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.     

Accuracy of passive ankle joint positioning during quiet stance in young and elderly subjects

Age-related postural deficits elicit compensatory mechanisms such as ankle dorsiflexion in the elderly. To gain further insight into this problem, the ability to match an ankle angle during quiet stance was studied in 12 elderly and 12 young subjects. Following an initial single limb angular perturbation presented in the ±4° range, a subject had to return a tilt platform to level, as determined by the nonperturbed limb. Elderly subjects exhibited significant positive (0.9°) over-shoot of the level position, in contrast to young subjects who matched ankle angle with a mean error of −0.1°. The elderly group also exhibited an increase in positioning error for angular displacements in the range between −1 and +1°. The results document age-related postural changes in ankle positioning which might affect postural stability in older adults.     

In vivo kinematics of functional ankle instability patients during the stance phase of walking

BackgroundPrevious studies showed functional ankle instability (FAI) patients have morphological ligamentous abnormality, despite having no apparent joint laxity.Research questionWhether tibiotalar and subtalar joints hypermobility exists in FAI patients during stance phase of walking, remains controversial.MethodsTen unilateral FAI patients, ten unilateral lateral ankle sprain (LAS) copers and ten healthy controls were included. A dual fluoroscopy imaging system was utilized to capture the fluoroscopic images of tibiotalar and subtalar joint during the stance phase of walking. Kinematic data from six degrees of freedom were calculated utilizing a solid modeling software. The range of motion and joint excursions about six degrees of freedom were compared among the three groups. The correlations between range of motion and Cumberland Ankle Instability Tool (CAIT) scores were assessed utilizing the Spearman’s correlation coefficient (r).ResultsDuring the stance phase, the FAI patients and LAS copers showed larger tibiotalar anterior/posterior translation than the healthy controls (FAI patients, p = .013; LAS copers, p = .002). The FAI patients also showed significantly larger lateral/medial translation (p = .035) and inversion/eversion rotation (p = .003) of subtalar joints than healthy controls. By contrast, the subtalar joints of the LAS copers were not different from those of the healthy controls in the lateral/medial translation (p = .459) and inversion/eversion rotation (p = .091). CAIT scores were negatively correlated with range of motion.SignificanceDuring the stance phase of walking, FAI patients showed significantly larger hypermobility of subtalar joints than healthy controls, contrary to the LAS copers. These findings justify the utilization of dual fluoroscopy imaging system to detect joint hypermobility in FAI patients. Treatment for FAI patients may require stabilization of the subtalar joint.     

Slip-related muscle activation patterns in the stance leg during walking

Falls precipitated by slipping are a serious public health concern especially in the elderly. Muscular responses generated during slipping have not been investigated during gait on contaminated floors. This study compared slip-related muscular responses (reactive and proactive) in young and older adults and examined if characteristics of muscular activation patterns during normal gait impact slip severity on contaminated floors. Electromyographic recordings were made from the major shank and thigh muscles in the stance leg of 11 young and nine older adults. Three experimental conditions were included: (1) known dry floors (baseline), (2) unexpected contaminated floor, (3) alert dry (subjects uncertain of the floor's contaminant condition). Muscular responses to unexpected slips, similar in both age groups, included the activation of the Medial Hamstring (175 ms) followed by the onset of the Vastus Lateralis (240 ms). The power and duration of responses were scaled to slip severity. The Vastus Lateralis latency was delayed in severe slips. When experiencing a severe slip, young adults demonstrated a longer, more powerful response compared to older adults. Subjects who normally walk with greater ankle muscle co-contraction were predisposed to experience less severe slips when encountering an unexpected slippery floor. Finally, anticipation of a slippery surface resulted in more powerful muscular activity and muscle co-contraction at the ankle and knee compared to baseline gait, as well as earlier onsets and longer durations in the posterior muscles’ activation. These findings may provide a greater understanding of the higher incidence of falls in the elderly.     

Disrupted somatosensory input alters postural control strategies during the Star Excursion Balance Test (SEBT) in healthy people

