramer Inc., Gardner, KS), gel-lubed (Skin-Lube, Cramer, Gardner, KS) heel and lace pads (Heel & Lace Pads, Cramer, Gardner, KS), and foam prewrap (Tape Underwrap, Cramer, Gardner, KS) were applied prior to the tape application. The same certified athletic trainer applied both the ankle braces and tape to each participant. Following application of the stabilizer conditions, each subject was fitted with a pair of standard low-cut laboratory shoes (Mundial Team, Adidas America, Portland, OR). Subjects were asked to complete 6 soft and 6 stiff landings prior to and following a moderate-intensity exercise bout. This resulted in 24 landings completed by each subject during each testing session. The order of stabilizer conditions and landing styles was counterbalanced between subjects.

RESEARCH

ducted by Cordova et al9 collapsed the results of a number of investigations considering ankle joint ROM prior to and following exercise. The results of this meta-analysis revealed that semirigid devices were superior to lace-up orthosis and tape for restricting ankle inversion before and after exercise. The results also demonstrated that dorsiflexion ROM was significantly less in ankles stabilized with tape than in those stabilized with lace-up braces, with no significant change following an exercise bout. Significant increases in plantar flexion ROM were revealed following exercise independent of the stabilizer condition. A lack of data in the literature considering the effect of semirigid braces and exercise on dorsiflexion and plantar flexion ROM precluded inclusion into the meta-analysis. The concern over ankle dorsiflexion and plantar flexion restrictions induced by braces and tape relates to the importance of this motion for shock absorption during landing.28 Significant alterations in sagittal plane ankle joint kinematics during drop landings have been documented.28 Specifically, reduced ankle plantar flexion at ground contact, reduced dorsiflexion during the impact phase of ground contact, and decreased maximum ankle velocity were revealed during testing of several ankle braces and tape. These alterations led to the hypothesis that some ankle orthoses may reduce the ability of the ankle to absorb energy, and thereby increase the dissipation demands of the knee and hip joints.28 This hypothesis parallels the speculation that the effective protection of the lower leg and ankle by ski boots promotes direct translation of the forces to the knee,22 thereby explaining the high incidence of knee injury in skiers. Providing direct support for the notion of altered body impact absorption are the results of an investigation comparing vertical ground reaction force during drop landings under control, ankle tape, and combined ankle and brace conditions.8 It was revealed that a tape condition and a tape-spat combination condition led to a significantly higher impact force and a significantly shorter temporal interval to attain the peak impact force than a control condition. Based on the results of the previous study documenting altered sagittal plane ankle kinematics during drop landings,28 the measured impact force alterations were attributed to the ankle dorsiflexion being impeded by the tape. An important commonality between the above investigations concerning altered ankle kinematics28 and those concerning vertical ground reaction forces during drop landings8 is the testing being conducted immediately after the application of each stabilizer. As stated previously, a number of investigations have demonstrated increases in ROM following exercise.2,9,18,19 Assuming that ROM restriction by ankle tape and braces is responsible for the reported ankle

This position involved having each subject flex both shoulders to 90° while placing the heel of the dominant foot against the leading edge of the wooden platform. When ready, the subject then leaned forward to step off the platform (Figure 1). This procedure minimized the amount of horizontal motion and allowed subjects to land with their weight equally balanced between the 2 lower extremities. Only the dominant foot, operationally defined as the preferred kicking extremity, contacted the force platform. During a soft landing, a subject was instructed to land with maximal knee flexion while still maintaining heel contact with the force platform. Subjects were instructed to land with minimal knee flexion during a stiff landing. Prior to the application of the stabilizer or data collection, each subject was given a full standardized verbal description and visual demonstration of both landing techniques. Additionally, subjects were given sufficient practice time to become proficient at each landing style. Proficiency was marked by the ability to repeatedly land with simultaneous foot contact in the proper location (only dominant foot on forceplate), using the proper knee flexion strategy. This typically took 4 to 5 landings for each of the landing strategies.

