A new approach of the Star Excursion Balance Test to assess dynamic postural control in people complaining from chronic ankle instability

The purpose of this study was to quantitatively and qualitatively assess dynamic balance with accuracy in individuals with chronic ankle instability (CAI). To this aim, a motion capture system was used while participants performed the Star Excursion Balance Test (SEBT). Reached distances for the 8 points of the star were automatically computed, thereby excluding any dependence to the experimenter. In addition, new relevant variables were also computed, such as absolute time needed to reach each distance, lower limb ranges of motion during unipodal stance, as well as absolute error of pointing. Velocity of the center of pressure and range of variation of ground reaction forces have also been assessed during the unipodal phase of the SEBT thanks to force plates. CAI group exhibited smaller reached distances and greater absolute error of pointing than the control group (p < 0.05). Moreover, the ranges of motion of lower limbs joints, the velocity of the center of pressure and the range of variation of the ground reaction forces were all significantly smaller in the CAI group (p < 0.05). These reduced quantitative and qualitative performances highlighted a lower dynamic postural control. The limited body movements and accelerations during the unipodal stance in the CAI group could highlight a protective strategy. The present findings could help clinicians to better understand the motor strategies used by CAI patients during dynamic balance and may guide the rehabilitation process.     

Kinematic and kinetic factors associated with leg reach asymmetry during the Star Excursion Balance Test in division I athletes

ObjectivesTo explore which balance and movement factors contribute most to reach distance asymmetry during the Star Excursion Balance Test (SEBT) in Division I athletes.DesignCross-Sectional Study.SettingRehabilitation Biomechanics Laboratory, NCAA Division I Athletics Program.Participants36 Division I athletes (20 Male; 16 Female).Main outcome measuresCenter of Pressure, Kinematic and Kinetic variables were measured during performance of anterior, Posterior-Medial (PM), and Posterior-Lateral (PL) directions of the SEBT in order to determine which factors predict reach distance asymmetry.ResultsCOP variables approached significance in predicting asymmetry for the anterior direction (p <0.08), kinematic variables approached significance in predicting asymmetry in the PL direction (p < 0.06), and kinetic variables were significant in predicting asymmetry in the PM direction (p < 0.03).ConclusionsFindings suggest that different strategies could be used to improve leg reach asymmetry based on specific direction of the asymmetry. Improving ability to control COP area seems to be important for the anterior direction, while control of limb movement seems to be most important for leg reach asymmetry in the PM and PL directions.     

Increase in muscle tone promotes the use of ankle strategies during perturbed stance

Background:To maintain an upright standing posture against external disturbances, the human body mainly employs two types of postural control strategies: “ankle strategy” and “hip strategy.” While it has been reported that the magnitude of the disturbance alters the use of postural control strategies, it has not been elucidated how the level of muscle tone, one of the crucial parameters of bodily function, determines the use of each strategy. We have previously confirmed using forward dynamics simulations of human musculoskeletal models that an increased muscle tone promotes the use of ankle strategies. The objective of the present study was to experimentally evaluate a hypothesis: an increased muscle tone promotes the use of ankle strategies.Research question:Do changes in the muscle tone affect the use of ankle strategies?Methods:Participants were asked to maintain their standing posture on a movable platform sliding horizontally at several accelerations. Postural reactions for support surface translations were examined under three instructions with or without handgrips: relax state, squeezing a handgrip, and an increased muscle tone of the whole body. Surface-electromyography and marker locations of joints were measured to calculate the index of muscle tone and postural control strategies. The relationship of the indexes was evaluated based on correlation coefficients.Results:In half of the conditions, weak negative correlations were noted between the muscle tone index and postural control strategy index. In other words, an increased muscle tone rather promoted the use of the ankle strategy than the hip strategy. These findings are consistent with our previous simulation results.Significance:The results recognized a positive response to the research question. This suggests that it is crucial to take muscle tone into account to understand postural control strategies.     

Effects of simulated peripheral visual field loss on the static postural control in young healthy adults

BackgroundIntegration of visual, vestibular, and proprioceptive sensations contributes to postural control. People with peripheral visual field loss have serious postural instability. However, the directional specificity of postural stability and sensory reweighting caused by gradual peripheral visual field loss remain unclear.Research questionWhat are the effects of peripheral visual field loss on static postural control?MethodsFifteen healthy young adults participated in this study. The participants were asked to stand quietly on a foam surface. Three conditions of virtual visual field loss (90°, 45°, and 15°) were provided by a head-mounted display, and ground reaction forces were collected using a force plate to calculate the displacements of the center of pressure (COP).ResultsThe root mean square (RMS), mean velocity, and 95% ellipse area of COP displacements in the horizontal plane increased, and RMS in the anteroposterior (AP) direction was unchanged under the smallest visual field condition compared to the largest one. The power spectrum density of COP displacements in the low-frequency band was decreased and that in the medium-frequency band was increased in the AP direction.SignificanceDuring quiet standing of young healthy adults with peripheral visual field loss, increased peripheral visual field loss resulted in lower postural stability. Postural stability in the AP direction was maintained contrary to the functional sensitivity hypothesis. Peripheral visual field loss reduced the weighting of the visual input and increased that of the vestibular input in the AP direction to maintain equilibrium.     