BackgroundChronic adaptations, including persistent sensorimotor deficits, remain in individuals with a history of ankle instability, resulting in altered postural control strategies during functional tasks such as gait, running, or landing. However, we do not know the contribution of the altered somatosensory input on postural control strategies during a dynamic balance task such as the Star Excursion Balance Test (SEBT).Research questionThe purpose of this study was to characterize postural control strategies with and without disrupted somatosensory input during a dynamic balance task in people without chronic ankle sprain.MethodsThis study was a crossover study design. Twenty healthy young adults (10 men, 10 women; age = 23.9 ± 3.0 years, height = 174.2 ± 7.4 cm, mass = 71.2 ± 16.7 kg) performed the posteromedial reach test during the SEBT while standing on the ground and on foam. We measured the maximum reach distance (MRD); joint angles of the ankle, knee, hip, and trunk in the sagittal, frontal, and transverse planes; and position and displacement of the center of mass (COM) and center of pressure (COP) during the posteromedial reach task.ResultsThe MRD was shorter when standing on the foam than on the ground (p < 0.001). There was a condition by phase interaction for ankle dorsiflexion; tibia internal rotation; and trunk flexion (p < 0.001; p = 0.03; p = 0.01, respectively). The COM and COP were positioned more laterally on the foam (p < 0.001). The COM and COP anterior-posterior displacements were more anterior during the foam condition (p = 0.017).SignificanceBy using a foam pad to disrupt somatosensory information, participants demonstrated altered strategies to control the joint kinematics, COM, and COP, as a function of posteromedial distance. Ankle and trunk movement strategies may influence the posteromedial reach distance. This model may simulate changes that occur with chronic ankle instability.     

Age-related changes in perception of support surface inclination during quiet stance

The ability to detect that a support surface is level, based upon individual concept of verticality and normal ankle angle during quiet stance, was studied in 11 elderly and 11 young subjects. In response to initial displacement of the tilt platform within a ± 4° range, subjects returned their support surface to level using a hand-held control switch. All sensory inputs regarding the actual platform position were available except direct visual feedback. The task was performed both with eyes open and eyes closed, with both feet on the platform. Elderly subjects exhibited a positive 0.9° shift of the subjective level compared with absolute level, in contrast to young subjects whose subjective level differed from absolute level by not more than 0.25°. There were no significant within-group differences between the eyes open and eyes closed conditions; however, positive shift of the subjective level persisted in the elderly group. The observed shift might be related to a compensatory strategy for overcoming the age-related decline in postural stability in old adults.     

Transient characteristics of body sway during single-leg stance in athletes with a history of ankle sprain

BackgroundThe role of the measurements of postural stability in the context of screening for ankle sprain risk is still equivocal. Transient characteristics of body sway have been suggested as an alternative or an improvement to traditional whole-trial analyses.Research questionAre transient characteristics of body sway sensitive to the history of ankle sprain?.MethodsThe assessment of 30-s single-leg body sway was performed on a group of 93 athletes from basketball, soccer, tennis and running who reported at least 1 ankle sprain in the last 12 months, while a group of 244 athletes from the same disciplines served as a control group without an ankle sprain reported for the same time period. We considered the mean center-of-pressure (CoP) velocity, CoP amplitude and CoP frequency. In addition to traditional whole-trial variables, we calculated the relative differences between the 1 st and the 2nd (DIF_21) and 1 st and 3rd (DIF_31) 10-s time intervals within the whole trial.ResultsThe indexes of transient characteristics of body sway (i.e., the DIF_21 and DIF_31) were in trivial or weak correlations with whole-trial variables (all r ≤ 0.29). Athletes with ankle sprain history exhibited smaller CoP ML velocity (p = 0.002) and larger CoP ML frequency (p = 0.001). In the injured group, the injured leg exhibited lower total and medial-lateral (ML) CoP velocity (p = 0.005−0.040), as well as lower CoP ML amplitude (p = 0.002) and higher CoP ML frequency (p = 0.010). The transient characteristics of body sway (DIF_21 and DIF_31) were very similar between the groups and between the injured and uninjured legs.SignificanceTransient characteristics of body sway do not appear to differentiate the athletes with and without a history of ankle sprain. Further research is needed to confirm if the transient characteristics of body sway could be used for detection of risk of falls in older adults or assessment of athletic performance.     

Lateral ankle sprain alters postural control in bipedal stance: Part 2 sensorial and mechanical effects induced by wearing an ankle orthosis

To investigate the effects induced by wearing an orthosis during the rehabilitation process, 23 ankle sprain patients (degrees I and II) were evaluated in three conditions (reference, with an elastic compression stocking and with an orthosis), 14 h, 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 stability was enhanced during unilateral orthosis wear, explained by a bilateral effect involving both feet. Wearing a compression stocking induced comparably mild intermediate effects compared with the effects observed with the orthosis. These effects were constant throughout the next month. Following lateral ankle sprain, wearing an orthosis allows patients to improve postural function a few hours after the injury to 1 month later. Only cutaneous pressure intervening without mechanical maintenance induced mild effects, indicating that orthosis effects on postural control could partly result from its sensorial stimulation. It, therefore, seems relevant to prescribe orthosis wear for at least 1 month.     