FIGURE 1. Participant assuming the start position for the drop landings. 630

Exercise Bout The 20-minute exercise bout consisted of a treadmill jog, with the intensity and protocol individually determined for each subject during the first testing session. First, 65% and 70% maximum heart rate reserve was calculated using the Karvonen Formula.7 Participants were then given a 3-minute warm-up on the treadmill at 4 km per hour. Following the warmup, the speed of the treadmill (Parker Treadmill Co., Opelika, AL) was recorded and manipulated in 2-minute intervals, such that heart rate remained within the 65% to 70% target range. A Polar heart rate monitor (Polar CIC, Inc., Port Washington, NY) was used for all heart rate measurements. Following 20 minutes, a 2-minute cool-down at 4 km per hour was provided. The protocol used during the first session was duplicated during the 2 subsequent test sessions.

Ground Reaction Force Data A Kistler piezoelectric forceplate (Type 9281B, Kistler Instrumente AG, Winterthur, Switzerland) installed flush with the floor was utilized to collect the vertical ground reaction force (vGRF) data. Data from the forceplate were sampled at 1000 Hz and converted to vGRF data using an acquisition program based on customized LabVIEW software (National Instruments, Austin, TX). Normalization to body weight (BW) in Newtons and smoothing (secondorder Butterworth, 60-Hz cutoff) of the vGRF data were conducted off-line. Only trials that exhibited a bimodal vGRF curve characteristic of a toe-heel landing style were used for data analysis.12 A set of 2 kinetic and 2 temporal variables describing the vGRF profiles was compiled for each trial. These variables consisted of the following: (1) first peak impact force, (2) second peak impact force, (3) time to first peak impact force, and (4) time to second peak impact force (Figure 2).

FIGURE 2. Representative vertical ground reaction force curve from a stiff landing. The 4 variables considered are labeled as follows: FPIF, first peak impact force; TFPIF, time to first peak impact force; SPIF, second peak impact force; TSPIF, time to second peak impact force.


TABLE 1. Correlation ratios (sum squares trial/sum squares total) expressed as percentages across the 6 trials under each stabilizer, time, and landing style condition. Group Control Pre-exercise soft landing Pre-exercise stiff landing Postexercise soft landing Postexercise stiff landing Ankle brace Pre-exercise soft landing Pre-exercise stiff landing Postexercise soft landing Postexercise stiff landing Ankle tape Pre-exercise soft landing Pre-exercise stiff landing Postexercise soft landing Postexercise stiff landing

First Peak Impact Force

Second Peak Impact Force

Time to First Peak Impact Force

Time to Second Peak Impact Force

0.9 4.1 2.8 4.7

2.4 6.5 4.7 1.3

2.1 1.2 3.9 3.6

2.9 3.6 2.7 2.5

1.1 2.8 0.9 5.3

2.3 2.0 1.9 1.2

1.4 1.2 0.8 3.8

1.5 1.7 0.7 3.7

5.6 3.2 2.6 5.9

2.1 2.6 3.0 3.6

2.4 1.4 5.3 3.1

3.5 1.6 5.2 3.9

Data Analysis

The correlational ratios, expressed as percentages, for the dependent variables ranged between 0.9% and 6.5% for peak impact forces and 0.7% to 5.3% for time to reach peak impact forces (Table 1). The first peak impact forces (Table 2) were significantly greater before the exercise bout compared to postexercise values (F1,13 = 6.40, P = 0.025). In addition, the first peak impact forces during the stiff landings were significantly greater compared to those of the soft landings (F1,13 = 19.67, P = 0.001). The

TABLE 2. Means and standard deviations for first peak impact force (units are in number of body weights).*† Pre-exercise Group ‡

Control Ankle brace Ankle tape

Postexercise

Soft Landing

Stiff Landing

Soft Landing

Stiff Landing

1.35 ± 0.35 1.31 ± 0.30 1.30 ± 0.42

1.64 ± 0.33 1.52 ± 0.30 1.44 ± 0.27

1.27 ± 0.28 1.23 ± 0.24 1.19 ± 0.21

1.54 ± 0.30 1.45 ± 0.26 1.39 ± 0.27

*

Values for pre-exercise significantly greater than postexercise values (P⬍0.05) Values for stiff landing significantly greater than soft landing values (P⬍0.05) ‡ No significant differences were found across stabilizer conditions (P⬎0.05) †


