Center of pressure trajectory during gait: A comparison of four foot positions

Knowledge of the center of pressure (COP) trajectory during stance can elucidate possible foot pathology, provide comparative effectiveness of foot orthotics, and allow for appropriate calculation of balance control and joint kinetics during gait. Therefore, the goal of this study was to investigate the COP movement when walking at self-selected speeds with plantigrade, equinus, inverted, and everted foot positions. A total of 13 healthy subjects were asked to walk barefoot across an 8-m walkway with embedded force plates. The COP was computed for each stance limb using the ground reaction forces and moments collected from three force plates. Results demonstrated that the COP excursion was 83% of the foot length and 27% of the foot width in the anterior–posterior and medial lateral directions for plantigrade walking, respectively. Regression equations explained 94% and 44% of the anterior–posterior and medial–lateral COP variability during plantigrade walking, respectively. While the range of motion and COP velocity were similar for inverted and everted walking, the COP remained on the lateral and medial aspects of the foot for these two walking conditions, respectively. A reduced anterior–posterior COP range of motion and velocity were demonstrated during equinus walking. Ankle joint motion in the frontal and sagittal planes supported this COP movement, with increased inversion and plantar flexion demonstrated during inverted and equinus conditions, respectively. Results from this study demonstrated the COP kinematics during simulated pathological gait conditions, with the COP trajectory providing an additional tool for the evaluation of patients with pathology.     

Center of pressure trajectory during gait: A comparison of four foot positions

Knowledge of the center of pressure (COP) trajectory during stance can elucidate possible foot pathology, provide comparative effectiveness of foot orthotics, and allow for appropriate calculation of balance control and joint kinetics during gait. Therefore, the goal of this study was to investigate the COP movement when walking at self-selected speeds with plantigrade, equinus, inverted, and everted foot positions. A total of 13 healthy subjects were asked to walk barefoot across an 8-m walkway with embedded force plates. The COP was computed for each stance limb using the ground reaction forces and moments collected from three force plates. Results demonstrated that the COP excursion was 83% of the foot length and 27% of the foot width in the anterior–posterior and medial lateral directions for plantigrade walking, respectively. Regression equations explained 94% and 44% of the anterior–posterior and medial–lateral COP variability during plantigrade walking, respectively. While the range of motion and COP velocity were similar for inverted and everted walking, the COP remained on the lateral and medial aspects of the foot for these two walking conditions, respectively. A reduced anterior–posterior COP range of motion and velocity were demonstrated during equinus walking. Ankle joint motion in the frontal and sagittal planes supported this COP movement, with increased inversion and plantar flexion demonstrated during inverted and equinus conditions, respectively. Results from this study demonstrated the COP kinematics during simulated pathological gait conditions, with the COP trajectory providing an additional tool for the evaluation of patients with pathology.     

Improvements in balance control in individuals with PCS detected following vestibular training: A case study

Concussed individuals have been found to experience balance deficits in the anterior-posterior (AP) direction as indicated by greater Center of Pressure (COP) displacement and velocity. One possible reason for this change in balance control could be due to damage to the lateral vestibulospinal tract which sends signals to control posterior muscles, specifically ankle extensors leading to compensatory torques about the ankle. The purpose of the study was to quantify balance assessments in individuals experiencing persistent post-concussion symptoms (PCS) to determine balance control changes following a vestibular training intervention. Participants (N = 6, >26 days symptomatic), were tested during their first appointment with a registered physiotherapist (PT) and during each follow up appointment. Participants were prescribed balance, visual, and neck strengthening exercises by the PT that were to be completed daily between bi-weekly appointments. Balance assessments were quantified using a Nintendo Wii board to record ground reaction forces. Participants completed 4 balance assessments: 1) Romberg stance eyes open (REO); 2) Romberg stance eyes closed (REC); 3) single leg stance eyes open (SEO); and 4) single leg stance eyes closed (SEC). The balance assessments were conducted on both a firm and compliant surfaces. Significant improvements in balance control were noted in ML/AP displacement and velocity of COP for both SEC and Foam REC conditions, with additional improvements in AP velocity of COP for Foam REC and in ML displacement of COP during Foam SEC. Overall, findings indicate that objectively quantifying balance changes for individuals experiencing persistent PCS allows for a more sensitive measure of balance and detects changes unrecognizable to the naked eye.     

