Athletic Training and Sports Health Care

Original Research 

Acquisition and Transfer of Postural Control Among Individuals With Chronic Ankle Instability Following a 3-Day Balance Training Program

Andrea L. Sulewski, MS, ATC, SCAT, CES; Brady L. Tripp, PhD, ATC; Erik A. Wikstrom, PhD, ATC

Abstract

Balance training has been suggested to improve postural control and reduce reinjury rates in those with chronic ankle instability (CAI). Typical balance training programs last several weeks, but recent evidence suggests that a 3-day balance training program may also improve postural control. Therefore, our primary purpose was to determine whether a 3-day balance training program improves balance in those with CAI. The secondary purpose was to determine whether attentional focus direction affects balance improvement magnitude. Two 16-participant cohorts were pretested and posttested on a Biodex Stability System and the Star Excursion Balance Test. The balance training cohort, divided into internal and external attentional focus groups, underwent twenty 20-second trials on level 6 of a Biodex Stability System for 3 consecutive days. The results indicate that 3 days of balance training failed to improve balance in those with CAI. Thus, balance training programs should be longer than 3 days.

Abstract

Balance training has been suggested to improve postural control and reduce reinjury rates in those with chronic ankle instability (CAI). Typical balance training programs last several weeks, but recent evidence suggests that a 3-day balance training program may also improve postural control. Therefore, our primary purpose was to determine whether a 3-day balance training program improves balance in those with CAI. The secondary purpose was to determine whether attentional focus direction affects balance improvement magnitude. Two 16-participant cohorts were pretested and posttested on a Biodex Stability System and the Star Excursion Balance Test. The balance training cohort, divided into internal and external attentional focus groups, underwent twenty 20-second trials on level 6 of a Biodex Stability System for 3 consecutive days. The results indicate that 3 days of balance training failed to improve balance in those with CAI. Thus, balance training programs should be longer than 3 days.

Ms Sulewski is from Myrtle Beach High School, Myrtle Beach, South Carolina; Dr Tripp is from the University of Florida, Gainesville, Florida; and Dr Wikstrom is from the University of North Carolina at Charlotte, Charlotte, North Carolina.

The authors have no financial or proprietary interest in the materials presented herein.

The authors thank Yong Woo An, MS, ATC, for his assistance with data collection.

Address correspondence to Andrea L. Sulewski, MS, ATC, SCAT, CES, Myrtle Beach High School, 3302 Robert Grissom Pkwy, Myrtle Beach, SC 29577; e-mail: asulewski@horrycountyschools.net.

Received: June 06, 2011
Accepted: August 31, 2011
Posted Online: October 17, 2011

Lateral ankle sprains are among the most frequent orthopedic injuries sustained during physical activity,1 accounting for approximately 25% of all sports-related injuries.2 Lateral ankle sprains are often considered a minor injury with no long-term consequences. However, research suggests up to 75% of people who sprain their ankle will develop chronic residual symptoms, commonly referred to as chronic ankle instability (CAI).3 Chronic ankle instability is characterized by pain and weakness,4 episodes of giving way,5 and recurrent injury.6 In addition, CAI negatively affects sensorimotor function at the local,7 spinal,8–11 and supraspinal12,13 levels. The most commonly reported sensorimotor impairment in those with CAI is postural control,9–11 and these impairments are associated with an increased risk of recurrent sprains.14,15

To treat sensorimotor dysfunction and postural control deficits, many clinicians use balance training as a therapeutic intervention. Balance training has been shown to improve postural control in those with CAI9–11 and reduce the recurrence of ankle injuries.14,16,17 Further, balance training has been shown to result in neural adaptations (eg, decreased spinal and motor cortex input as postural control improves) within the central nervous system.18,19 With mounting evidence suggesting that centrally mediated changes (eg, bilateral balance deficits) play a role in the development of CAI,12,13,20 the ability of balance training to cause neural adaptations at both the spinal and supraspinal level of the central nervous system may prove critical in providing better treatment for those with CAI. Although data from experimental studies support the use of balance training as a therapeutic intervention for the treatment of ankle joint pathologies, the exact dosage needed to obtain the above mentioned results remains unknown. However, it is generally accepted that balance training programs should be several weeks in duration and empirical data supports this hypothesis. For example, Zech et al21 demonstrated that balance training programs of 6 weeks or longer produce greater improvements than programs of 4 weeks in duration. Similarly, Bahr et al22 reported that the longer a balance training program is implemented, the greater preventative effects accrue from the program.

