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Jay Hertel, Lauren C. Olmsted-Kramer and John H. Challis

A novel approach to quantifying postural stability in single leg stance is assessment of time-to-boundary (TTB) of center of pressure (COP) excursions. TTB measures estimate the time required for the COP to reach the boundary of the base of support if it were to continue on its instantaneous trajectory and velocity, thus quantifying the spatiotemporal characteristics of postural control. Our purposes were to examine: (a) the intrasession reliability of TTB and traditional COP-based measures of postural control, and (b) the correlations between these measures. Twenty-four young women completed three 10-second trials of single-limb quiet standing on each limb. Traditional measures included mean velocity, standard deviation, and range of mediolateral (ML) and anterior-posterior (AP) COP excursions. TTB variables were the absolute minimum, mean of minimum samples, and standard deviation of minimum samples in the ML and AP directions. The intrasession reliability of TTB measures was comparable to traditional COP based measures. Correlations between TTB and traditional COP based measures were weaker than those within each category of measures, indicating that TTB measures capture different aspects of postural control than traditional measures. TTB measures provide a unique method of assessing spatiotemporal characteristics of postural control during single limb stance.

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Cameron Powden and Matthew Hoch

Context:

Currently, there are limited guidelines for the trial duration of quiet single-limb postural control tests. However, trial duration may influence the results of postural control assessments.

Objective:

To examine the effect of trial duration on instrumented measures of postural control in healthy adults.

Design:

Cross-sectional.

Setting:

Laboratory.

Patients or Other Participants:

Ten healthy adults (eight females, two males; age = 22.1 ± 1.5 years; 167.4 ± 9.3 cm; 67.4 ± 12.3 kg).

Interventions:

Static postural control was assessed using quiet single-limb stance on a force plate. With eyes open and closed, participants stood barefoot on one limb. Instructions were stand with hands on hips and remain as motionless as possible. A practice trial was performed before the collection of three 10 s trials on each limb for each visual condition. The data collected during each trial were analyzed as the initial 2.5 s, the initial 5 s, and 10 s.

Main outcome Measures:

The independent variables included vision, limb, and trial duration. The dependent variables included postural control examined using time-to-boundary (TTB) variables: mean of TTB minima (TTB-M) and the standard deviation of TTB minima (TTB-SD) in the anterior-posterior (AP) and medial-lateral (ML) directions.

Results:

No significant 3-way or 2-way interactions or limb main effects were identified. Main effects were identified for vision and trial duration in all TTB variables. Post hoc analysis revealed significant differences between all trial durations in all TTB variables.

conclusions:

Greater TTB values were exhibited during the 10 s trial durations compared with 5 s and 2.5 s, and 5 s trial durations compared with 2.5 s, indicating postural control improved with longer trial durations. This suggests differing aspects of postural control may be examined with different trial durations.

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Masafumi Terada, Megan Beard, Sara Carey, Kate Pfile, Brian Pietrosimone, Elizabeth Rullestad, Heather Whitaker and Phillip Gribble

understanding of the influence of LAS on postural control. Nonlinear dynamic measures such as time-to-boundary (TTB) and sample entropy (SampEn) analysis, which quantify the structure or organization of the postural control variability ( Glass, Ross, Arnold, & Rhea, 2014 ; Hertel & Olmsted-Kramer, 2007

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Kyung-Min Kim, Joo-Sung Kim, Jeonghoon Oh and Dustin R. Grooms

milliseconds at a time. 9 Participants performed bipedal stances that lasted for 20 seconds and were repeated 3 times. The averages were used for statistical analysis. The study outcomes were time-to-boundary (TTB) parameters of center-of-pressure excursion. We computed TTB measures such as mean and SD of the

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Joshua J. Liddy, Amanda J. Arnold, HyeYoung Cho, Nathaniel L. Romine and Jeffrey M. Haddad

important for organizing postural responses, such as initiating a step. 21 Postural time-to-boundary measures a temporal margin of safety by determining how long it would take the CoP to reach the base of support based on its instantaneous position, velocity, and acceleration. 22 , 23 As a complementary

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Stephen C. Cobb, Mukta N. Joshi, David M. Bazett-Jones and Jennifer E. Earl-Boehm

