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Balance Training Improves Function and Postural Control in Those with Chronic Ankle Instability

Balance Training Improves Function and Postural Control in Those with Chronic Ankle Instability
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  Copyright @ 200 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. 8 Balance Training Improves Functionand Postural Control in Those with Chronic Ankle Instability  PATRICK O. MCKEON 1 , CHRISTOPHER D. INGERSOLL 2 , D. CASEY KERRIGAN 2 , ETHAN SALIBA 2 ,BRADFORD C. BENNETT 2 , and JAY HERTEL 2 1 University of Kentucky, Lexington, KY; and   2 University of Virginia, Charlottesville, VA ABSTRACT MCKEON, P. O., C. D. INGERSOLL, D. C. KERRIGAN, E. SALIBA, B. C. BENNETT, and J. HERTEL. Balance Training ImprovesFunction and Postural Control in Those with Chronic Ankle Instability.  Med. Sci. Sports Exerc. , Vol. 40, No. 10, pp. 1810–1819, 2008. Purpose:  The purpose of this randomized controlled trial was to determine the effect of a 4-wk balance training program on static anddynamic postural control and self-reported functional outcomes in those with chronic ankle instability (CAI).  Methods:  Thirty-oneyoung adults with self-reported CAI were randomly assigned to an intervention group (six males and 10 females) or a control group(six males and nine females). The intervention consisted of a 4-wk supervised balance training program that emphasized dynamicstabilization in single-limb stance. Main outcome measures included the following: self-reported disability on the Foot and AnkleDisability Index (FADI) and the FADI Sport scales; summary center of pressure (COP) excursion measures including area of a 95%confidence ellipse, velocity, range, and SD; time-to-boundary (TTB) measures of postural control in single-limb stance including theabsolute minimum TTB, mean of TTB minima, and SD of TTB minima in the anteroposterior and mediolateral directions with eyesopen and closed; and reach distance in the anterior, posteromedial, and posterolateral directions of the Star Excursion Balance Test (SEBT).  Results:  The balance training group had significant improvements in the FADI and the FADI Sport scores, in the magnitudeand the variability of TTB measures with eyes closed, and in reach distances with the posteromedial and the posterolateral directions of the SEBT. Only one of the summary COP-based measures significantly changed after balance training.  Conclusions:  Four weeks of  balance training significantly improved self-reported function, static postural control as detected by TTB measures, and dynamic posturalcontrol as assessed with the SEBT. TTB measures were more sensitive at detecting improvements in static postural control comparedwith summary COP-based measures.  Key Words:  ANKLE SPRAIN, DYNAMIC BALANCE, FUNCTIONAL OUTCOMES,REHABILITATION, TIME-TO-BOUNDARY A nkle sprains are among the most common injuriesin the physically active population (4). The most common predisposing factor to experiencing anankle sprain is a previous history of ankle sprain (1). Thesubjective feeling of the ankle ‘‘giving way’’ after an initialankle sprain and repetitive bouts of instability resulting innumerous ankle sprains has been termed chronic ankleinstability (CAI) (16). CAI has been linked to manydifferent contributing factors, including deficits in posturalcontrol (2,12,17,21,26,27).Balance training has been purported to be an effectivemodality in the rehabilitation and prevention of recurrent sprains in those with CAI; however, there is limitedevidence of its effectiveness (3,9,26,28). For example, Eilsand Rosenbaum (9) reported a 60% decrease in self-reported episodes of the ankle ‘‘giving way’’ into inversionin individuals with CAI 1 yr after undergoing 6 wk of  balance and coordination training, but they did not report values for a control group for comparison. Traditionally, balance training has involved single-limb stance activitieson stable and unstable surfaces (9,28). Although self-reported improvements in functional status have beendemonstrated in response to balance training (9,26), there isconflicting evidence that postural control improvementsoccur as a result of balance training in individuals withCAI (3,9,26). The traditional measures used to assess theimprovements in postural control may have lacked thesensitivity to detect improvements (21). Moreover, these balance training programs may have not appropriatelychallenged the sensorimotor system to elicit a detectablechange in postural control. A balance training program that emphasizes the dynamic stabilization after perturbations suchas predictable and unpredictable changes in direction, landing Address for correspondence: Patrick O. McKeon, Ph.D., ATC, CSCS,Division of Athletic Training, College of Health Sciences, University of Kentucky, Wethington Building, Room 206C, 900 S Limestone, Lexing-ton, KY 40536-0200; Email: for publication September 2007.Accepted for publication April 2008.0195-9131/08/4010-1810/0MEDICINE & SCIENCE IN SPORTS & EXERCISE  Copyright     2008 by the American College of Sports MedicineDOI: 10.1249/MSS.0b013e31817e0f92 1810       A      P      P      L      I      E      D      S      C      I      E      N      C      E      S  Copyright @ 200 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. 