However, 2 recent investigations have reported postural control improvements in patients with acute ankle sprains after only 3 days of balance training.23,24 These investigations aimed to determine the most effective location of a patient’s attentional focus (internal versus external) on the acquisition, retention, and transfer of postural control skills during an intense albeit short balance training program. An internal attentional focus (IAF) is when the patient’s attention is directed toward himself or herself (eg, when the clinician instructs the patient to stand as still as possible during balance training exercises). An external attentional focus (EAF) is when the patient’s focus is directed on the effect of the movement (eg, when the clinician instructs the patient to keep the platform that the patient is standing on as still as possible during balance training exercises). Motor control research indicates that using an EAF is more effective at enhancing motor learning.25,26

Both investigations23,24 demonstrated that an EAF is more effective and resulted in greater acquisition, retention, and transfer of postural control skills in those with an acute ankle sprain. However, neither investigation incorporated a control group to determine whether the observed balance improvements were greater than the error associated with the measurement devices used, the natural recovery of a lateral ankle sprain, or both. The use of minimal detectable change (MDC) scores will determine whether balance improvements are greater than the error associated with the measurement devices used. Indeed, MDC scores determine how much an outcome measure needs to change following a rehabilitation intervention to be confidently considered a true change (ie, improvement or degradation) due to the intervention and not due to measurement error.27

Therefore, the primary purpose of this investigation was to determine whether a 3-day balance training program could cause balance improvements that exceed the calculated MDC scores among those with CAI. On the basis of clinical experience and the existing literature,18,19,21 we hypothesized that a 3-day balance training program would fail to cause balance improvements that exceeded the calculated MDC scores. The secondary aim of this investigation was to compare the effectiveness of an IAF and an EAF during the balance training program. We hypothesized that an EAF would result in greater acquisition and transfer of postural control skills.

Methods

Design and Participants

A total of 32 participants (men, n = 14; women, n = 18) with unilateral CAI (mean age = 25.3±4.7 years, mean height = 167.5±17.3 cm, mean weight = 75.4±12.9 kg), were recruited from the general student population at a major public university and volunteered to participate. Each participant met all of the following inclusion criteria: a history of lateral ankle sprain that required crutches or immobilization (eg, walking boot, ankle brace, elastic wrap, or non-weight bearing) for at least 2 days (mean days immobilized = 17.6±22.9); at least 1 recurrent sprain since the initial injury (mean recurrent sprains = 3.4±2.6); at least 1 episode of rolling or giving way since the initial injury (mean episodes of giving way = 10.6±10.2); and experiencing pain, instability, or weakness in the involved ankle that was attributed to the initial injury. For the purposes of this investigation, a patient’s reported use of crutches or immobilization was used to quantify a minimal level of severity for the initial lateral ankle sprain. However, the types of immobilization devices used by the participants was not recorded.

A recurrent ankle sprain was defined as an event that resulted in immediate disablement or immobilization. Rolling or giving way of the ankle was defined as when the ankle turned in but did not result in immediate disablement or immobilization (ie, the participant could continue with participation). All participants read and signed the university approved informed consent form prior to participation.

An initial cohort of 16 participants was recruited and equally divided into either the IAF or the EAF group. The first participant enrolled in this cohort was randomized using a coin flip, and all subsequent participants of this cohort were counterbalanced. Each participant in this cohort then attended 3 meetings held on consecutive days, as previously reported.23,24 A second cohort of 16 participants was then recruited and served as a control group. Each participant in this cohort then attended 2 meetings separated by 48 hours. The Figure illustrates the study design.

Flow chart of the 2 cohorts that participated in the current investigation. (Abbreviations: IAF, internal attentional focus; EAF, external attentional focus.)

Figure. Flow chart of the 2 cohorts that participated in the current investigation. (Abbreviations: IAF, internal attentional focus; EAF, external attentional focus.)