Brain and muscle activation patterns during postural control affect static postural control

BackgroundPrevious studies have reported existence of coordinated brain and muscle activity patterns that affect postural control. However, differences in these activity patterns that affect postural control are still unclear. The purpose of this study was to clarify brain and muscle activity pattern affecting postural control.Research questionDoes the difference in brain and muscle activity patterns during postural control affect postural control ability?MethodNineteen healthy men (mean age: 24.8 ± 4.1 years, height: 171.8 ± 5.5 cm, and weight: 63.5 ± 12.5 kg) performed a postural control task on a balance board, and their brain and muscle activities and body sway during the task were measured using functional near-infrared spectroscopy, surface electromyography, and three-dimensional accelerometry. Hierarchical cluster analysis was conducted to extract subgroups based on brain and muscle activities and postural control, and correlation analysis was performed to investigate the relationship between brain activity, muscle activity, and postural control.ResultsTwo subgroups were found. Subgroup 1 (n = 9) showed higher brain activity in the supplementary motor area (p = 0.04), primary motor cortex (p = 0.04) and stable postural control in the mediolateral (p < 0.01) planes, and subgroup 2 (n = 10) showed higher muscle activity in the tibialis anterior (p < 0.01), a higher shank muscles co-contraction (p = 0.02) and unstable postural control. Furthermore, the supplementary motor area activity is negatively correlated with body sway of mediolateral plane (r = −0.51, p = 0.02), and tibialis anterior activity is positively correlated with body sway on the mediolateral plane (r = 0.62, p = 0.004).SignificanceHigher brain activity in motor-related areas, lower activity in the lower limb muscles and lower co-contraction of shank muscles were observed in stable postural control. These results will facilitate the planning of new rehabilitation methods for improving postural control ability.     

Biomechanical analysis of single-leg stance using a textured balance board compared to a smooth balance board and the floor: A cross-sectional study

BackgroundPrevious research showed that standing on textured surfaces can improve postural control by adapting somatosensory inputs from the plantar foot. The additional stimulation of plantar cutaneous mechanoreceptors by a textured surface during single-leg stance on a balance board may increase afferent information to the central nervous system to accelerate muscular responses and to enhance their accuracy. The additional impact of textured surface during single-leg stance on a balance board on postural control and muscle activity is unknown.Research questionTo investigate the differences of a) postural control during single-leg stance on a textured balance board compared to a smooth balance board and b) activity of lower extremity muscles during single-leg stance on a textured balance board compared to a smooth balance board and the floor.MethodsTwenty-six healthy adults (12 females, 14 males; mean age = 25.4 years) were asked to balance on their randomly assigned left or right leg on a force plate (floor; stable condition), a textured balance board and a smooth balance board (unstable conditions). Center of pressure (CoP) displacements (force plate, Bertec, 1000 Hz) and electromyographic activity (EMG) of eight leg muscles were measured and compared between conditions, respectively.ResultsNeither CoP-displacements, nor EMG activities differed significantly between the textured and the smooth balance board (p > 0.05). Significantly higher muscle activities (p < 0.05) were observed using the balance boards compared to the floor.SignificanceSingle-leg stance using a textured balance board seems not to lead to reduced CoP-displacements compared to a smooth balance board. Muscle activation is significantly increased in both balance board conditions compared to the floor, however, it is not different when both balance board surfaces are compared. It could not be recommended to use a textured balance board for altering muscle activity and improving postural control during single-leg stance in favor of a smooth textured balance board.     

Neuromuscular control of the ankle during pre-landing in athletes with chronic ankle instability: Insights from statistical parametric mapping and muscle co-contraction analysis

ObjectiveThe present study aimed to compare the neuromuscular control of the muscles around the ankle between athletes with CAI and without history of any ankle sprain (Non-CAI) by using statistic parametric mapping (SPM) and co-contraction analyses.DesignCross-sectional study; Setting: Laboratory; Participants: 40 athletes (20 CAI, 20 Non-CAI) were pair-matched for age and gender.Main outcome measuresNeuromuscular control was examined using surface electromyography (EMG) amplitude and muscle co-contraction 200 ms before foot-contact with the ground during a jump-landing task.ResultsThe EMG amplitude of tibialis anterior, peroneus longus, and gastrocnemius medialis were analyzed using statistic parametric mapping. The CAI group exhibited decreased EMG amplitude of peroneus longus during preparation for foot-contact. There were no significant co-contraction differences between groups.ConclusionsOur findings demonstrate that SPM combined with the co-contraction provides a comprehensive EMG analysis to detect the differences of neuromuscular control between athletes with and without chronic ankle instability. Additionally, this finding indicates that CAI contributed to altered neuromuscular control during the pre-landing phase, which may contribute to re-injury mechanisms.     