8 from a hop, and dynamic reaching tasks may prove more beneficial than the traditional balance training programs.Several investigators (2,26,27) have demonstrated that individuals experiencing CAI have a decreased ability toeffectively maintain single-limb stance. This has tradition-ally been assessed using a variation of the Romberg test ona force plate. Traditional force plate measures of posturalcontrol such as average center of pressure (COP) excursionvelocity and COP excursion area have not consistentlydetected postural control deficits associated with CAI (22)and have not detected significant improvements associatedwith rehabilitation in this population (23). A novel approachto assessing postural control differences in single-limbstance related to CAI is time-to-boundary (TTB) analysis(20,21). TTB is a spatiotemporal analysis of COP data  points. It quantifies the theoretical amount of time anindividual has to make a postural correction to maintain postural stability. In a comparison of females with CAI andhealthy female controls, Hertel and Olmsted-Kramer (21)demonstrated that the magnitude and the variability of TTBmeasures in single-limb stance were lower in the CAIgroup. The CAI group had significantly less time to make postural corrections and did so in a less variable manner than healthy controls. It was hypothesized that thisreduction in magnitude of TTB measures was related to a diminished ability to respond effectively to changes in postural control demands (21). In those with CAI, thereduction in the variability of the TTB measures may beindicative of a more constrained sensorimotor system(13,29). Traditional COP-based measures of COP excursionvelocity, range, and SD failed to detect these posturalcontrol alterations (21). Currently, there is no evidence tosuggest that these TTB deficits can be improved throughrehabilitation. Perhaps TTB measures may provide greater insight into postural control alterations associated with balance training in those with CAI where traditional COP- based measures have not.The effects of CAI on dynamic postural control have also been examined. The Star Excursion Balance Test (SEBT) isan assessment of dynamic postural control consisting of a series of lower-extremity reaching tasks in different direc-tions (17). Significant deficits in dynamic postural control inindividuals with CAI have been detected with the use of theSEBT (11). Individuals with CAI demonstrated a signifi-cantly decreased ability to reach while standing on theinjured limb compared with their uninjured limbs andmatched controls (24). The anterior (A), the posteromedial(PM), and the posterolateral (PL) directions have been shownto be the most effective in assessing dynamic balance inthose with CAI (17). Currently, there is limited evidence tosuggest that deficits in SEBT reach distance associated withCAI can be corrected through rehabilitation (15).To date, there have been no randomized controlled trialsthat have examined the effects of supervised dynamic balance training on static and dynamic postural control aswell as self-reported functional outcomes in those with CAI.Therefore, the purpose of this study was to determine theeffect of a 4-wk supervised balance training program onstatic and dynamic postural control and self-reported func-tional outcomes in those with CAI. We hypothesized that individuals with CAI who underwent dynamic balancetraining would have significant improvements in self-reported functional status, static postural control as assessed by TTB measures and traditional COP-based measures, anddynamic postural control as assessed with the SEBT. METHODS Study design.  This study was a randomized controlledtrial in which individuals with self-reported CAI wererandomly assigned to one of two groups: a balance traininggroup or a control group. The balance training groupunderwent 12 supervised balance training sessions duringa 4-wk period. The control group maintained the same levelof activity before study enrollment for the duration of 4 wk.Measures of self-reported function and static and dynamic postural control were taken before and after the 4-wk intervention in both the balance training and the controlgroups. Subjects.  