Procedures

All participants completed a baseline and posttest balance assessment on a Biodex Stability System (BSS)23,24 (Biodex Medical System Inc, Shirley, New York) and on a Star Excursion Balance Test (SEBT) grid. Balance assessments and training were completed on the BSS to provide a direct comparison with the previous investigations that used a 3-day balance training program.23,24 Thus, the BSS balance assessments in the training cohort quantified the acquisition of postural control as a result of the balance training program,23 whereas the SEBT was used to assess the transfer of postural control skill (ie, how well balance improvements in a trained task carry over to a different or untrained task). Transfer of postural control skills is important because not all balance training activities (eg, maintaining balance on an unstable platform) are representative of tasks completed during physical activity. The SEBT was chosen as the transfer test because it is a dynamic balance task, it has detected balance impairments associated with CAI,8,28 and balance training has resulted in improved SEBT scores in those with CAI.29

The BSS is an unstable support platform that tilts in any direction up to 20° and has 8 stability settings, with level 8 being the most stable and level 1 being the least stable.30 Main outcome measures included the overall stability index (OSI), the anterior–posterior stability index (APSI), and the medial–lateral stability index (MLSI). The OSI represents the total variance of platform displacement (all directions), measured in degrees, with higher scores indicating worse postural control, whereas the APSI and MLSI represent platform displacement in the sagittal and frontal planes, respectively.30,31 These measures are calculated using the following formulas:

  • OSI = [(Σ(0-Y)2 + Σ (0-X)2 / no. of samples)]^0.5.
  • APSI = [(Σ(0-Y)2/no. of samples)]^0.5.
  • MLSI = [(Σ(0-X)2/no. of samples)]^0.5.

Each BSS assessment consisted of two 20-second test trials using a stability level of 6, with a 30-second rest period between trials.23,24 The BSS test trials were preceded by 2 practice repetitions. Previous work has shown that this 4-trial protocol results in good to excellent reliability estimates, as measured with the intraclass correlation coefficient (ICC), for the OSI (ICC = 0.92), APSI (ICC = 0.89), and MLSI (ICC = 0.93).32 All participants were tested in their own athletic shoes while standing on their involved limb with their eyes open and their hands on their hips. Participants were tested shod so the results would be representative of an individual’s ability to balance during most recreational or competitive activities. A participant’s initial foot placement was determined according to manufacturer recommendations and patient comfort. Foot position was recorded to ensure consistency between practice repetitions, test trials, and balance training repetitions.31 In addition, the BSS computer interface was covered during all assessments and training to ensure that participants did not receive visual feedback during the test trials or training repetitions.31 The average of the 2 test trials from each assessment (baseline, posttest) was then used for further analysis. During test trials, participants were told that if they lost their balance (ie, put their contralateral limb down or used their hands to catch themselves on the hand rails), every effort should be made to return to the test position as quickly as possible. Participants were given these instructions so the postural instability would be reflected in the outcome scores, as opposed to the failed trial being discarded. Practice and training repetitions were conducted in the same way.

The SEBT grid is composed of 8 lines made with athletic tape extending out at 45° angles from each other.8,33 Participants reached in 3 of the 8 possible directions (anterior, posteriomedial, posteriolateral) in accordance with recommendations.33 Participants were instructed to reach as far as possible along each line and lightly touch the line with their toes before returning the reach leg to the center of the grid. During this procedure, participants maintained a single-leg stance on their involved limb in the center of the grid.7,33 Participants were required to keep their hands on their hips and to keep the heel of the stance leg on the ground at all times. Reach distances in all 3 directions were normalized to the participant’s leg length (anterior superior iliac spine to ipsilateral medial malleolus, measured with the patient supine). Two test trials were preceded by as many practice trials as the participants needed to feel comfortable with the test procedure. Hertel et al34 demonstrated that ICC values for all 8 directions of the SEBT ranged from 0.78 to 0.96. The average of the 2 normalized test trials was then used for further analysis.35 Participants received no directions regarding their attentional focus during any BSS or SEBT test trial.