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RESULTS

ankle stabilizers had no effect on the first peak impact forces as evidenced by the ANOVA, which revealed no significant interactions for style×stabilizer×time (F2,26 = 0.287, P = 0.753), stabilizer×time (F2,26 = 0.109, P = 0.897), and style×stabilizer (F2,26 = 1.80, P = 0.185), and no significant main effect for stabilizer (F2,26 = 2.62, P = 0.092). Lastly, the interaction for style×time (F1,13 = 0.167, P = 0.689) was not significant. The stabilizer conditions revealed a significant effect (F2,26 = 5.33, P = 0.011) on the time to first peak impact force (Table 3). Post hoc analysis (Tukey’s Honestly Significant Difference [HSD] test = 1.64, P⬍0.05) identified the time to first peak impact force during the no-stabilizer (control) condition to be significantly greater in comparison to the tape and the brace conditions. The results revealed no significant interactions for style×stabilizer×time (F2,26 = 0.849, P = 0.440), stabilizer×time (F2,26 = 0.619, P = 0.546), style×time (F1,13 = 0.875, P = 0.367), and style×stabilizer (F2,26 = 0.589, P = 0.562), and no significant main effects for style (F1,13 = 0.002, P = 0.964) and time (F1,13 = 0.493, P = 0.722). Only landing style (stiff landing greater than soft landing) had a significant effect (F1,13 = 30.38, P⬍0.001) on the second peak impact force (Table 4). Similar to the first peak impact force, the stabilizers did not have a significant effect on the second peak impact forces, as the ANOVA revealed no sig-

RESEARCH

Verification of the participants’ proficiency in performing the landings under each stabilizer, time, and landing condition across the 6 trials was conducted using the correlation ratio between the variance attributable to trial and total variance (␩2 = sum squares trial/sum squares total) for the 4 dependent variables. The mean of the 6 trials was calculated for each landing style (soft and stiff) by stabilizer (control, tape, and brace) and time (pre-exercise and postexercise) conditions. Separate 3-factor repeatedmeasures analyses of variance were used to statistically analyze each variable. Within-subject factors consisted of landing style, stabilizer, and time. Statistical significance was considered at the Pⱕ0.05 level. Where applicable, Tukey post hoc procedures were utilized to identify significant differences identified by the omnibus F tests.

TABLE 3. Means and standard deviations for time to first peak impact force (milliseconds). Pre-exercise Group Control* Ankle brace Ankle tape *

Postexercise

Soft Landing

Stiff Landing

Soft Landing

Stiff Landing

14.4 ± 2.4 12.9 ± 2.1 13.2 ± 2.1

15.1 ± 3.6 12.9 ± 2.1 13.0 ± 1.9

15.1 ± 2.9 13.2 ± 2.4 13.1 ± 3.1

14.9 ± 3.4 13.1 ± 2.3 12.8 ± 2.4

Time significantly greater than for the ankle brace and ankle tape conditions (P⬍0.05)

nificant interactions for style×stabilizer×time (F2,26 = 2.64, P = 0.090), stabilizer×time (F2,26 = 1.64, P = 0.214), and style×stabilizer (F2,26 = 1.25, P = 0.303), and no significant main effect for stabilizer (F2,26 = 1.34, P = 0.277). Lastly, the interaction for style×time (F1,13 = 1.06, P = 0.321) and the main effect for time (F1,13 = 2.74, P = 0.122) were not significant. The stabilizer condition also had a significant effect (F2,26 = 7.94, P = 0.002) on the time to second peak impact force (Table 5). Post hoc analyses identified the time to second peak impact force during the no-stabilizer condition to be significantly longer in comparison to the tape and the brace conditions (Tukey’s HSD = 3.22, P⬍0.05). The results revealed no significant interactions for style×stabilizer×time (F2,26 = 2.61, P = 0.093), stabilizer×time (F2,26 = 0.239, P = 0.789), style×time (F1,13 = 0.065, P = 0.803), and style×stabilizer (F2,26 = 0.204, P = 0.817), and no significant main effects for style (F1,13 = 1.61, P = 0.226) and time (F1,13 = 3.43, P = 0.087).