Thirty-one physically active individuals witha self-reported history of CAI were recruited to participatein the study. Inclusion criteria were a history of more thanone ankle sprain and residual symptoms, includingsubsequent episodes of the ankle giving way as quantified by four or more ‘‘yes’’ responses on the Ankle InstabilityInstrument (8). Also included were self-reported symptomsof disability due to ankle sprains qualified by a score of 90% or less on the Foot and Ankle Disability Index (FADI)and the FADI Sport surveys. These instruments havedemonstrated high intersession reliability and have beenshown to be valid in detecting differences related to CAIand improvements after rehabilitation in those with CAI(14). The FADI contains 26 items related to activities of daily living, and the FADI Sport contains eight items that evaluate perceived disability due to foot or ankle injuryin activities associated with physical activity and sport  participation (14). All subjects had no history of lower-extremity injury, including ankle sprain, within the past 6wk, no history of lower-extremity surgery, and no balancedisorders, neuropathies, diabetes, or other conditions knownto affect balance. If a subject reported bilateral ankleinstability, the self-reported worse limb was used for analysis and training. Before testing, all subjects signedan informed consent form approved by the universityinstitutional review board.Once informed consent was obtained, subjects wererandomly assigned to either a balance training group or a control group. The randomization was concealed and prepared by an independent investigator. The balancetraining group consisted of six males and 10 females((mean  T SD) age = 22.2  T  4.5 yr; height = 168.9  T 7.7 cm; mass = 63.0  T  8.8 kg) and reported 6.3  T  7.1 BALANCE TRAINING AND ANKLE INSTABILITY Medicine & Science in Sports & Exercise d  1811 A P  P  L  I    E   D  S   C I    E  N  C E   S    Copyright @ 200 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. 8  previous sprains with 10.7  T  7.0 months since the last significant sprain. They reported a mean  T  SD score of 85.5  T  8.4% on the FADI and 69.9+12% on the FADISport. The control group consisted of six males and ninefemales (mean  T  SD age = 19.5  T  1.2 yr; height = 173.1 cm;mass = 67.3 kg) and reported 4.6  T  2.5 previous significant ankle sprains with 5.5  T  3.9 months since the last significant sprain. The mean  T  SD FADI and the FADI Sport scoreswere 82.9  T  7.4% and 66.4  T  9.8%, respectively. INSTRUMENTATION Static postural control was assessed with the AccuswayPlus force plate (AMTI; Watertown, MA). Force andmoment signals were filtered with a fourth-order, zero lag,low-pass filter with a cutoff frequency of 5 Hz. COP data were calculated from the three-dimensional force andmoment signals and sampled at a rate of 50 Hz (20). PROCEDURES Static postural control.  Subjects performed threetrials of single-limb stance on each leg with eyes openand closed on a force plate (Accusway Plus; AMTI) for 10 s(20,21). Subjects were instructed to stand as still as possibleduring testing with arms folded across their chests, holdingthe opposite limb at approximately 45 -  of knee flexion and30 -  of hip flexion in accordance with a previouslyestablished protocol (18,20,21). If a subject touched downwith the opposite limb, made contact with the stance limb,or was unable to maintain standing posture during the 10-strial, the trial was terminated and repeated. Dynamic postural control.  The SEBT hasdemonstrated high intersession reliability and has beenshown to be valid in detecting deficits associated with CAI(12,17,19). Subjects were positioned and aligned with a tape measure secured to the floor in accordance with Hertelet al. (17). Subjects maintained a single-limb stance whilereaching as far as possible along a cloth tape measuresecured to the floor in the relevant line of direction withtheir opposite limb, made a light touch on the line, andreturned to the starting position (12). The reach distances of three trials of the A, the PM, and the PL directions wererecorded for each limb (17). These directions have beenshown to assess unique aspects of dynamic postural control.A trial was discarded and repeated if a subject placedexcessive weight on the reaching limb, removed the stancefoot from the starting position, or lost balance (10). Reachdistance was normalized to the subject’s leg length inaccordance with previously established methods (10). Themean of three trials for each direction was used for analysis. Data reduction.  