Effects of assistive devices on postural control following a balance disturbance along the anterior-posterior direction

BackgroundAssistive devices provide balance and stability to those who require a greater base of support, especially during ambulation or in tasks essential to functional daily living. In ambulatory assistive device use, center of pressure (COP) movement as one of the measurements of postural control is a factor when assessing fall risk, with an overall goal of maintaining postural equilibrium. There is a lack of research on assistive devices, such as walkers, regarding measurable outcome variables related to fall risk. The purpose of this study was to determine how much the postural control in single limb stance during a balance perturbance is affected by utilizing three different walker types designed to promote stability: the standard walker, the front-wheeled walker with straight wheels and the front-wheeled walker with caster wheels.Research questionIs postural sway control in single limb stance during a balance perturbance affected by walker type?MethodsTwenty-three healthy adults participated and gave consent. The NeuroCom® SMART EquiTest® system was utilized to simulate forward falls. Subjects stood on the system’s force plate, which was tipped backwards quickly, forcing subjects to attempt to maintain balance. Each participant experienced 18 simulated perturbations, during which they were asked to maintain balance while using one of three walkers in single-limb stance. Each trial was completed using random assignment of three different walker types. Leg dominance of the stance leg was also randomized for each trial.ResultsThe type of walker and the leg dominance in the standing limb significantly affected postural control in a balance perturbance in the A-P direction. The walker type significantly affected the COP maximum displacement in anterior-posterior (AP) direction. However, the leg dominance significantly affected COP maximum displacement in AP and medio-lateral (ML) directions and COP velocity in AP direction.SignificanceThe findings suggest that when fully grounded, a standard walker is more stable than the front-wheeled walker. However, this does not indicate that the standard walker is more stable than other types of walkers when it is being picked up and moved forward during normal use.     

Reliability of center of pressure measures within and between sessions in individuals post-stroke and healthy controls

BackgroundKnowing the reliability of the center of pressure (COP) is important for interpreting balance deficits post-stroke, especially when the balance deficits can necessitate the use of short duration trials. The novel aspect of this reliability study was to examine the center of pressure measures using two adjacent force platforms between and within sessions in stroke and controls. After stroke, it is important to understand the contribution of the paretic and non-paretic leg to the motor control of standing balance. Because there is a considerable body of knowledge on COP reliability on a single platform, we chose to examine reliability using two adjacent platforms which has not been examined previously in stroke.MethodsTwenty participants post-stroke and 22 controls performed an arm raise, load drop and quiet stance balance task while standing on two adjacent force platforms, on two separate days. Intraclass correlations coefficient (ICC_2,1) and percentage standard error of measurement (SEM%) were calculated for COP velocity, ellipse area, anterior–posterior (AP) displacement, and medial–lateral (ML) displacement.ResultsBetween sessions, COP velocity was the most reliable with high ICCs and low SEM% across groups and tasks and ellipse area was less reliable with low ICCs across groups and tasks. COP measures were less reliable during the arm raise than load drop post-stroke. Within session reliability was high for COP velocity and ML displacement requiring no more than six trials across tasks.ConclusionsThe COP velocity was the most reliable measure with high ICCs between sessions and the high reliability was achieved with fewer trials in both groups in a single session.     

Alterations in medial-lateral postural control after anterior cruciate ligament reconstruction during stair use