The balance training protocol that the training cohort followed included twenty 20-second balance training repetitions, with a 30-second rest in between each repetition, for 3 consecutive days.23,24 Participants completed all balance training repetitions on the BSS, level 6, to replicate the previous investigations that used a 3-day balance training program.23,24 Prior to the first balance training repetition and after every second balance training repetition of each training session, participants received instructions regarding attentional focus based on group allocation. Participants in the IAF group were instructed to “keep your balance by stabilizing your body,” whereas those in the EAF group were instructed to “keep your balance by stabilizing the platform.”23,24

Statistical Analysis

To account for variations within the groups, pretest– posttest change scores were calculated for each dependent measure. To ascertain our primary aim, independent sample t tests were used to determine whether balance training, relative to the control group, resulted in greater acquisition of postural control, as measured by BSS scores (OSI, APSI, MLSI), and greater transfer of postural control, as measured by SEBT reach distances (anterior, posteriomedial, and posteriolateral). To achieve our secondary aim, independent sample t tests were used to determine the effect of attentional focus (IAF, EAF) on the acquisition and transfer of postural control skills. In addition, one-way ANOVAs were used to determine whether demographics or injury characteristics differed among the groups. A traditional alpha level of P ⩽ .05 was set a priori and used for all statistical analyses. Minimal detectable change (MDC) scores were also calculated using control group data to quantify the 95% confidence intervals of the included outcome’s measurement error.27 The MDC scores were calculated using the following formula: MDC = SEM×(2^0.5) × 1.96, where SEM represents the standard error of the measurement.27

Results

Table 1 shows participant demographics and injury characteristics for the EAF, IAF, and control groups. Only age differed among the groups, as the control group was significantly older than both the EAF and the IAF groups. The independent sample t tests revealed no significant differences between the balance training and control groups regarding both the acquisition and transfer of postural control skills (Table 2). Further, none of the pretest–posttest change scores for the balance training group exceeded the calculated MDC scores. Similarly, there were no differences between the EAF and IAF change scores (Table 3). In addition, none of the EAF or IAF change scores exceeded the calculated MDC scores.

Group Demographics and Injury Characteristics

Table 1: Group Demographics and Injury Characteristics

Pretest and Posttest Comparisons for the Balance Training and Control Groups for the Biodex Stability Systema and Star Excursion Balance Test Outcome Measures

Table 2: Pretest and Posttest Comparisons for the Balance Training and Control Groups for the Biodex Stability System and Star Excursion Balance Test Outcome Measures

Pretest and Posttest Comparisons for the Internal and External Attentional Focus Groups for the Biodex Stability Systema and Star Excursion Balance Test Outcome Measures

Table 3: Pretest and Posttest Comparisons for the Internal and External Attentional Focus Groups for the Biodex Stability System and Star Excursion Balance Test Outcome Measures

Discussion

The primary purpose of this investigation was to determine whether a 3-day balance training program23,24 could cause balance improvements that exceeded measurement error, as calculated by MDC scores, in those with CAI. The current results indicate that a 3-day balance training program does not improve postural control to a level greater than the calculated MDC scores for the outcomes used in this investigation, which supports the a priori hypothesis. Further, the finding suggests that any observed improvements, even those not statistically significant, are most likely due to measurement error27 and that a 3-day balance training program is ineffective for those with CAI.

Our level 6 BSS means were much lower (ie, indicating better balance) than the level 7 BSS means reported by Rahnama et al (OSI = 8.58; APSI = 6.95; MLSI = 5.38).36 This difference may be explained by several factors; however, the most likely factors include the more stable platform setting used in the current investigation and the differences in the magnitude of CAI-related balance impairments between the samples tested. However, our anterior SEBT reach mean is comparable with previous reports (76%33 and 79%37), whereas our posteriomedial and posteriolateral SEBT reach means are similar to those reported by Hertel et al (85% and 79%, respectively)14 but lower than those reported by Hoch and McKeon (93% and 87%, respectively).37 Further, our calculated MDC scores are much higher than those previously reported for the SEBT (anterior = 1.81%; posteriomedial = 3.16%; posteriolateral = 5.25%),37 suggesting greater variability in the current SEBT scores over time. The cumulative variability in the BSS and SEBT outcomes suggests that more stable balance measures (eg, center of pressure or time-to-boundary) may need to be used in future investigations to more accurately determine the effectiveness of short-term balance training interventions.