The effect of time-to-boundary minima selection and stability limit definition was investigated during eyes open and eyes closed condition single-limb stance postural stability. Anteroposterior and mediolateral time-to-boundary were computed using the mean and standard deviation (SD) of all time-to-boundary minima during a trial, and the mean and SD of only the 10 absolute time-to-boundary minima. Time-to-boundary with rectangular, trapezoidal, and multisegmented polygon defined stability limits were also calculated. Spearman’s rank correlation coefficient test results revealed significant medium-large correlations between anteroposterior and mediolateral time-to-boundary scores calculated using both the mean and SD of the 10 absolute time-to-boundary minima and of all the time-to-boundary minima. Friedman test results revealed significant mediolateral time-to-boundary differences between boundary shape definitions. Follow-up Wilcoxon signed rank test results revealed significant differences between the rectangular boundary shape and both the trapezoidal and multisegmented polygon shapes during the eyes open and eyes closed conditions when both the mean and the SD of the time-to-boundary minima were used to represent postural stability. Significant differences were also revealed between the trapezoidal and multisegmented polygon definitions during the eyes open condition when the SD of the time-to-boundary minima was used to represent postural stability. Based on these findings, the overall results (i.e., stable versus unstable participants or groups) of studies computing postural stability using different minima selection can be compared. With respect to boundary shape, the trapezoid or multisegmented polygon shapes may be more appropriate than the rectangular shape as they more closely represent the anatomical shape of the stance foot.

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Matthew C. Hoch, David R. Mullineaux, Richard D. Andreatta, Robert A. English, Jennifer M. Medina-McKeon, Carl G. Mattacola and Patrick O. McKeon

Context:

A single talocrural joint-mobilization treatment has improved spatiotemporal measures of postural control but not ankle arthrokinematics in individuals with chronic ankle instability (CAI). However, the effects of multiple treatment sessions on these aspects of function have not been investigated.

Objective:

To examine the effect of a 2-wk anterior-to-posterior joint-mobilization intervention on instrumented measures of single-limb-stance static postural control and ankle arthrokinematics in adults with CAI.

Design:

Repeated measures.

Setting:

Research laboratory.

Participants:

12 individuals with CAI (6 male, 6 female; age 27.4 ± 4.3 y, height 175.4 ± 9.78 cm, mass 78.4 ± 11.0 kg).

Intervention:

Subjects received 6 treatments sessions of talocrural grade II joint traction and grade III anterior-to-posterior joint mobilization over 2 wk.

Main Outcome Measures:

Instrumented measures of single-limb-stance static postural control (eyes open and closed) and anterior and posterior talar displacement and stiffness were assessed 1 wk before the intervention (baseline), before the first treatment (preintervention), 24–48 h after the final treatment (postintervention), and 1 wk later (1-wk follow-up). Postural control was analyzed as center-of-pressure velocity, center-of-pressure range, the mean of time-to-boundary minima, and standard deviation of time-to-boundary minima in the anteroposterior and mediolateral directions for each visual condition.

Results:

No significant differences were identified in any measures of postural control (P > .08) or ankle arthrokinematics (P > .21).

Conclusions:

The 2-wk talocrural joint-mobilization intervention did not alter instrumented measures of single-limb-stance postural control or ankle arthrokinematics. Despite the absence of change in these measures, this study continues to clarify the role of talocrural joint mobilization as a rehabilitation strategy for patients with CAI.

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Christopher J. Burcal, Alejandra Y. Trier and Erik A. Wikstrom

Context:

Both balance training and selected interventions meant to target sensory structures (STARS) have been shown to be effective at restoring deficits associated with chronic ankle instability (CAI). Clinicians often use multiple treatment modalities in patients with CAI. However, evidence for combined intervention effectiveness in CAI patients remains limited.

Objective:

To determine if augmenting a balance-training protocol with STARS (BTS) results in greater improvements than balance training (BT) alone in those with CAI.

Design:

Randomized-controlled trial.

Setting:

Research laboratory.

Patients:

24 CAI participants (age 21.3 ± 2.0 y; height 169.8 ± 12.9 cm; mass 72.5 ± 22.2 kg) were randomized into 2 groups: BT and BTS.

Interventions:

Participants completed a 4-week progression-based balance-training protocol consisting of 3 20-min sessions per week. The experimental group also received a 5-min set of STARS treatments consisting of calf stretching, plantar massage, ankle joint mobilizations, and ankle joint traction before each balance-training session.