BackgroundDynamic postural control during everyday tasks is poorly understood in people following anterior cruciate ligament reconstruction (ACLR). Understanding dynamic postural control can provide insight into potentially modifiable impairments in people following ACLR who are at increased risk for second ACL injury and/or knee osteoarthritis.Research questionDetermine whether measures indicative of dynamic postural control differ between individuals with and without ACLR during stair ascent and descent. Methods: Seventeen individuals with ACLR (>1 yr post-surgery) and 16 age and sex-matched healthy controls participated. Centre of pressure (COP) measures included: i) COP excursion, ii) COP velocity, and iii) dynamic time-toboundary (TTB). Mixed linear models were used to compare COP measures for the ACLR leg, non-ACLR leg, and healthy controls during stair ascent and stair descent.ResultsThere were no statistically significant differences observed during stair ascent (all p > 0.05). Several statistical differences were found during stair descent for individual with ACLR, but not between those with ACLR and healthy controls. The ACLR leg had higher medial-lateral COP excursion (mean difference 1.06 cm, [95 %CI 0.08–2.06 cm], p = 0.036; effect size = 0.38) compared to the non-ACLR leg during stair descent. In addition, the ACLR leg had a lower medial-lateral TTB (mean difference −13 ms [95 %CI −38 to 2 ms], p = 0.005; effect size = 0.49) and medial-lateral TTB normalized to stance time (mean difference −5.8 % [95 %CI −10.3 to 1.3 %], p = 0.012; effect size = 0.80) compared to the non-ACLR leg during stair descent. No statistical differences were observed for anterior-posterior measures during stair descent (all p > 0.05). Significance: Taken together, findings indicate that there are small to large differences in medial-lateral postural control in the ACLR leg compared to the non-ACLR leg during stair descent. Further work is required to understand clinical implication of these novel observations.     

Spatial postural control alterations with chronic ankle instability

Postural control deficits have been identified among individuals with chronic ankle instability (CAI) compared to healthy controls. Although deficits in static balance have previously been reported using center of pressure (COP) and, more recently, time to boundary (TTB) measures, the underlying mechanism behind these deficits warrants further investigation. It is unclear if there are differences in the spatial distribution of COP and TTB minima data points under the foot. Our purpose was to determine if there are differences in the location of the distribution of the COP and the TTB minima data points between groups with and without CAI. Fifty healthy and 61 CAI subjects participated in this case-control study. The subjects performed three successful 10-s trials of quiet single limb stance on a force plate with eyes-open and -closed conditions. Results showed that during eyes-open trials, the CAI group exhibited more COP and TTB minima data points on the anterolateral aspect of the foot compared to controls. With eyes-closed single limb balance, the CAI group demonstrated significantly more COP and TTB minima data points anterior to the horizontal midline of the foot compared to controls. Overall, the CAI group showed a greater anterior displacement of COP and TTB minima during single limb static stance compared to controls. This alteration may result from the CAI subjects adopting a more dorsiflexed position in an effort to keep the ankle in a more stable, closed pack position and limiting the available degrees of freedom in the distal lower extremity.     

Balance is impaired in symptomatic ankle osteoarthritis: A cross-sectional study

BackgroundAnkle osteoarthritis (OA) is associated with several physical impairments but investigations into balance impairments in this population are limited. Understanding balance impairments in ankle OA may help inform the management of this condition.Research questionDoes balance overall performance differ between individuals with symptomatic radiographic ankle OA, asymptomatic radiographic ankle OA and healthy controls? Are there any differences in mediolateral or anteroposterior balance, or confidence to perform balance tasks between these groups?MethodsNinety-six volunteers (31 symptomatic radiographic ankle OA, 41 asymptomatic radiographic ankle OA and 24 healthy controls) completed six static balance tasks: bilateral stance on a firm surface, bilateral stance on foam, and tandem stance, all performed with eyes open and closed. Centre of pressure (COP) data were collected using force plates. Confidence to perform each balance task was collected using an 11-point numerical rating scale.ResultsCompared to controls, participants with symptomatic radiographic ankle OA had greater COP area when standing on a firm surface, foam and in tandem with eyes closed (all p < 0.05) and greater total COP sway in both firm surface and tandem stance conditions (p < 0.04). Participants with symptomatic ankle OA had greater COP area (p < 0.04) and total COP sway (p = 0.01) than those with asymptomatic ankle OA during tandem stance. Total COP sway and area were similar between asymptomatic ankle OA and control participants. Some differences in mediolateral and anteroposterior balance were identified between groups. Individuals with symptomatic ankle OA had lower confidence to perform the tandem stance eyes closed task compared to controls.SignificanceBalance impairments and decreased balance confidence were identified in those with symptomatic radiographic ankle OA compared to asymptomatic individuals with and without radiographic ankle OA. This suggests that balance deficits in ankle OA may be related to symptoms, rather than radiographic evidence of disease.     

