Effect of a 4-Week Agility-Training Program on Postural Sway in the Functionally Unstable Ankle

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1 Effect of a 4-Week Agility-Training Program on Postural Sway in the Functionally Unstable Ankle Damien M. Hess, Christopher J. Joyce, Brent L. Arnold, and Bruce M. Gansneder Context: Agility training has been proposed as an important tool in rehabilitation. However, it is unclear which types of agility training are most useful. Objective: To assess the effects of agility training on balance in individuals with functionally unstable ankles. Design: A 2-group experimental design with repeated measures. Setting: Laboratory. Patients: Twenty college-aged volunteers, each with 1 functionally unstable ankle, were randomly assigned to 1 of 2 groups. Interventions: Subjects in the experimental group performed agility training 3 times per week for 4 weeks. Main Outcome Measures: Subjects were tested for static single-leg balance before and after the training period. Anterior/posterior sway amplitude, medial/lateral sway amplitude, and sway index were assessed using the Chattex Balance System. Results: No significant differences in balance were found after the agility training. Conclusions: Agility training did not improve static single-leg balance in subjects with functionally unstable ankles. Key Words: proprioception, exercise, balance, ankle sprain Hess DM, Joyce CJ, Arnold BL, Gansneder BM. Effect of a 4-week agility-training program on postural sway in the functionally unstable ankle. J Sport Rehabil. 2001;10: Human Kinetics Publishers, Inc. Functional instability was initially defined in 1965 as a feeling of giving way after an ankle sprain, which suggested that a motor incoordination resulted from partial articular deafferentiation. 1 Many authors have since used this definition to identify subjects and study aspects of functionally unstable ankles, including causes of the instability 2-8 and methods of preventing it Hess is with the US Olympic Committee, Lake Placid, NY Joyce is with the Department of Health Sciences at the University of North Florida, Jacksonville, FL Arnold and Gansneder are with the Department of Human Services at the University of Virginia, Charlottesville, VA

2 Agility Training, Postural Sway, and the Ankle 25 Three factors have been identified as possible causes of functional instability of the ankle joint: mechanical instability, 2,3,18 muscular function, 3-6,18 and proprioceptive deficits. 1-4,6,18 Anatomic laxity is not considered a primary cause, 2,3,18 although it might perpetuate the condition once an injury has occurred. 3 One study demonstrated that only 32% of subjects who complained of functional instability had an anatomical laxity and that 59% had no difference between involved and uninvolved ankles. 3 Decreases in muscle function such as peroneal weakness 3,5,18 and prolonged peroneal reaction time 4,6 have been considered potential causes, though usually secondary to proprioceptive deficits. Some studies demonstrated no significant peroneal weakness in functionally unstable as compared with contralateral limbs. 3,5,18 Those that have examined prolonged peroneal reaction times have suggested a diminished afferent response during the reflexive muscular activity responsible for stabilization of the ankle joint. 4 However, in healthy individuals peroneal reaction times are too slow to prevent inversion injury at the time of heel strike, suggesting that greater delays in peroneal reaction time after injury are an unlikely cause of functional instability. 8 Deficits in proprioception have been measured in various studies, and the results are somewhat conflicting depending on the type of measurement used. 1-3,5,9-14,18 Studies that used subjective measures, such as a modified Romberg test or detection of passive motion, found differences between functionally unstable and stable limbs. 1,3,5 Studies that used more objective measures such as postural sway or stabilometry revealed no significant differences in the same measures between limbs, 10,18 but others did find differences between the functionally unstable subjects and control subjects. 2,11 In order to minimize proprioceptive deficits, rehabilitative training has been implemented after ankle injuries. 9-11,17 The 2 types of training primarily used are strength training 15,17,19-25 and balance/coordination training. 9-12,14,16,17,25 Strength-training programs have produced increases in active joint-reposition sense. 15 Ankle-disk training for balance/coordination has provided improvements in postural sway. 9-11,14 Although those types of training have been shown to improve joint-reposition sense and postural sway in the ankle, they do not mimic functional activities for sports. Agility-training programs can be designed to simulate sport-specific activities. One study focusing on the knee demonstrated an improvement in voluntary response times of the gastrocnemius, hamstring, and quadriceps muscle groups through agility training, whereas isokinetic and isotonic strength-training programs did not. 25 Thus, we were interested in determining whether agility training might provide a more ef-fective method of reducing functional instability. The purpose of this study was to examine the effect of a 4-week agility-training program on the proprioception of the functionally unstable ankle via a single-leg postural-sway measure.