TTB measures were computed using previously described methods (20). The mean of three trialsfor each measure was used for analysis. To calculate TTB,we modeled each subject’s foot as a rectangle, based onlength and width measurements, to separate the antero- posterior (AP) and mediolateral (ML) components of COP(20). TTB measures estimated the time it would take theCOP to reach the boundary of the base of support if theCOP were to continue on its trajectory without a change invelocity (20). TTB was processed with the use of a customsoftware program in MatLab (MathWorks, Inc, Natick,MA). For each COP data point in the ML direction(COPML), the instantaneous position and velocity wereused to calculate TTB. The distance between COPML i  andthe previous COPML data point was calculated and divided by the sampling rate (0.02 s) to determine the velocity of COPML i . If COPML i  was moving medially, the distancefrom the COPML i  instantaneous position to the respective(medial) boundary of the foot was determined. By dividingthe COPML i  distance to the boundary by its velocity, thetheoretical time it would take COPML i  to reach the medial border of the foot if it continued on the same trajectorywithout a change in velocity or direction was calculated(20). If the COP data point was moving laterally, thedistance of the COP data point to the lateral border of thefoot was determined. TTB in the AP direction (TTBAP)was calculated similarly to TTB in the ML direction(TTBML) using the AP borders of the foot. Each TTBseries in the ML and AP directions produced a data sequence of peaks and valleys. The valleys represented theTTB minima, the lowest values in the TTB series. Thesedata points represent the critical times where thesensorimotor system had the least time to make a posturalcorrection to maintain single-limb stance over the base of support (20). From the identification of TTB minima, theabsolute minimum TTB (the lowest minimum value), themean of the TTB minima (measurement of TTBmagnitude), and the SD of TTB minima (measurement of TTB variability) were computed separately for the ML andthe AP directions. The mean of each measure for the threeeyes-open and eyes-closed trials was used for statisticalanalysis.Traditional COP-based measures of the SD of COPexcursions, range of COP excursions (distance between themaximum and the minimum COP positions), and meanvelocity of COP excursions (total COP excursion length incentimeters divided by the 10-s trial time) in the ML and theAP directions were calculated. The area of the 95%confidence ellipse of COP excursions was also calculated.The mean of each measure for the three eyes-open andeyes-closed trials was used for statistical analysis. BALANCE TRAINING PROGRAM Subjects randomly assigned to the 4-wk progressive balance-training program participated in 12 supervisedtraining sessions, three sessions per week (25,26). Eachsession lasted approximately 20 min. The progressive balance training program (see Appendix) was designed tochallenge a subject’s ability to maintain a single-limb stance 1812  Official Journal of the American College of Sports Medicine       A      P      P      L      I      E      D      S      C      I      E      N      C      E      S  Copyright @ 200 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. 8 while performing various balance activities (3,7). Duringeach session, subjects performed dynamic balance activitiesdesigned to challenge recovery of single-limb balanceefficiently after a perturbation and to effectively developspontaneous strategies to execute movement goals. As a subject developed proficiency within the program, the task and environmental constraints placed on the sensorimotor system were progressively increased. Each activity con-tained seven levels of difficulty through which subjectsadvanced. These novel activities were intended to promotethe restoration of functional variability within the senso-rimotor system. Activities included 1) hop to stabilization,2) hop to stabilization and reach, 3) hop to stabilization boxdrill, 4) progressive single-limb stance balance activitieswith eyes open, and 5) progressive single-limb stanceactivities with eyes closed. Statistical analysis.  The independent variables weregroup (balance training and control) and time (pretest and posttest). Separate 2    2 repeated-measures ANOVA wereused to assess changes in the dependent measures due to balance training. FADI and FADI Sport measures werecompared both between and within groups. Postural controlmeasures were separated into TTB measures and traditionalCOP-based measures and were analyzed independently.Eyes-open trials during static postural control wereanalyzed separately from eyes closed. For SEBT measures,the three reach distances were analyzed separately. Tukey’sHSD was used for   post hoc  pairwise comparisons to explainany significant interactions. Alpha level was set   a priori  at   P   G  0.05. Cohen’s  D  measures of effect size (5) weredetermined by calculating the mean difference betweengroups (balance training and control) or tests (pretest and posttest) and dividing it by the reference SD (pretest or control). The strength of effect sizes was determined as small( e 0.4), moderate (0.41–0.7), and large effects ( Q 0.71) (5). RESULTS Self-Reported Function Means ( T SD) and effect sizes for FADI and FADI Sport measures are listed in Table 1. There was a significant group    time interaction for the FADI (  P   = 0.03) and theFADI Sport (  P   = 0.009) scores.  