Center of pressure during stance and gait in subjects with or without persistent complaints after a lateral ankle sprain

Study aimTo investigate differences in the center of pressure (COP) during gait and single leg stance between subjects with persistent complaints (PC) and without persistent complaints (NPC) after a lateral ankle sprain.Methods44 patients who consulted the general practitioner, 6–12 months prior to inclusion, with a lateral ankle sprain were included for the current study purpose. Using a 7-point Likert scale patients were divided into the PC or NPC group. All subjects filled out an online questionnaire, walked along a walkway and performed a single leg stance, both on the RSscan. Primary outcomes included the COP displacement, range and percentage used in mediolateral and anterioposterior direction.ResultsThere was a trend (p < 0.05) towards a more medially COP trajectory during walking at 34–46% and 83–96% and more anteriorly at 21–31% and 91–100% of the stance phase in the PC group compared to NPC group. Additionally, the COP was more laterally located in the sprained leg compared to the non-sprained leg in the PC group in the loading response phase (p < 0.05). An interaction was found for the percentage of anterior–posterior range used in single leg stance without vision.ConclusionThe COP trajectory discriminates between patients with PC and NPC. This indicates that roll off during gait might play an important role in the recovery of patients after a lateral ankle sprain and could be used to monitor treatment.     

Center of pressure characteristics differ during single leg stance throughout pregnancy and compared to nulligravida individuals

BackgroundFalls are common during pregnancy and present potential for injury to the pregnant individual and the baby.Research questionDo center of pressure characteristics during single leg stance differ between participants during and after pregnancy and nulligravida participants in the presence and absence of visual input?MethodsNineteen pregnant participants completed testing during the second trimester, the third trimester, and 4–6 months post-partum. Matched, nulligravida females completed testing once. All participants performed single leg stance on a force platform on each limb for up to 20 s with eyes open and with eyes closed. Center of pressure characteristics were compared between pregnant and nulligravida females using three separate 2 × 2 mixed way ANOVAs, one for each pregnancy time point (second trimester, third trimester, and post-partum) with Bonferroni correction.ResultsPregnant females demonstrated smaller single leg stance time with eyes closed during the third trimester. During the second and third trimester, pregnant participants demonstrated smaller sway and sway velocity across eyes open and eyes closed conditions. During the third trimester and post-partum, pregnant participants demonstrated greater median frequency of the center of pressure data. Pregnant participants also demonstrated smaller sample entropy in the anteroposterior direction during the second and third trimesters and in the mediolateral direction during the second trimester.SignificanceThe decreased total sway and sway velocity observed during pregnancy may reflect rigidity or a protective strategy during single limb stance. Additionally, center of pressure data were less smooth and more repetitive during pregnancy indicating robust differences in postural control strategies and potentially increased fall risk. Because single limb stance is a component of many activities of daily living, the single limb stance task may have clinical utility for testing or training balance in this population with a goal of decreasing falls.     

Functional fatigue of the hip and ankle musculature cause similar alterations in single leg stance postural control

Isokinetic fatigue protocols have been used to determine the relative importance of lower extremity musculature to the maintenance of balance. However, these protocols are not representative of physical activity, thus the recommendations based on these findings may be inappropriate. Therefore, purpose of this investigation was to use a completely within subjects design to examine the effects of a functional ankle and hip fatigue protocol on postural control during single leg stance. All testing was completed in a health and wellness facility where 18 healthy recreationally active university students (nine female, nine male: 21.2 ± 1.96 years, 72.2 ± 17.8 kg, 170.4 ± 10.12 cm) volunteered to participate. Testing consisted of functionally fatiguing the ankle plantar flexors and dorsiflexors as well as the hip flexors and extensors. Postural control was assessed with two pre- and post-fatigue 20 s trials during single leg stance. Three measures of dynamic balance: the overall, medial/lateral, and anterior/posterior stability index were calculated using the Biodex Stability System at stability level 4. Three separate 2-way repeated measure ANOVAs indicated that fatigue of both the ankle (plantar flexors, dorsiflexors) and hip (flexors, extensors) musculature led to postural control impairments for the medial–lateral stability index (p < 0.01), and anterior–posterior stability index (p < 0.01). However, only ankle fatigue resulted in deficits in the overall stability index were (p < 0.01). Furthermore, neither fatigue protocol impaired single leg stance postural control more than the other (p > 0.05). Our results contradict previous isokinetic fatigue protocol findings, which indicate that proximal musculature fatigue results in greater postural control deficits.     