3 26 Hess et al Subjects Methods Twenty volunteers (13 women, 7 men: age = 20.9 ± 3.02 years, height = ± 9.15 cm, weight = 74.2 ± kg) participated in this study. The criterion for participation was a functionally unstable ankle, defined as a history of 1 or more lateral ankle sprains that required medical treatment and that presented with a feeling of giving way during daily or sport activities. 1 Only 1 researcher determined the presence of a functional instability and selected participants. In addition, the involved ankle was not acutely injured at the time of the study, and subjects did not have any uncorrected visual or vestibular deficits. All subjects read and signed an informed consent agreement prior to participation. A university institutional review board for the behavioral sciences approved all testing and training procedures. Instrumentation The Chattex Balance System (CBS; Chattanooga Group, Inc, Hixson, Tenn), which measures subjects postural sway in the anterior/posterior (A/P) and medial/lateral (M/L) directions, was used for all balance tests (Figure 1). Raw analog sway data are collected at 1000 Hz from 4 load cells under the subject s foot. These data are digitally converted by the CBS and sent to a PC for postural-sway calculations. Postural sway (A/P and M/L) is calculated from the raw data as the root mean square of the distance in centimeters away from the center of balance. The overall sway index is a bivariate root mean square similar in form to a covariance. The center of balance is defined by the CBS as the point at which the center of pressure is located when an individual s weight is applied equally on the system s 4 load cells. Testing Procedures Only the functionally unstable ankle was used for balance testing in this study. All subjects were pretested for single-leg static balance with eyes open and were barefoot to minimize effects from footwear. Each subject was positioned on the CBS in a manner consistent with the operating manual. Subjects were then informed about the sequence of events for the testing procedures. Two 20-second practice trials were followed by a 2-minute rest period before the actual testing procedure. The balance test consisted of three 20-second trials in a single-leg stance with a 1-minute rest between trials. The opposite limb was held with the hip and knee flexed in a position of comfort for each subject but was not allowed to touch the support leg during balance testing. The arms were held along the sides of the body. If

4 Agility Training, Postural Sway, and the Ankle 27 Figure 1 Subject positioning on Chattex Balance System for balance testing. subjects lost their balance they were permitted to touch the handrail of the CBS with the dorsal aspect of the hand to regain balance, but they were instructed to regain balance as soon as possible and place their hands at their sides again. The results of the 3 trials were averaged together to obtain a mean measurement for the A/P- and M/L-sway amplitudes, as well as a sway-index value. At the conclusion of the training period, all subjects were posttested in the same manner. Training Procedures Subjects were randomly assigned to a control group or an experimental group. Once all the subjects were pretested, the experimental group participated in 4 weeks of agility training using the ABC Agility Ladder (M-F Athletic Co, Cranston, RI). The ABC Agility Ladder was chosen because it is used for agility training in many sports. We are unaware of any research