However, the balance training program used in the current investigation has been reported to improve the acquisition, retention, and transfer of postural control skills in patients with acute ankle sprains.23,24 The acquisition improvements (average OSI = 1.54; average APSI = 1.36; average MLSI = 0.65)23 occurred regardless of the attentional focus strategy used (EAF, IAF). However, neither investigation incorporated a control group. Thus, it was unclear whether the observed improvements were the result of the balance training program or the natural recovery of postural control deficits associated with acute lateral ankle sprains over the duration of the investigation. In the current study, we chose to investigate those with CAI because they are more readily available than those with acute ankle sprains, have known balance impairments,9–11 and respond to balance training as a therapeutic intervention.11

Our results demonstrate much smaller BSS improvements following a 3-day balance training program (OSI [0.40], APSI [0.20], MLSI [0.06]) than those previously reported.23,24 This was not unexpected, given that those with acute ankle sprains have greater postural impairments than those with CAI.11 Unfortunately, the 3-day balance training program failed to improve the BSS and SEBT outcomes relative to the control group, and the observed changes failed to exceed the measurement error associated with the selected outcomes. Thus, these results suggest that a 3-day balance training program is insufficient to improve BSS and SEBT outcomes in those with CAI. Because those with CAI have smaller postural control deficits than those with acute ankle sprains, future research is needed to determine whether a more challenging (eg, level 2 of the BSS) balance training program could result in balance improvements in those with CAI during a short (eg, 3-day) balance training intervention. These current results also imply that the previously reported balance improvements in those with acute ankle sprains23,24 may have been the result of the natural recovery process of an acute ankle sprain and not the result of the completed balance training program. However, only future research using individuals with acute lateral ankle sprains who are randomized to training and control groups can provide a definitive answer. It is important to note that despite the nonsignificant findings, short-term motor adaptations (eg, suppression of the Hoffman reflex38,39) may have occurred. These adaptations, often called a learning effect, would serve as the foundation for long-term balance improvements if the balance training intervention duration was extended.

Our results also suggest that the direction of a participant’s attentional focus (EAF or IAF) does not influence balance acquisition or transfer in those with CAI. The direction of a participant’s attentional focus has been of particular interest, primarily in the field of motor control, in an effort to optimize the learning or refinement of motor skills. Research using healthy uninjured control-participants indicates that balance may be learned more effectively if a participant uses an EAF.25,26 Use of an EAF is hypothesized to facilitate more efficient movement patterns by facilitating the automation of the sensorimotor system.40 However, both our sample size (n = 8 per group) and study duration (3 days) may have limited our ability to detect attentional focus strategy differences. Previous investigations26,40 have used center of pressure outcomes from an instrumented force platform, which suggests that the precision of the selected outcomes may have also played in role in lack of differences between the IAF and the EAF groups. In other words, center of pressure outcomes may be more precise and therefore better able than BSS and SEBT outcomes to detect differences in training improvements between the IAF and the EAF groups.

Implications for Clinical Practice

This study revealed that a 3-day balance training program does not improve postural control in those with CAI. However, current research has demonstrated clear improvements for those with CAI after completing balance training programs of 4–6 weeks or longer. As a result, we recommend that clinicians continue to use balance training programs of at least 4–6 weeks in duration to facilitate the return of postural control after an injury.

Conclusion

The completion of a 3-day balance training program does not improve postural control in those with CAI. Specifically, the completion of sixty 20-second single leg stance trials over 3 days on a relatively firm (level 6) BSS platform could not improve the selected outcomes (ie, OSI, MLSI, APSI, and SEBT reach distances) beyond the calculated MDC scores. As a result, additional research regarding the effectiveness of balance training programs with a short- and mid-range duration (eg, 3 days to 2 weeks), as well as more challenging protocols, is needed.