The effect of trunk muscle fatigue on postural control of upright stance: A systematic review

BackgroundFatigability and postural control deficits are both serious concerns in a variety of chronic musculoskeletal conditions. Research has shown that muscle fatigue may adversely affect postural control. This is while the evidence on the relevance of fatigue to postural control has never been summarized nor critically appraised.Research questionIs there sufficient and strong enough evidence to accept trunk muscle fatigue as a contributing factor to postural control alterations during upright standing posture?.MethodsEMBASE, Scopus, ELSEVIER, PubMed, ProQuest, Google scholar and reference lists of the relevant articles were searched through April 2018. Studies having investigated the trunk muscle fatigue effect on postural control in asymptomatic individuals were included in the study. Only those studies having assessed postural control in terms of center of pressure driven variables were included.ResultsTwelve studies (218 asymptomatic participants) matched the inclusion criteria of this systematic review. Their results supported the hypothesis that fatigue has a significant effect on postural control in terms of the time domain variables. Sway velocity was consistently found to be affected by fatigue. The results were inconsistent in the frequency domain. The only study on the structural dynamics of center of pressure displacements also confirmed such a relationship.SignificanceThe present review indicates that postural control is altered in asymptomatic individuals following trunk muscle fatigue. This may suggest that trunk muscle endurance training is crucial to address postural impairment in chronic spine musculoskeletal conditions.     

The effect of sensory-targeted ankle rehabilitation strategies on single-leg center of pressure elements in those with chronic ankle instability: A randomized clinical trial

Objectives

To determine the effects of sensory-targeted ankle rehabilitation strategies on laboratory-oriented measures of single-leg balance in those with chronic ankle instability.

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.     

Ankle muscle activation during the limits of stability test in subjects with chronic ankle instability

ObjectiveTo study postural control and muscle activity during the limit of stability test (LOS) in subjects with chronic ankle instability.DesignObservational study.SettingUniversity laboratory.Participants10 healthy subjects were included in the control group and 10 subjects in the CAI group (age between 18 and 30 years, with history of the multiple ankle “giving way” episodes in the last six months and score ≤24 in the Cumberland Ankle Instability Tool).Main outcome measuresA computerized dynamic posturography equipment was used for assessing the LOS. The electromyography activity of tibialis anterior (TA), soleus (SOL), medial gastrocnemius (MG) and peroneus longus (PL) was registered.ResultsSubjects with CAI had a greater activation in TA to forward (p < .01), forward affected (p = .001), backward affected (p = .007) and backward directions (p < .01); in PL to forward affected (p < .01) and affected directions (p = .001); in MG to forward (p = .023) and affected directions (p < .01) and in SOL to the affected direction (p = .009). We observed restricted excursions and less directional control in subjects with CAI.ConclusionsSubjects with CAI exhibited poorer ability to move their center of gravity within stability limits. In addition, they have an altered ankle muscle activity during LOS test toward the affected ankle joint.     

Balance failure in single limb stance due to ankle sprain injury: An analysis of center of pressure using the fractal dimension method

Instrumented postural control analysis plays an important role in evaluating the effects of injury on dynamic stability during balance tasks, and is often conveyed with measures based on the displacement of the center-of-pressure (COP) assessed with a force platform. However, the desired outcome of the task is frequently characterized by a loss of dynamic stability, secondary to injury. Typically, these failed trials are discarded during research investigations, with the potential loss of informative data pertaining to task success. The novelty of the present study is that COP characteristics of failed trials in injured participants are compared to successful trial data in another injured group, and a control group of participants, using the fractal dimension (FD) method. Three groups of participants attempted a task of eyes closed single limb stance (SLS): twenty-nine participants with acute ankle sprain successfully completed the task on their non-injured limb (successful injury group); twenty eight participants with acute ankle sprain failed their attempt on their injured limb (failed injury group); sixteen participants with no current injury successfully completed the task on their non-dominant limb (successful non-injured group). Between trial analyses of these groups revealed significant differences in COP trajectory FD (successful injury group: 1.58 ± 0.06; failed injury group: 1.54 ± 0.07; successful non-injured group: 1.64 ± 0.06) with a large effect size (0.27). These findings demonstrate that successful eyes-closed SLS is characterized by a larger FD of the COP path when compared to failed trials, and that injury causes a decrease in COP path FD.     