DISCUSSION The purpose of this investigation was to evaluate the effects of prophylactic ankle stabilization on vertical ground reaction forces before and after treadmill jogging. The time to first and second peak impact forces was reduced significantly under the ankle tape and brace conditions across the soft and stiff landings. These results suggest that ankle tape and brace conditions impose higher stresses on the musculoskeletal system during dynamic activity by

decreasing energy absorption time following ground contact. Another important result was that a bout of moderate-intensity exercise did not alter the effect of ankle support on the vGRF variables. Previous investigations have documented that with ankle support, active and passive ankle dorsiflexion/ plantar flexion ROM return to unsupported levels following exercise,9,29 although the magnitude of change appears to be brace dependent.1,9,17,32 These results have been attributed to a mechanical breakdown of the tape or moisture accumulation under the tape or brace.30 Based on the idea that dorsiflexion/plantar flexion restrictions from acute ankle tape and brace applications were responsible for the previously demonstrated vGRF alterations,8 coupled with the documented ROM increases following exercise, it was hypothesized in the current investigation that the altered vGRF in the tape and brace conditions would resemble the control condition following the exercise bout. The current statistical analyses failed to reveal significant exercise×stabilizer interactions, suggesting exercise had no effect on the dependent variables. But because ankle joint ROM was not measured in this study, it is not known if the exercise bout actually changed the amount of available ankle ROM between the pre-exercise and postexercise testing sessions. Several factors related to the design of this investigation may partly explain the lack of significance

TABLE 4. Means and standard deviations for second peak impact force (units are in number of body weights).* Pre-exercise Group †

Control Ankle brace Ankle tape

Postexercise

Soft Landing

Stiff Landing

Soft Landing

Stiff Landing

3.49 ± 0.95 3.65 ± 1.32 3.58 ± 0.79

4.28 ± 1.05 4.48 ± 1.00 4.92 ± 0.95

3.36 ± 0.78 3.37 ± 1.02 3.55 ± 0.82

4.49 ± 0.99 4.48 ± 1.05 4.66 ± 0.71

* Values for stiff landing significantly greater than soft landing values (P⬍0.05) † No significant differences were found across stabilizer conditions (P⬎0.05) TABLE 5. Means and standard deviations for time to second peak impact force (milliseconds). Pre-exercise Group Control* Ankle brace Ankle tape

Postexercise

Soft Landing

Stiff Landing

Soft Landing

Stiff Landing

43.0 ± 6.4 39.9 ± 7.9 40.4 ± 8.0

42.3 ± 7.9 37.9 ± 5.2 35.9 ± 7.5

44.1 ± 6.8 40.4 ± 8.0 38.8 ± 6.6

42.0 ± 7.3 38.6 ± 6.8 37.9 ± 5.7

* Time significantly greater than for the ankle brace and ankle tape conditions (P⬍0.05) 632