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Group Demographics and Injury Characteristics

IAF (N = 8)aEAF (N = 8)aCONTROL (N = 16)aF(2,23)P
Age (years)21.1±2.422.3±3.826.6±5.25.3.01
Height (cm)173.7±8.3166.1±7.5171.9±11.71.3.29
Weight (kg)87.1±15.974.8±20.971.4±14.32.4.11
No. of days on crutches or immobilized following initial injury13.3±18.28.6±6.925.8±29.41.7.20
No. of recurrent sprains since initial injury2.4±0.75.6±8.13.6±2.01.2.31
No. of giving way episodes since initial injury9.1±10.210.5±7.912.1±12.40.2.82

Pretest and Posttest Comparisons for the Balance Training and Control Groups for the Biodex Stability Systema and Star Excursion Balance Test Outcome Measures

OUTCOMEPRETESTaPOSTTESTaCHANGE SCORE (95% CI)bPMDC
Overall stability index (°)
  Training3.0±1.02.6±1.0−0.4±0.6 (−0.7 to 0.1).162.06
  Control3.3±1.23.6±1.20.04±1.0 (−0.6 to 0.5)
Anterioposterior stability index (°)
  Training2.3±0.62.1±0.8−0.2±0.5 (−0.5 to 0.1).301.92
  Control2.6±1.22.7±0.90.06±1.01 (−0.5 to 0.6)
Mediolateral stability index (°)
  Training2.1±0.91.6±0.6−0.5±0.7 (−0.9 to 0.1).101.16
  Control2.0±0.81.9±1.0−0.27±0.8 (−0.7 to 0.2)
Anterior reach (%)
  Training73.6±6.876.5±7.02.6±4.4 (0.3 to 4.9).587.29
  Control83.1±6.284.8±5.91.7±4.9 (−0.9 to 4.3)
Posteriomedial reach (%)
  Training83.8±11.490.5±10.85.0±3.0 (3.3 to 6.6).257.96
  Control83.7±12.586.8±12.13.1±5.6 (0.1 to 6.1)
Posteriolateral reach (%)
  Training78.2±10.884.9±9.55.3±3.0 (3.6 to 6.9).2710.42
  Control78.8±12.983.4±12.93.4±5.9 (0.3 to 6.5)

Pretest and Posttest Comparisons for the Internal and External Attentional Focus Groups for the Biodex Stability Systema and Star Excursion Balance Test Outcome Measures

OUTCOMEPRETESTbPOSTTESTbCHANGE SCORE (95% CI)bPMDC
Overall stability index (°)
  Internal focus3.4±1.13.1±0.90.22±0.41 (−0.1 to 0.6).272.06
  External focus2.6±0.82.1±0.70.55±0.71 (−0.1 to 1.1)
Anterioposterior stability index (°)
  Internal focus2.6±0.72.6±0.70.12±0.62 (−0.4 to 0.6).481.92
  External focus2.0±0.41.7±0.50.31±0.47 (−0.1 to 0.7)
Mediolateral stability index (°)
  Internal focus2.2±1.01.8±0.70.44±0.75 (−0.2 to 1.1).881.16
  External focus1.9±0.71.4±0.30.50±0.79 (−0.2 to 1.2)
Anterior reach (%)
  Internal focus72.6±7.675.3±7.22.31±4.17 (−1.2 to 5.8).787.29
  External focus74.6±6.477.7±7.12.93±4.81 (−1.1 to 6.9)
Posteriomedial reach (%)
  Internal focus84.1±13.392.0±12.45.17±2.68 (2.9 to 7.4).837.96
  External focus83.4±10.188.9±9.64.82±3.50 (1.8 to 7.7)
Posteriolateral reach (%)
  Internal focus79.3±12.286.2±10.25.01±2.83 (2.6 to 7.4).7310.42
  External focus77.3±10.083.6±9.25.56±3.42 (2.7 to 8.4)
Authors

Ms Sulewski is from Myrtle Beach High School, Myrtle Beach, South Carolina; Dr Tripp is from the University of Florida, Gainesville, Florida; and Dr Wikstrom is from the University of North Carolina at Charlotte, Charlotte, North Carolina.

The authors have no financial or proprietary interest in the materials presented herein.

Address correspondence to Andrea L. Sulewski, MS, ATC, SCAT, CES, Myrtle Beach High School, 3302 Robert Grissom Pkwy, Myrtle Beach, SC 29577; e-mail: asulewski@horrycountyschools.net

10.3928/19425864-20111017-01

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