Patellar bracing affects sEMG activity of leg and thigh muscles during stance phase in patellofemoral pain syndrome

BackgroundDecreases in patellofemoral pain symptoms with bracing treatment have been established; but, the mechanisms remain unclear. The purpose of this study was to determine the immediate and long-term effects of the patellar bracing on electromyography (EMG) activity of the Vastus Medialis (VM) and Lateralis (VL), Rectus Femoris, lateral Gastrocnemius, Biceps Femoris and Semitendinosus (ST) muscles during level walking.Methods12 eligible women aged 20–30 years with diagnosis of patellofemoral pain participated in the before and after study. Intervention consisted of 8 weeks of patellar bracing. First, patients were tested without brace, then with a brace, and finally eight weeks later without a brace. Surface EMG activation of the selected muscles during level walking was recorded.ResultsAfter eight weeks of patellar bracing, EMG activity of VM muscle was significantly higher when compared to first session without brace (p = 0.011) at mid-stance sub-phase. Additionally, EMG activity of ST muscle during first session with brace was significantly lower when compared to first session without brace at mid-stance sub-phase (without brace) (p = 0.012). EMG activity of VM muscle after eight weeks of patellar bracing was significantly higher than the first session without brace at late stance and preswing sub-phase (p = 0.013).ConclusionLong-term wearing of patellar bracing increases EMG activity of VM during mid-stance and late stance and preswing sub-phases of gait and immediate effect of patellar brace is decrease of EMG activity of ST muscle during mid-stance.     

Relationship of chronic ankle instability to muscle activation patterns during the transition from double-leg to single-leg stance

BACKGROUND: Impaired muscle activation may predispose subjects to develop chronic ankle instability. It has been suggested that impairments are found not only in structures around the injured ankle but also around the more proximal joint complexes. HYPOTHESIS: Subjects with chronic ankle instability were expected to show later onset times for lower limb and trunk muscle activation when compared with control subjects. They were expected to show less variability in muscle activation patterns compared with the control group. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty control subjects and 10 subjects with chronic ankle instability participated in the study. The onset of muscle activity of 14 muscles of the lower limb and trunk was measured during the transition from a double-leg stance position to a single-leg stance position in eyes-open and eyes-closed test conditions. RESULTS: Subjects with chronic ankle instability showed significantly later onset times for the ankle, hip, and hamstring muscles compared with control subjects. They used a similar muscle activation pattern in both test conditions, whereas control subjects adjusted their activation pattern according to the condition. CONCLUSIONS: Differences in muscle activation patterns between subjects with chronic ankle instability and control subjects occur not only around the ankle but also around other joints. Subjects with chronic ankle instability show less variability in muscle activation patterns between test conditions. CLINICAL RELEVANCE: Knowledge of muscle activation patterns in the whole lower limb and trunk in noninjured subjects and the differences found in chronic ankle instability subjects broadens the physical therapy approach to the treatment of chronic ankle instability.     

Acute effects of ankle plantar flexor force-matching exercises on postural strategy during single leg standing in healthy adults

BackgroundAnkle plantar flexor force steadiness, assessed by measuring the fluctuation of the force around the submaximal target torque, has been associated with postural stability.Research questionTo investigate whether a force-matching exercise, where submaximal steady torque is maintained at the target torque, can modulate postural strategy immediately.MethodsTwenty-eight healthy young adults performed ankle plantar flexor force-matching exercises at target torques of 5%, 20%, and 50% of maximum voluntary contraction (MVC), in a randomized crossover trial. Participants with their ankle in a neutral position were instructed to maintain isometric contraction at each target torque, as measured by a dynamometer, for 20 s with 3 sets of 5 contractions. Before and after the force-matching exercises, the anterior-posterior velocities and standard deviation of the center of pressure (COP) on the stable platform and the tilt angle of the unstable platform during 20-seconds single-leg standing were measured. The velocities and standard deviations of the COP and tilt angle before and after the exercises were compared using paired t-tests.ResultsThe tilt angle velocity of an unstable platform significantly decreased after the force-matching exercise at a target torque of 5% MVC (p = 0.029), whereas it was unchanged after the exercises at target torques of 20% and 50% MVC. The standard deviations of the tilt angle of unstable platform test did not change significantly after any exercise. Furthermore, no significant differences were observed in the COP velocities or standard deviations on the stable platform test after any exercise.SignificanceOur findings suggest that repeated exertion training at low-intensity contractions can affect postural stability in an unstable condition. Particularly, force-matching exercise at very low-intensity torque, such as 5% of MVC, may be an effective method to improve postural control in the unstable condition, but not in a stable condition.