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The specific variables targeted by this investigation were the first and second peak impact force magnitude and timing during the impulse period immediately following ground contact. The importance of this period relates to the absorption and transmission of energy onto the different tissues comprising the musculoskeletal system. Both the impact peak values and loading rates are related to the shock wave transmitted through the body, which is suggested to be associated with impact-related injuries.5,39 Although the dampening characteristics of bone, cartilage, and tissue are associated with impact energy absorption, the kinematic patterns of the body are attributed to having a more potent influence on the vGRF impulse period characteristics.20,24 Generally, impact absorption is considered to occur in a distal-toproximal sequence.20,24 Essential to reducing impact force magnitudes are the joint angles at ground contact,6,13 as well as the utilization of joint ROM at each segment during the impact phase of the landing.11 Landing softly allows deceleration to occur more slowly, thereby preventing structures from being subjected to the higher forces associated with rapid deceleration.31 The ankle joint ROM, in addition to being the first major joint loaded in the distal-to-proximal sequence, has been identified as a large component in reducing impact forces during landing.11,20 Restriction of sagittal plane ankle joint ROM by several ankle stabilizers has been previously demonstrated during drop landings,28 lateral cutting maneuvers,35 and isolated passive ROM testing.15,29 As stated earlier, the results of McCaw and Cerullo28 prompted the speculation that some ankle stabilizers limit ankle motion and thereby disrupt the contribution of the ankle joint to impact absorption. Two of the stabilizer conditions in their investigation were either precisely identical (ankle tape) or very close (AirCast Sport Stirrup) to those used in the current investigation, and therefore provide assistance in interpreting the present findings. In the present investigation, both the first and second peak impact forces were reached in significantly less time under the ankle tape and brace conditions compared to the control condition. It is speculated that the reduction in time to reach first peak impact force could be related to the ankle tape and brace conditions impeding forefoot and midfoot mobility. Investigations focusing on gait have demonstrated that the foot does not function as one rigid segment, but rather as multiple segments.10 Often, the foot is divided into 3 parts, rearfoot, midfoot, and forefoot. A distinct possibility is that the ankle tape and brace diminished the amount of affordable motion within and between the forefoot and midfoot segments, thereby causing the first peak impact force to be reached sooner. In other words, ankle tape and brace may transform the foot segment into a more

RESEARCH

found with regard to exercise. First, the exercise bout consisted of a controlled straight-ahead jog at moderate intensity. The results of the investigation may have been different if a more functional exercise bout, which included lateral cutting and changeof-direction maneuvers, had been utilized. The current exercise protocol was chosen to minimize the introduction of extraneous variables, such as participant fatigue and task familiarity. By using a treadmill and keeping the speed and time parameters constant across each testing session, the amount of stress imposed onto the ankle joint, ankle tape, and brace could be standardized. Additionally, treadmill jogging is a common activity among many physically active individuals, therefore, the confounding factors associated with multiple exposures to a novel task could be avoided. A second factor potentially explaining the lack of significance was the duration of the exercise bout. A 20-minute session was chosen as a compromise between inducing stress on each ankle appliance while avoiding participant fatigue. With respect to many sport activities, such as soccer and basketball, a 20minute exercise bout may not be representative of the exercise exposure. Future research should focus on incorporating a more functional exercise bout that includes maneuvers requiring various speeds and directions of movement, and exercise bouts of increased duration. The task of landing from the wood platform required subjects to reduce their momentum to 0 without injury. By using a drop landing approach, horizontal velocity was minimized and vertical velocity remained constant across the stabilizer and exercise conditions.11 Therefore, momentum at ground contact can be assumed to be equal across each of the experimental conditions. Reducing momentum to 0 is considered to be the result of an impulse, the product of the average force magnitude, and the length of time the force is applied. Soft and stiff landing strategies were used because of the previously documented energy absorption patterns of the ankle, knee, and hip. As landing stiffness was increased, the ankle joint contributed more to the total energy absorption by the lower limb.11 Therefore, incorporating both strategies into the current investigation permitted study of the effects of ankle stabilizers on vGRFs during tasks in which the ankle had varying roles over total impact energy absorption. The correlational ratios indicating the percentage of total variance attributable to trial for each of the dependent variables provided a method to identify the existence of either linear or nonlinear systematic trends in performance across the multiple trials under each landing style, stabilizer, and time condition.16 Low percentages were revealed, supporting the notion that the participants were proficient and stable in their performance across the 6 trials.