Main Outcome Measures:

Outcomes included self-assessed disability, Star Excursion Balance Test reach distance, and time-to-boundary calculated from static balance trials. All outcomes were assessed before, and 24-hours and 1-week after protocol completion. Self-assessed disability was also captured 1-month after the intervention.

Results:

No significant group differences were identified (P > .10). Both groups demonstrated improvements in all outcome categories after the interventions (P < .10), many of which were retained at 1-week posttest (P < .10). Although 90% CIs include zero, effect sizes favor BTS. Similarly, only the BTS group exceeded the minimal detectable change for time-to-boundary outcomes.

Conclusions:

While statistically no more effective, exceeding minimal detectable change scores and favorable effect sizes suggest that a 4-week progressive BTS program may be more effective at improving self-assessed disability and postural control in CAI patients than balance training in isolation.

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Patrick O. McKeon, Alex J. Stein, Christopher D. Ingersoll and Jay Hertel

Context:

Postural control as assessed via time-to-boundary (TTB) measures has been shown to be impaired in those with chronic ankle instability (CAI). Foot orthotics have been shown to improve postural control, although it is not clear if this is via mechanical or sensorimotor mechanisms.

Objective:

To assess the effect of textured shoe inserts that provide no mechanical support on postural control as assessed by TTB measures in subjects with CAI.

Design:

A crossover design to examine the effects of a textured insole on postural control in individuals with unilateral CAI. The independent variables were vision (eyes open, eyes closed) and texture (textured insole, sham insole, control).

Setting:

Laboratory.

Participants:

20 physically active individuals, 12 men, 8 women, age 18–45 y (21.5 ± 5.51) with self-reported CAI.

Intervention:

Each subject balanced in shod single-limb stance with eyes open and eyes closed under 3 conditions (control, sham, and textured insole). The order of testing under the 3 shoe conditions and 2 vision conditions was counterbalanced.

Main Outcome Measures:

The mean of TTB minima and the standard deviation of TTB minima in the mediolateral (ML) and anteroposterior directions.

Results:

There were significant reductions in TTB ML magnitude and variability found in the textured condition compared with the control and sham conditions. In the textured condition, subjects failed significantly more trials than any other condition.

Conclusions:

Stimulating the plantar surface of the foot, via a textured insole, has an effect in the broad spectrum of postural-control maintenance in individuals with CAI.

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Cameron J. Powden, Kathleen K. Hogan, Erik A. Wikstrom and Matthew C. Hoch

Context:

Talocrural joint mobilizations are commonly used to address deficits associated with chronic ankle instability (CAI).

Objective:

Examine the immediate effects of talocrural joint traction in those with CAI.

Design:

Blinded, crossover.

Setting:

Laboratory.

Participants:

Twenty adults (14 females; age = 23.80 ± 4.02 y; height = 169.55 ± 12.38 cm; weight = 78.34 ± 16.32 kg) with self-reported CAI participated. Inclusion criteria consisted of a history of ≥1 ankle sprain, ≥2 episodes of giving way in the previous 3 mo, answering “yes” to ≥4 questions on the Ankle Instability Instrument, and ≤24 on the Cumberland Ankle Instability Tool.

Intervention:

Subjects participated in 3 sessions in which they received a single treatment session of sustained traction (ST), oscillatory traction (OT), or a sham condition in a randomized order. Interventions consisted of four 30-s sets of traction with 1 min of rest between sets. During ST and OT, the talus was distracted distally from the ankle mortise to the end-range of accessory motion. ST consisted of continuous distraction and OT involved 1-s oscillations between the mid and end-range of accessory motion. The sham condition consisted of physical contact without force application. Preintervention and postintervention measurements of weight-bearing dorsiflexion, dynamic balance, and static single-limb balance were collected.

Main Outcome Measures:

The independent variable was treatment (ST, OT, sham). The dependent variables included pre-to-posttreatment change scores for the WBLT (cm), normalized SEBTAR (%), and time-to-boundary (TTB) variables(s). Separate 1-way ANOVAs examined differences between treatments for each dependent variable. Alpha was set a priori at P < .05.

Results:

No significant treatment effects were identified for any variables.

Conclusion:

A single intervention of ST or OT did not produce significant changes in weight-bearing dorsiflexion range of motion or postural control in individuals with CAI. Future research should investigate the effects of repeated talocrural traction treatments and the effects of this technique when combined with other manual therapies.