Relationship between static and dynamic balance tests among elite Australian Footballers.

Research assessing the direct relationship between static and dynamic balance ability of athletes is sparse. The aim of this project was to determine the relationship between a static balance task on a firm surface with a stepping balance task on an unstable surface. Thirty-seven Australian male professional footballers participated in the study. The static test involved maintaining single limb stance on a force platform. The other balance test involved stepping on to a balance mat on top of the force platform and maintaining single limb stance. The centre of pressure was monitored and the maximum excursion in the medial-lateral direction was recorded and used as the balance value. It was found that the magnitude of the maximum centre of pressure excursion was significantly greater (53%) for the stepping balance task. There were significant but low correlations for the centre of pressure excursion values between the two balance tests for the right limb and average of both limbs. There was no significant correlation between the test values for the left limb. Only a small proportion of the variance could be explained by each test: 16% for right limb values, 7% for left limb values and 11% for the average of both limbs. Given the overall weak associations between the two balance test values, it was concluded that performance in the static balance test was not reflective of performance in the dynamic balance test. Attempting to infer dynamic balance ability based on static balance ability should be avoided.     

Aging effects on postural responses to self-imposed balance perturbations

The present study investigated how young and older individuals organize their posture in response to self-induced balance perturbations evoked by oscillatory single limb movements. Eleven old (70.1+/-4.3 years) and nine young (20.1+/-2.4 years) participants performed repeatedly for 5s hip flexion/extension movements using full range of motion and maximum velocity. Two-dimensional joint kinematics (sampling rate: 60Hz), center of pressure (CoP) and EMG activity of tibialis anterior (TA), medial gastrocnemius (MGAS) rectus femoris (RF) and, semitendinosus (ST) in the stance limb were recorded and analysed. Cross-correlation function (CCF) analysis was used to identify the degree of coupling between the swinging limb (SL), center of gravity (CoG) and CoP motions. Old adults significantly limited SL, CoG and CoP range of anterior/posterior (A/P) motion in response to the forceful leg swinging. In the stance limb, significantly lower levels of ankle muscle activity resulted in reduced hip and knee joint excursions and increased ankle instability. By contrast, young performers produced sufficient ankle muscle activity to stabilize the foot to the ground while progressively increasing joint range of motion from the ankle to the hip. Center of pressure and SL movements were strongly correlated in an anti-phase relationship in both age groups. In older adults, however, the relationship between CoG-SL and CoG-CoP movements was neither strong nor synchronous, reflecting a weaker coupling and lack of coordination between component movements. It is concluded that insufficient ankle muscle activity, central integration deficits and increased anxiety to postural threat are important factors implicated for the weaker postural synergies and freezing of degrees of freedom seen in the elderly during performance of single limb oscillations.     