rigid link, by diminishing the amount of movement between the functional units of the foot. The reduction in plantar flexion at floor contact previously revealed under ankle tape and brace conditions28 may potentially explain the quicker time to second peak impact force revealed by the current investigation. Landing with less plantar flexion would result in a floor contact pattern similar to a foot-flat landing strategy. Coupled with a reduction in dorsiflexion, the second peak impact force would seemingly be reached in a shorter time interval. A similar reduction in time to second peak impact force under ankle taping conditions has been previously demonstrated.8 As mentioned previously, decreased force application time should naturally be associated with higher impact forces, however, in the current study, no significant alterations were revealed in peak impact force magnitudes. In addition, to these results opposing the concept of impulse (temporal change without force magnitude change), they are also in contrast to a similar report examining the effects of ankle taping and the combination of ankle and spat taping on vGRF during drop landings from 2 different heights.8 In the previous investigation, significantly higher first (soft landings) and second (soft landings and stiff landings) peak-impact forces collapsed across the 2 landing heights were revealed under ankle tape and tape-and-spat conditions in comparison to a control condition. An important factor to recognize is that the braces used in the investigation were donated by AirCast, Inc., Summit, NJ, and therefore, new at the onset of the study. One could speculate that the materials comprising the brace may deteriorate with repetitive use over time, thereby permitting more ankle motion. It is unknown how much motion is necessary for temporal loading patterns to resemble the control condition. Obviously, one may be concerned that slight increases in ankle ROM, because of material breakdown, may compromise the inversion stabilization purpose of the appliance. Because in clinical practice new braces are often administered at the beginning of a season, future research should investigate what effects repetitive stress on braces during athletic participation may have on vGRF during drop landings. A second important factor related to the investigation was that participants wore standardized laboratory shoes during the landings. This approach was used to reduce the possibility of promoting confounding variability as a result of different shoes interacting with the 2 ankle stabilizers. While this decision increased the internal validity of the study, the possibility exists that the laboratory shoes could have been uncomfortable or unfamiliarity with the shoes may have influenced participants’ performance. 634

The clinical importance of this investigation is the question that emerges concerning the abundant use of ankle taping and bracing as prophylactic procedures against inversion ankle sprains. The results of the present investigation, as well as the previous investigations focusing on drop landings,8,28 suggest that prophylactic ankle taping and bracing may not be benign clinical procedures void of adverse effects or risk. Specifically, the data appear to indicate that ankle taping and bracing may adversely influence impact absorption during drop landings, which based on the speculation by McCaw and Cerullo,8,28 may reflect increased energy dissipation demands at the knee and hip. However, before one speculates upon the clinical implications of this hypothesis, one must remember that this investigation, as well as the previous studies,8 used vGRFs to study the impact period following landing. Because vGRF reflects acceleration of the body’s center of mass, further study incorporating ankle, knee, and hip joint kinematics and kinetics is needed to precisely determine the source of the vGRF alterations. Lastly, while one could argue that the drop landing heights used in these investigations represent extreme circumstances, one should also accept the proposition that similar, subtler, effects may occur with all dynamic activity involving lower landing heights.

CONCLUSIONS Based on the vGRF results of the current investigation, it appears that ankle taping and bracing cause a decrease in the time to reach the peak impact forces. These alterations suggest that during dynamic activity, the musculoskeletal structures of the body are subjected to peak loads within shorter time periods. The clinical importance of the slight temporal differences revealed under the stabilizer conditions, and whether these effects are detrimental over time, remains speculative at this point and requires further research.

REFERENCES 1. Alves JW, Alday RV, Ketcham DL, Lentell GL. A comparison of the passive support provided by various ankle braces. J Orthop Sports Phys Ther. 1992;15:10– 18. 2. Anderson DL, Sanderson DJ, Hennig EM. The role of external nonrigid ankle bracing in limiting ankle inversion. Clin J Sport Med. 1995;5:18-24. 3. Arnheim DD, Prentice WE. Principles of Athletic Training. St. Louis, MO: Mosby Year Book; 1993. 4. Bahr R, Karlsen R, Lian O, Ovrebo R. Incidence and mechanisms of acute ankle inversion injuries in volleyball: a retrospective cohort study. Am J Sports Med. 1994;22:595–600.



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RESEARCH

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