Visual feedback in the lower visual field affects postural control during static standing

BackgroundThe dorsal parietal visual system plays an important role in self-motion perception and spatial cognition. It also strongly responds to visual inputs from the lower visual field. Postural control is modified in a process called sensory reweighting based on the reliability of available sensory sources. The question of whether visual stimuli presented to either the lower or upper visual field affect postural control and sensory reweighting has not been resolved.Research questionDo visual stimuli presented to the lower and upper visual fields affect postural control and sensory reweighting?MethodsTwenty-nine healthy young adults participated in the study. Four conditions (full visual field, upper visual field, lower visual field, and no optic flow condition) were simulated in a VR environment using a head-mounted display. The optic flow stimuli used were swarms of small white spheres originating from the central point of the visual field, moving radially towards the periphery, and expanding across the scene. Participants were instructed to stand quietly for 50 s under each visual condition. Using force plate signals, we measured the center of pressure (COP) signal in the horizontal plane and calculated its 95 % ellipse area, root mean square (RMS) deviations, the mean velocity, and power spectral density (PSD).ResultsOptic flow in the full and lower visual fields produced significantly smaller 95 % ellipse area and RMS of COP in the anterior-posterior direction compared to optic flow in the upper visual field. Furthermore, the PSD of the lower frequency band (0–0.3 Hz) was decreased and that of higher frequency bands (0.3–1 Hz and 1–3 Hz) was increased for the lower compared to the upper visual field.SignificanceVisual feedback affects static postural control more when presented in the lower visual field compared to the upper visual field.     

Lateral ankle sprain alters postural control in bipedal stance – part 1: restoration over the 30 days following the injury

The time evolution of the postural behavior of 23 lateral ankle sprain patients (degrees I and II) were evaluated 14 h and 10 and 30 days on average after their injury and compared with those of 30 age‐matched healthy individuals. The patients were tested with separate measurements of the reaction forces under each limb to highlight the possible compensatory mechanisms between the sound and the injured legs. Their postural behavior in bipedal stance was characterised by a weight‐bearing asymmetry with more weight on the sound leg and an asymmetry of the postural stabilisation mechanisms, which are limited and perturbed under the injured leg. Pain appears to be the main factor for explaining these postural asymmetries. Despite these asymmetries, the patients were nonetheless more unstable than the individuals constituting the group control. Ten days later, only the weight‐bearing asymmetry was still observed whereas 30 days later, the postural behavior was totally normal once again. Lateral ankle sprain perturbs the contribution of the injured leg in postural stabilisation, inducing a larger involvement of the sound leg in the postural stability process. These characteristics are largely reduced 10 days after the injury.     

Performance and reliability of the Lower Quarter Y Balance Test in healthy adolescents from grade 6 to 11

BackgroundThe Lower Quarter Y Balance Test (YBT-LQ) has been widely used in the field to assess dynamic balance performance in various populations. However, no study has demonstrated test-retest reliability of the YBT-LQ in adolescents including several age cohorts, even though reliability is necessary to provide repeatable performance data.ObjectiveThus, we examined test-retest reliability of the YBT-LQ in healthy adolescents.MethodsIn a school setting, 178 secondary school students (93 female, 85 male) in sixth to eleventh grades (11–19 years) performed the YBT-LQ twice, 7 days apart. Normalized maximal reach distances (% leg length) for all three directions (i.e., anterior, posterolateral, posteromedial) and both legs and the composite score were used as outcome measures. Intraclass correlation coefficient (ICC_3,1) and standard error of measurement (SEM) were calculated to assess relative and absolute test-retest reliability, respectively. Practical relevance of the YBT-LQ was determined by calculating the minimal detectable change (MDC_95%).ResultsIrrespective of grade, test-retest reliability for all distances reached was predominately "excellent" (i.e., ICC_3,1 > 0.75) and the rather small SEM values ranged from 1.77 to 5.81%. Depending on grade and reach direction, MDC values of 4.90 to 16.10% represent the minimum amount of change needed to identify clinically relevant effects in repeated measurements of the YBT-LQ performance.ConclusionsThe observed values suggest that the YBT-LQ is a reliable test and suitable to detect changes of dynamic balance performance in healthy adolescents from grade six to eleven (i.e., aged 11–19 years).     