Postural stability during visual-based cognitive and motor dual-tasks after ACLR

ObjectivesDetermine the effect of visual-based motor and cognitive dual tasking on postural stability in those with anterior cruciate ligament reconstruction relative to matched controls.DesignCohort study.MethodsFourteen volunteers with history of anterior crucaite ligament reconstruction were matched with fourteen healthy controls. Participants performed single leg balance tasks under 4 conditions: (1) single leg balance with eyes-open, (2) single leg balance while catching a ball (dual-motor), (3) single leg balance while repeating a string of numbers in reverse order after viewing them (dual-cognitive) and (4) single leg balance with eyes-closed. Participants completed several patient-reported outcomes of knee function. Mixed effects models were used to identify group differences on the center of pressure measures of ellipse area and root-mean-squared excursion (medial–lateral and anterior–posterior). The mixed models included subject pair as a random factor and group (control, anterior cruciate liagement reconstruction), balance condition (eyes-open, eyes-closed, dual-cognitive, and dual-motor), and group*condition as fixed effects. Tukey post-hoc pairwise comparisons were performed for significant interaction and main effects with an α = 0.05.ResultsA significant group by condition interaction was observed for ellipse area and medial–lateral root-mean-squared excursion. The anterior cruciate ligament reconstruction group had higher ellipse area (p = 0.002, d = 0.44) and medial–lateral root-mean-squared excursion (p < 0.001, d = 0.49).ConclusionsPostural stability is greatly impaired under eyes-closed and dual-motor conditions relative to eyes-open. Anterior cruciate ligament reconstructed individuals have greater postural instability during the dual-cognitive condition that may indicate unique neural processing deficits remain following anterior cruciate ligament reconstruction.     

Deficits in time-to-boundary measures of postural control with chronic ankle instability

Our purpose was to examine postural control in single leg stance in subjects with and without unilateral chronic ankle instability (CAI) using traditional center of pressure (COP)-based and time-to-boundary (TTB) measures. Fifteen physically active females with self-reported unilateral chronic ankle instability (CAI) and nine healthy female controls performed three 10-s trials of eyes open single limb quiet standing on a force plate on both their legs. The traditional measures were mean COP velocity, standard deviation of COP, range of COP, and percent of available range utilized. The TTB measures were absolute minimum TTB, mean of the minimum TTB samples, and standard deviation of the minimum TTB samples. All measures were calculated in both the mediolateral (ML) and anteroposterior (AP) directions. A 2x2 group (CAI, control) by side (involved, uninvolved) design was utilized. The CAI group had significantly lower scores for five of the six TTB measures compared to the control group, however only one (AP COP velocity) of the eight traditional measures was different between groups. The TTB measures appear to detect postural control deficits related to CAI that traditional measures do not.     

Quantification and reliability of center of pressure movement during balance tasks of varying difficulty

Postural control is often assessed by quantifying the magnitude of the center of pressure (COP) movement. However, these measures usually focus on the gross amount of movement and ignore the temporal structure of the COP signal. A novel non-linear analysis technique was recently developed to characterize the temporal structure of the COP signal with an output termed the entropic half-life [E(1/2)]. The E(1/2) reflects how much of the previous postural position is used to determine the current postural control strategy (memory effect). The purpose of this study was to quantify the E(1/2) and four COP movement magnitude measurements (medio-lateral and anterior–posterior excursion, path length, 95% ellipse area) for balance tasks increasing in sensory difficulty, as well as the test–retest reliability of each measure. Twenty-seven healthy young adults completed single limb stance tasks varying in sensory difficulty (rigid surface eyes open, rigid surface eyes closed, foam surface eyes open) on two separate occasions. Relative reliability was assessed using an intraclass correlation coefficient (ICC_3,3). Absolute reliability was assessed using the standard error of the measurement (SEM) and the sensitivity of the measurement to true changes was assessed using the minimal detectable change (MDC₉₅). The E(1/2) was found to have excellent reliability for all tasks tested (ICC range 0.82–0.91, SEM range 3.5–14.1 mm, MCD₉₅ range 9.7–39.2 mm). The high reliability of the E(1/2) was comparable to that of movement magnitude measurements. This may be used in order to better understand the underlying motor control system.     

Landing stability in anterior cruciate ligament deficient versus healthy individuals: A motor control approach

ObjectivesTo compare the temporal effectiveness of landing strategies in anterior cruciate ligament deficient (ACLD) versus non-injured participants, when they landed on one leg after running or after a single leg hop.DesignCase control study.SettingLaboratory setting.ParticipantsParticipants were 30 ACLD patients and 30 control subjects.Main outcome measuresTime to stabilise (TTS) was measured using centre of pressure (COP), horizontal (Fy) and vertical (Fz) force velocity on a Kistler forceplate. Kinematic data were collected using a Vicon 512 system with 8 IR cameras. Between group differences were analysed using a two-way ANOVA with post hoc t-tests.ResultsSignificant group differences were found in running speed, hop distance, failed attempts, deceleration, and TTS using COP velocity in both activities.ConclusionsWhen required to stop and balance on their injured leg, ACLD participants selected slower running speeds and less hop distance to succeed from than did controls, and they used different strategies to stabilise upon landing. They also showed a significantly poorer ability to maintain stable stance following deceleration. ACLD individuals who were able to adapt with some success did so by increasing the time available to them and limiting function to within the boundaries they can control effectively.     