5 28 Hess et al that supports the specific exercise program we used, but we did use exercises recommended by the manufacturer. Thus, the purpose of this study was to determine whether the agility training would have an effect, especially with functionally unstable ankles. Subjects performed agility training 3 times a week for 4 weeks, and each training session lasted approximately 20 minutes. The sessions began with a 3- to 5-minute warm-up consisting of slow movements on the ladder in a manner similar to the training drills. Subjects were then encouraged to properly stretch the lower extremities to their tolerance and comfort. After the warm-up, each subject completed a series of 7 drills designed to improve agility. The series of drills took approximately minutes to complete. Each drill was repeated 2 times, and 1 repetition consisted of performing the drill along the entire length of the ladder. There was a 15-second rest period between repetitions and between drills. The series of drills used in this study was selected from the manufacturer s manual and was as follows: 1. Forward 2-Feet-In: Subjects stood facing down the length of the ladder. They moved forward through the ladder, touching both feet in each space. One drill was done with the left foot leading and the other with the right foot leading. 2. Lateral 2-Feet-In: Subjects stood sideways with 1 shoulder facing down the length of the ladder. They moved laterally through the ladder, touching both feet in each space. One drill was done with the left foot leading and the other with the right foot leading. 3. Forward Shuffle: Subjects stood along the left side of the ladder facing down its length. They stepped into the first space with the right foot, then the left foot, then out on the right side with the right foot. The left foot then landed first in the second space, followed by the right foot, and out on the left side with the left foot. 4. One-Foot-In Ali Shuffle: Subjects stood on 1 side of the ladder with 1 shoulder facing down its length. They began with the lead foot in the first space and the trail foot behind the lead foot, but outside the first space. They jumped and switched foot positions so that the trail foot landed in the second space. They jumped again and landed so that the lead foot was in the third space. One drill was done with the left foot leading and the other with the right foot leading. 5. Forward Slalom Jumps: Subjects stood facing down the length of the ladder. They placed 1 foot inside the first space with the other foot parallel, but outside of the first space. They jumped and landed with the outside foot in the second space and the inside foot parallel to, but outside of, the second space. They jumped again and landed so that the feet were in a position similar to the start of the drill and continued down the ladder. 6. Forward Cross-Steps: Subjects stood on the left side of the ladder facing down its length. They crossed the left foot over the right foot and

6 Agility Training, Postural Sway, and the Ankle 29 touched it into the first space. The right foot then landed on the right side of the ladder next to the second space, followed by the left foot. Once the left foot landed, they crossed the right foot over the left and touched it into the second space. The left foot then landed on the left side of the ladder next to the third space, followed by the right foot Angle: This was a combination of drills 1 and 2, but with a 90 turn at the middle of the ladder. Subjects moved forward through the ladder using the Forward 2-Feet-In drill. At the turn, they planted on the outside foot and continued along the ladder using the Lateral 2-Feet-In drill. This drill was done once with a 90 left turn and once with a 90 right turn. Subjects in the control group were instructed to continue with their normal daily activities for the duration of the training period. All subjects in the study were instructed to not initiate any new training programs or activities that could affect the results of this study. Statistical Analysis A multivariate analysis of variance (MANOVA) was performed for A/Pand M/L-sway measures. Because the sway index is a composite measure of the A/P and M/L indexes, it was treated separately to reduce autocorrelations. Significant multivariate tests were followed by univariate tests. For each dependent measure, univariate tests consisted of separate Test Group Gender analyses of variance (ANOVAs) with repeated measures for the test factor. All statistical analyses were performed using SPSS version 9.0 for Windows (SPSS, Inc, Chicago, Ill). If interactions were significant, mean comparisons were tested with the Tukey post hoc procedure. The alpha level was set at P.05 a priori for all statistical tests. Results The means for A/P and M/L sway are presented in Tables 1 and 2, respectively. The MANOVA for A/P and M/L sway produced no significant Table 1 Mean ± SD Anterior/Posterior-Sway-Amplitude Values (cm) Men Women Group Pretest Posttest Pretest Posttest Control 5.89 ± ± ± ± 0.91 Experimental 3.50 ± ± ± ± 0.40

7 30 Hess et al Table 2 Mean ± SD Medial/Lateral-Sway-Amplitude Values (cm) Men Women Group Pretest Posttest Pretest Posttest Control 2.42 ± ± ± ± 0.37 Experimental 1.80 ± ± ± ± 0.26 Table 3 Mean ± SD Sway-Index Values Men Women Group Pretest Posttest Pretest Posttest Control 1.29 ± ± ± ± 0.19 Experimental 0.69 ± ± ± ± 0.10 Table 4 (cm) Mean ± SD Sway-Index Values for the Gender Group Interaction Group Men Women Mean Control 1.27 ± 0.11* 0.77 ± ± 0.07 Experimental 0.75 ± ± ± 0.08 Mean 1.01 ± ± 0.06 *Significantly different than male experimental and female control. Significantly different than experimental. Wilks lambdas. The group factor had the smallest Wilks lambda ( =.681, P =.06). The ANOVA for sway-index values produced no significant differences between pretest and posttest measures for sway index (Table 3). Furthermore, a significant main effect for group (F 1,16 = 4.663, P =.046) and a significant Gender Group interaction (F 1,16 = 8.193, P =.011) were the only significant differences found (Table 4). Post hoc analysis revealed that the male control subjects had a significantly greater sway-index value than did the male experimental and female control subjects.