Post hoc  comparisonsrevealed that that there were no significant differences between the pretest measures for the FADI and the FADISport between groups. The balance training group FADIand FADI Sport measures were significantly greater after  balance training compared with their pretest measures andwere also significantly greater than the control group posttest measures. Static Postural ControlTTB measures.  For the eyes-open trials, there were nosignificant interactions or main effects for any of the TTBmeasures (Table 2).For the eyes-closed TTB measures, there were significant group    time interactions for the absolute minimumTTBML, the mean of TTBML minima, the mean of TTBAP minima, and the SD of TTBAP minima.  Post hoc comparisons revealed that there was a significant increase inthese measures for the balance training group from pretest to posttest. The balance training group also had signifi-cantly higher TTB measures compared with the controlgroup at posttest on the absolute minimum TTBML, themean of TTBAP minima, and the SD of TTBAP minima. TABLE 1. Pretest and posttest scores on the FADI and the FADI Sport for the balance training and control groups. Balance Training Group Control GroupPretest Posttest Pretest Posttest Group Effect Time Effect FADI, % 85.5  T  8.4 93.7  T  7.4*, †  82.9  T  7.4 81.40  T  18.1 0.68 0.98FADI Sport, % 69.9  T  12.1 85.0  T  14.4*, †  66.5  T  9.8 66.3  T  11.8 1.63 1.25There was a significant group    time interaction for both instruments. There was no difference between groups at pretest, but there was a significant difference between posttestmeasures between groups and a significant difference in self-reported function at posttest for the balance training group,  P   G  0.05. Group effect sizes were calculated from posttestscores. Time effect sizes were calculated from the pretest and posttest measures of the balance training group.*  P   G  0.05 for pretest to posttest comparisons within the balance training group. † P   G  0.05 for between-groups comparisons at posttest.TABLE 2. Pretest and posttest TTB in the ML and AP directions with eyes open. Balance Training Group Control GroupPretest Posttest Pretest Posttest Group Effect Time Effect Abs. Min. TTBML 1.22  T  0.37 1.36  T  0.53 1.12  T  0.18 1.23  T  0.26 0.50 0.38Abs. Min. TTBAP 4.14  T  1.47 4.13  T  0.95 3.48  T  0.87 4.22  T  0.79  j 0.11  j 0.006Mean Min. TTBML 4.56  T  1.59 5.09  T  2.38 4.29  T  1.15 4.53  T  1.13 0.50 0.33Mean Min. TTBAP 13.88  T  4.44 13.90  T  4.01 11.90  T  3.1 13.20  T  1.9 0.37 0.004SD Min. TTBML 3.35  T  1.42 4.48  T  2.98 3.25  T  1.22 3.62  T  1.27 0.68 0.80SD Min. TTBAP 9.07  T  3.16 8.43  T  3.26 8.01  T  2.45 7.93  T  1.67 0.30  j 0.20There were no significant changes in pretest to posttest for either group. Group effect sizes were calculated from posttest scores. Time effect sizes were calculated from the pretest andposttest measures of the balance training group.Abs., absolute; Min., minimum. BALANCE TRAINING AND ANKLE INSTABILITY Medicine & Science in Sports & Exercise d  1813 A P  P  L  I    E   D  S   C I    E  N  C E   S    Copyright @ 200 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. 8 Means and SD for all TTB measures in eyes-closed testingare listed in Table 3. Traditional COP-based measures.  There were nosignificant group    time interactions for any of thetraditional COP-based measures with eyes open; however,there was a significant time main effect for COP velocity inthe AP direction (  P   = 0.04).  Post hoc  comparisons revealedthat both groups had significant decreases in AP velocity inthe posttest compared with the pretest. There were no other significant interactions or main effects identified for theeyes-open tests (Table 4).For the eyes-closed trials, there was a significant group  time interaction for the COP velocity in the ML direction(  P   = 0.03).  