Dynamic postural control during (in)visible curb descent at fast versus comfortable walking velocity

BackgroundThe unexpectedness of ground-contact onset in stepping down due, e.g., to a camouflaged curb during ongoing gait may impose potential postural control challenges, which might be deteriorated when walking faster.Research questionDoes traversing camouflaged versus visible curbs, at a fast walking velocity, induce more unstable body configurations, assessed by a smaller anteroposterior “margin of stability” (MoS)?MethodsFor twelve healthy participants, we investigated MoS at foot touchdown in descent and in the first recovery step from 0- and 10-cm visible and camouflaged curbs at comfortable (1.22 ± 0.08 m/s) and fast (1.71 ± 0.11 m/s) walking velocities. Three-way (velocity, elevation, visibility) and two-way (velocity, visibility) repeated-measurement ANOVAs were performed to determine their interactions on MoS, and its determining parameters, during curb negotiation and recovery step, respectively.ResultsNo greater postural instability when traversing a camouflaged versus visible curb at a faster walking velocity during curb descent, indicated by no three-way interaction effects on MoS. However, an elevation-by-visibility interaction showed a dramatic decrease of MoS when descending a 10-cm camouflaged versus visible curb. This was because of a farther anterior displacement of center-of-mass with a larger velocity. Furthermore, the walking velocity was independently associated with a smaller MoS and a more anteriorly-shifted center-of-mass with a higher velocity. In the recovery step, participants demonstrated a reduced stability of the body configuration when walking faster or recovering from a camouflaged than from a visible curb. The mentioned result implies that the potential to increase the base-of-support to compensate for an increased center-of-mass velocity, induced by an increased walking velocity, is limited.SignificanceDespite a significant independent main effect of walking velocity, a more unstable postural control observed during traversing of camouflaged versus visible curbs was found not to be walking velocity-related in young individuals. Further research, including elderly may shed more light on these results.     

Rating of perceived exertion (RPE) in studies of fatigue-induced postural control alterations in healthy adults: Scoping review of quantitative evidence

BackgroundAmongst the literature researching the effects of exercise-induced fatigue on postural control in healthy adults, many studies have used the Borg scales to document the rating of perceived exertion (RPE) and have shown a broad range of RPE values. Our main aim was to map fatigue-induced RPE values in included publications. Secondary aims were to summarize the preference and purpose for the use of Borg scales within the included publications and to explore the potential associations between fatigue-induced RPE values and postural control changes.MethodsFive databases (Ovid Medline, PubMed, CINAHL, Scopus, and SPORTDiscus) were systematically searched for synthesizing data among the publications that reported RPE values on the Borg RPE- and Category-Ratio (CR) 10 scales and also found fatigue effects on postural control in healthy adults. Spearman’s rank correlations were conducted to assess potential associations between fatigue-induced RPE values and maximal postural control changes across the included publications (group data).Results45 of 51 studies included in this review reported maximal RPE values following exercise and ranged from 10.4–20 (6−20 Borg RPE) or 0.9–10 (CR10) indicating “very light” or “very weak” to “maximal” exertions. The 6−20 Borg and CR10 scales were mainly used to assess cardiovascular and muscular exertion, respectively. The scales were used mostly to estimate fatigue levels (n = 45), and to a lesser extent to produce a specific exercise intensity (n = 5) and as the criterion for exercise termination (n = 1). In general, there was no significant association between RPE and postural control changes across studies.ConclusionThe broad range of RPE values and weak correlations may suggest that various fatigue levels can lead to postural control changes. However, one should be careful in comparing the extent of fatigue from RPE values and its potential effect on postural control in the light of many confounding factors.     

Reproducibility of the Balance Evaluation Systems Test (BESTest) and the Mini-BESTest in school-aged children

This study evaluated the intra-rater, inter-rater and test-retest reproducibility of the Full-BESTest and Mini-BESTest when assessing postural control in children. Thirty-four children aged 7–17 years participated in intra-rater and inter-rater evaluation, and 22 children repeated assessment six weeks later for evaluation of test-retest reliability. Postural control was assessed using the Full Balance Evaluation Systems Test (Full-BESTest) and the short-form Mini-BESTest. Intra-rater, inter-rater and test-retest reproducibility were examined using video assessment. Test-retest reproducibility was also assessed in real-time. Reproducibility was examined by agreement and reliability statistics. Agreement was calculated using percentage of agreement, Limits of Agreement and Smallest Detectable Change. Reliability was calculated using Intra-class Correlation Coefficients. Results showed that the reliability of Total Scores was excellent for the Full-BESTest for all conditions (all ICCs > 0.82), whereas the Mini-BESTest ranged from fair to excellent (ICC = 0.56–0.86). Percentage of Domain Scores with good-excellent reliability (ICCs > 0.60) was slightly higher for the Full-BESTest (66%) compared to the Mini-BESTest (59%). Smallest Detectable Change scores were good to excellent for the Full-BESTest (2%–6%) and for the Mini-BESTest (5%–10%) relative to total test scores. Both the Full-BESTest and Mini-BESTest can discriminate postural control abilities within and between days in school-aged children. The Full-BESTest has slightly better reproducibility and a broader range of items, which could be the most useful version for treatment planning. We propose minor modifications to improve reproducibility for children, and indicate the modified version by the title Kids-BESTest. Future psychometric research is recommended for specific paediatric clinical populations.