8 Agility Training, Postural Sway, and the Ankle 31 Comments Our agility-training program did not affect postural sway in individuals with functionally unstable ankles. We have postulated a few potential reasons that no differences were found, including the choice of dependent measure, changes in the postural-control strategies used, and adaptations to the training. The use of static single-leg balance might not have been the appropriate dependent measure to examine the effects of agility training. There are 3 components of postural control that could account for a functional instability: visual input, vestibular input, and somatosensory input. 7,26-31 Dietz et al 27 concluded that the vestibular system was more involved with slow body sway, but somatosensory input was important in controlling the body s balance during shifts in center of gravity. The agility training used in this study produced large shifts in center of gravity, but the balance tests were done in a static manner. Thus, a dynamic test might have been more appropriate, as well as techniques that would have measured the frequency of sway rather than sway amplitude. There are 2 strategies of postural control, the ankle strategy and the hip strategy. 32,33 The ankle strategy is so named because the forces used to move the center of body mass occur at the ankle, and it is used in response to small, slow horizontal displacements on surfaces larger than the feet. 33 The hip strategy, on the other hand, is used in response to larger, faster displacements or on surfaces that are smaller than the feet, and it moves the center of body mass through forces at the hip. 33 Healthy individuals use a combination of the 2 strategies to maintain balance, 32,33 but injured subjects have been shown to use altered postural-control strategies. 28,29,32 Specifically, Horak et al 28 found that subjects with a somatosensory loss used an increased hip strategy but had an absence of hip strategy with a vestibular loss. Although hip strategy was not measured in our study, casual observation suggested its use in balance control. Thus, we believe a more detailed analysis of postural-control strategies might be warranted. Studies have demonstrated an increase in neural activity during the first 3 5 weeks of strength training in various populations. 19,21-24 Strength training also improved joint-position sense in subjects with functionally unstable ankles. 15 The results of the current study suggest that the same effects might not occur from agility training. Balance/coordination studies have shown improvements in static singleleg balance measures when the training methods were very similar to the testing measures. 9-11,16,17 The agility training in this study was a dynamic activity, and the balance testing was static in nature, which could explain why significant improvements in postural sway were not observed. Electromyography might have been a more appropriate measure to use with agility training. Konradsen and Ravn 4 postulated that delayed peroneal

9 32 Hess et al reaction times were the result of a proprioceptive deficit, which supported the theory proposed by Freeman et al. 1 Some authors have suggested that central motor-program changes are responsible for restoring posturalcontrol strategies to normal. 10,11 Electromyography might demonstrate an improvement in the muscle timing, which could lead to a decrease in symptoms of functional instability. Another device that might have provided more useful results is the Biodex Stability System (BSS; Biodex, Inc, Shirley, NY). As described by Arnold and Schmitz, 34 the BSS assesses balance via an unstable platform and measures deviations from horizontal rather than postural sway. They demonstrated that the A/P component is very closely related to and accounts for 95% of the overall postural sway. 34 Their results also demonstrated that the patterns of A/P, M/L, and overall postural sway are similar to the measures obtained from other objective devices such as the CBS. 34 In addition, recent evidence suggests that the BSS is effective in detecting differences between normal and functionally unstable ankles and that it can detect improvements in joint stability after balance training. 35 The results of our study also indicate that there were no significant improvements in postural sway for either gender or group. Despite the fact that we used random assignment to the control and experimental groups, there were significant differences between the 2 groups. The men in the control group were significantly different from any other group in the study (see Table 4), which should have only occurred by chance. They were slightly taller and older than any other group, but not by any appreciable amount. The number of subjects used in this study was limited because we were unable to identify enough volunteers who fit the inclusion criteria; this decreased the power of the study. We were not interested in using athletes, because they train on a regular basis. Most athletes who have sustained ankle injuries might have done some type of agility training as part of their rehabilitation, which could have made it more difficult to demonstrate improvements in postural sway in that population. Also of interest was the fact that there were more women than men in our study. Conclusion The results of this study revealed no significant differences in static single-leg balance measures between pretest and posttest in subjects with functionally unstable ankles. Our conclusion is that agility training does not objectively improve static single-leg balance measures after 4 weeks of training. Anecdotally, subjects who performed 4 weeks of agility training reported that they felt more stable and were better able to perform after training, and we also observed improvement in the agility-drill performance as the training sessions progressed. We would recommend this model to