Post hoc  comparisons revealed that the COPvelocity in the ML direction significantly decreased in the balance training group from pretest to posttest. There wereno significant changes within the control group or between-group comparisons pre- and posttest. There were no other significant interactions or main effects identified for theeyes-closed tests (Table 5). Dynamic Balance There were significant group    time interactions foundfor the PM (  P   = 0.01) and the PL reach (  P   = 0.03)components of the SEBT. In both directions, the balancetraining group had greater reach distances in the posttest measures compared with the pretest measures. Moreover,the balance training group reached farther than the controlgroup on posttest measures but not on pretest measures.There were no significant changes in the anterior reachdirection between pretest and posttest measures for either group (Table 6). DISCUSSION We found that 4 wk of balance training significantlyimproved self-reported function, static postural control asdetected by TTB measures, and dynamic postural control asassessed with the SEBT. These measures were specificallychosen to provide patient-oriented laboratory and clinicalevidence, respectively, of the effectiveness of balancetraining in this population with CAI.After undergoing 4 wk of balance training, individualswith CAI reported a significant improvement in self-reported function. The effect sizes for the pretest to posttest change for the balance training group on the FADI and theFADI Sport were 0.97 and 1.23, respectively. The effect sizes for the improvements in the FADI and the FADI Sport compared with the control group at posttest were 0.68 and1.58, respectively. The present study was a randomizedcontrolled trial in which one group was randomly chosen to participate in balance training and one was not. The controlgroup did not have a significant change in functional statusafter 4 wk, which indicates that the balance training waseffective in restoring self-reported function. Rozzi et al. (26)reported similar improvements on the Ankle Joint Func-tional Assessment Tool when comparing a group with CAIto a group of healthy controls who underwent balancetraining. They found that individuals who underwent 4 wk of training on the Biodex Stability System had improvementsin self-reported function, regardless of group membership. TABLE 3. Pretest and posttest measures of TTB in the ML and AP directions with eyes closed. Balance Training Group Control GroupPretest Posttest Pretest Posttest Group Effect Time Effect Abs. Min. TTBML 0.48  T  0.10 0.56  T  0.11*, †  0.52  T  0.13 0.50  T  0.10 0.60 0.80Abs. Min. TTBAP 1.63  T  0.63 1.74  T  0.61 1.51  T  0.51 1.50  T  0.47 0.51 0.17Mean Min. TTBML 1.84  T  0.53 2.15  T  0.61*, †  1.99  T  0.50 1.89  T  0.48 0.54 0.60Mean Min. TTBAP 5.32  T  1.77 6.04  T  1.88*, †  5.05  T  1.46 4.81  T  1.23 0.32 0.41SD Min. TTBML 1.61  T  0.66 2.05  T  0.99 1.66  T  0.51 1.69  T  0.70 0.51 0.67SD Min. TTBAP 3.11  T  1.06 3.91  T  1.20*, †  3.27  T  0.97 2.97  T  0.79 1.18 0.75There were significant group  time interactions for four of six measures. In all interactions, there was a significant increase in TTB measures at posttest for the balance training groupcompared with their respective pretest measures and the posttest measures of the control group,  P   G  0.05. Group effect sizes were calculated from posttest scores. Time effect sizeswere calculated from the pretest and posttest measures of the balance training group.Abs., absolute; Min., minimum.*  P   G  0.05 for pretest to posttest comparisons within the balance training group. †  P   G  0.05 for between-groups comparisons at posttest.TABLE 4. Pretest and posttest COP measures with eyes open. Balance Training Group Control GroupPretest Posttest Pretest Posttest Group Effect Time Effect COPML SD 0.19  T  0.04 0.18  T  0.05 0.19  T  0.03 0.18  T  0.03 0  j 0.20COPAP SD 0.24  T  0.06 0.26  T  0.06 0.27  T  0.07 0.26  T  0.05 0 0.33Range of COPML 0.87  T  0.18 0.85  T  0.23 0.91  T  0.12 0.87  T  0.12  j 0.16  j 0.11Range of COPAP 1.14  T  0.25 1.22  T  0.27 1.28  T  0.38 1.15  T  0.14 0.50 0.32Velocity of COPML 0.92  T  0.27 0.89  T  0.34 0.93  T  0.14 0.86  T  0.15 0.20  j 0.11Velocity of COPAP 0.76  T  0.27 0.74  T  0.26* 0.90  T  0.34 0.71  T  0.08* 0.38  j 0.07COP area 5.19  T  2.33 5.34  T  2.54 6.10  T  2.08 5.52  T  1.20  j 0.15 0.06There were no significant differences found for either group between pretest and posttest. Group effect sizes were calculated from posttest scores. Time effect sizes were calculatedfrom the pretest and posttest measures of the balance training group.An effect size of zero was calculated when the comparison means were equal.* Significantly decreased compared with pretest values, time main effect ( P   = 0.04). 1814  Official Journal of the American College of Sports Medicine       A      P      P      L      I      E      D      S      C      I      E      N      C      E      S
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