Individuals with chronic ankle instability exhibit decreased postural sway while kicking in a single-leg stance

Individuals with chronic ankle instability (CAI) usually experience deficits in balance control, which increase displacement in the body's center of pressure (COP) when they balance on a single leg. Little is known, however, about whether or not these individuals use the strategies of postural adjustment properly, especially during functional tasks that may predispose them to ankle sprain. The aim of this study was to investigate anticipatory (APA) and compensatory (CPA) postural adjustments in individuals with and without CAI as they kick a ball while standing in a single-leg stance with their ankle in neutral and supinated positions. COP displacements were calculated and their magnitudes (range) analyzed during APA and CPA intervals and over the duration of the whole task, represented by the COP area of sway and mean velocity. The CAI group exhibited a significant decrease in CPA and area of sway over the whole task, relative to controls. These results suggest that the decreased balance sway could be caused by the need for further stabilization of the ankle in more unstable postures to prevent recurrent sprain. Our findings could help clinicians to better understand the strategies of postural adjustments in individuals with CAI, and may assist and motivate new investigations into balance control interventions in such individuals, as well as proactively address recurrent ankle sprain conditions.     

Ankle muscle coactivation during gait is decreased immediately after anterior weight shift practice in adults after stroke

Increased ankle muscle coactivation during gait has frequently been observed as an adaptation strategy to compensate for postural instability in adults after stroke. However, it remains unclear whether the muscle coactivation pattern increases or decreases after balance training. The aim of this study was to investigate the immediate effects of balance practice on ankle muscle coactivation during gait in adults after stroke. Standing balance practice performed to shift as much weight anteriorly as possible in 24 participants after stroke. The forward movement distance of the center of pressure (COP) during anterior weight shifting, gait speed, and ankle muscle activities during 10-m walking tests were measured immediately before and after balance practice. Forward movement of the COP during anterior weight shifting and gait speed significantly increased after balance practice. On the paretic side, tibialis anterior muscle activity significantly decreased during the single support and second double support phases, and the coactivation index at the ankle joint during the first double support and single support phases significantly decreased after balance practice. However, there were no significant relationships between the changes in gait speed, forward movement of the COP during anterior weight shifting, and ankle muscle coactivation during the stance phase. These results suggested that ankle muscle coactivation on the paretic side during the stance phase was decreased immediately after short-term anterior weight shift practice, which was not associated with improved gait speed or forward movement of the COP during anterior weight shifting in adults after stroke.     

Between-leg asymmetry in automatic postural responses to stance perturbations in people with Parkinson's disease

BackgroundPeople with Parkinson's disease (PwPD) showed impairments of balance control which can be aggravated by the presence of higher interlateral postural asymmetry caused by a distinct dopaminergic loss in the substantia nigra between cerebral hemispheres.Research questionWe evaluate asymmetries between the more and the less affected leg in PwPD in responses to unanticipated stance perturbations.MethodsSixteen 16 PwPD participated in the experiment that consisted of recovering a stable upright stance, keeping the feet in place, in response to a perturbation caused by a sudden release of a load equivalent to 7 % of the participant's body mass. Anterior displacement and velocity of the center of pressure (CoP), the latency of gastrocnemius medialis muscle (GM) activation onset, rate of GM activation, and normalized magnitude of muscular activation were analyzed.ResultsAnalysis revealed significantly rate (p = 0.04) and magnitude (p = 0.02) higher activation of GM in the less affected limb. No significant effects of the leg were found for GM activation latency or CoP-related variables.SignificanceThere is a higher contribution of the less affected leg in automatic postural responses in PwPD.