10 Agility Training, Postural Sway, and the Ankle 33 be used as a basis for future research, but with a larger sample size. We would also recommend examining the effects of agility training on different dependent measures such as dynamic balance testing and electromyography. Acknowledgments We would like to thank the University of Virginia Sports Medicine Department for the use of their agility ladder in this study. This study was conducted as part of a master s thesis by the lead author at the University of Virginia. References 1. Freeman MAR, Dean MRE, Hanham IWF. The etiology and prevention of functional instability of the foot. J Bone Joint Surg Br. 1965;47: Tropp H, Odenrick P, Gillquist J. Stabilometry recordings in functional and mechanical instability of the ankle joint. Int J Sports Med. 1985;6: Lentell G, Baas B, Lopez D, McGuire L, Sarrels M, Snyder P. The contributions of proprioceptive deficits, muscle function, and anatomic laxity to functional instability of the ankle. J Orthop Sports Phys Ther. 1995;21: Konradsen L, Ravn JB. Ankle instability caused by prolonged peroneal reaction time. Acta Orthop Scand. 1990;61: Lentell GL, Katzman LL, Walters MR. The relationship between muscle function and ankle stability. J Orthop Sports Phys Ther. 1990;11: Löfvenberg R, Kärrholm J, Sundelin G, Ahlgren O. Prolonged reaction time in patients with chronic lateral instability of the ankle. Am J Sports Med. 1995;23: Hertel JN, Guskiewicz KM, Kahler DM, Perrin DH. Effect of lateral ankle joint anesthesia on center of balance, postural sway, and joint position sense. J Sport Rehabil. 1996;5: Konradsen L, Voigt M, Højsgaard C. Ankle inversion injuries: the role of the dynamic defense mechanism. Am J Sports Med. 1997;25: Bernier JN, Perrin DH. Effect of coordination training on proprioception of the functionally unstable ankle. J Orthop Sports Phys Ther. 1998;27: Tropp H, Ekstrand J, Gillquist J. Factors affecting stabilometry recordings of single limb stance. Am J Sports Med. 1984;12: Gauffin H, Tropp H, Odenrick P. Effect of ankle disk training on postural control in patients with functional instability of the ankle joint. Int J Sports Med. 1988;9: Cox ED, Lephart SM, Irrgang JJ. Unilateral balance training of noninjured individuals and the effects on postural sway. J Sport Rehabil. 1993;2: Lundin TM, Feuerbach JW, Grabiner MD. Effect of plantar flexor and dorsiflexor fatigue on unilateral postural control. J Appl Biomech. 1993;9:

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12 Agility Training, Postural Sway, and the Ankle Isakov E, Mizrahi J. Is balance impaired by recurrent sprained ankle? Br J Sports Med. 1997;31: Brunt D, Andersen JC, Huntsman B, Reinhert LB, Thorell AC, Sterling JC. Postural responses to lateral perturbation in healthy subjects and ankle sprain patients. Med Sci Sports Exerc. 1992;24: Horak FB, Nashner LM. Central programming of postural movements: adaptation to altered support surface configurations. J Neurophysiol. 1986;30: Arnold BL, Schmitz RJ. Examination of balance measures produced by the Biodex Stability System. J Athletic Train. 1998;33: Rozzi SL, Lephart SM, Sterner R, Kuligowski L. Balance training for persons with functionally unstable ankles. J Orthop Sports Phys Ther. 1999;29: