Process of dynamic balance recovery after voluntary perturbation: a time-series data analysis of young and older adults.

[Purpose] This study investigated differences in the convergence mode of post-step sway between young and older adults using a step-down task to identify fall causes in older adults and assess consecutive postural adjustments. [Participants and Methods] This study included 15 young and 15 older adults (nine females and six males in each group). The participants stepped down from a standing position to a force platform 10 cm lower and maintained a one-leg standing position. The center-of-pressure total trajectory length was assessed using a force plate and regression equations for time and sway were derived from the associated time-series data for both groups. [Results] An inversely proportional aspect was observed for both groups, with significantly different coefficients and constants. The center-of-pressure total trajectory length per second from foot contact was significantly different between 2-3 s and 4-5 s in the older group but not in the younger group. [Conclusion] The results suggest a difference in the convergence mode of dynamic balance between the two groups, with young adults exhibiting a more rapid balance-sway reduction than older adults. The novel computational approach used in this study may be useful for dynamic balance measurements.

Neuromuscular adaptations to perturbation-based balance training using treadmill belt accelerations do not transfer to an obstacle trip in older people: A cross-over randomised controlled trial.

BACKGROUND: This study examined (i) adaptations in muscle activity following perturbation-based balance training (PBT) using treadmill belt-accelerations or PBT using walkway trips and (ii) whether adaptations during treadmill PBT transfer to a walkway trip. METHODS: Thirty-eight older people (65+ years) undertook two PBT sessions, including 11 treadmill belt-accelerations and 11 walkway trips. Surface electromyography (EMG) was measured bilaterally on the rectus femoris (RF), tibialis anterior (TA), semitendinosus (ST) and gastrocnemius medial head (GM) during the first (T1) and eleventh (T11) perturbations. Adaptations (within-subjects - 1st vs 11th perturbations for treadmill and walkway PBT) and their transfer (between-subjects - 1st walkway trip after treadmill PBT vs 1st walkway trip with no prior training) effects were examined for the EMG parameters. RESULTS: Treadmill PBT reduced post-perturbation peak muscle activation magnitude (left RF, TA, ST, right RF, ST, GM), onset latency (right TA), time to peak (right RF) and co-contraction index (knee muscles) (P < 0.05). Walkway PBT reduced post-trip onset latencies (right TA, ST), peak magnitude (left ST, right GM), time to peak (right RF, ST) and pre-perturbation muscle activity (right TA) (P < 0.05). Those who undertook treadmill PBT were not different to those without prior training during the first walkway trip (P > 0.05). CONCLUSIONS: Both treadmill and walkway PBT induced earlier initiation and peak activation of right limb muscles responsible for the first recovery step. Treadmill PBT also reduced co-contraction of the knee muscles. Adaptations in muscle activity following treadmill PBT did not transfer to a walkway trip.

Comparative Effects of Fatiguing Exercise on Anticipatory and Compensatory Postural Adjustments between Trained and Untrained Individuals.

This study evaluates the effects of general fatiguing exercises on anticipatory postural adjustments (APAs), compensatory postural adjustments (CPAs), and standing stability between 18 individuals with comprehensive training experience (TR) and 18 untrained individuals (UT). Assessments were conducted before and after a 20-min fatiguing exercise using surface electromyography and a force platform during self-initiated perturbation and postural stability tests. Key findings include that, irrespective of fatigue, the APAs onsets in the TrA/IO (p = 0.004), LMF (PRE p = 0.003, POST p < 0.001), and ST (PRE p = 0.001, POST p = 0.006) muscles activated earlier in the TR group than in the UT group. Additionally, the APA co-contraction indices of the TrA/IO-LMF (PRE p = 0.011, POST p = 0.029), TrA/IO-ST (p = 0.014), and LMF-ST (PRE p = 0.002, POST p = 0.005) muscle pairs were higher in the TR group. After fatigue, the UT group significantly increased CPA co-contraction indices for the TrA/IO-LMF (p = 0.035) and LMF-ST (p = 0.005) muscle pairs. This research highlights the importance of comprehensive training in facilitating feedforward control strategies, particularly for individuals facing challenging postural conditions, such as fatigue or disturbances.

Directional-Specific Modulation of Postural Control and Stepping Kinematics in Multidirectional Gait Initiation.

Daily living activities present a diverse array of task and environmental constraints, highlighting the critical role of adapting gait initiation (GI) for an individual's quality of life. This study investigated the effects of GI directions, obstacle negotiation, and leg dominance on anticipatory postural adjustments and stepping kinematics. Fourteen active, young, healthy individuals participated in GI across 4 directions-forward, medial 45°, lateral 45°, and lateral 90°-with variations in obstacle presence and leg dominance. Results revealed a consistent decreasing trend in maximum center of pressure displacement, anticipatory postural adjustment duration, step distance, and swing leg velocity with lateral shifts in GI directions, yet the step duration and swing leg heel trajectory were not affected by GI directions except in lateral 90° GI. Center of pressure displacements were intricately scaled to directional propulsive forces generation, and the stepping kinematics were influenced by the directional modifications in movements. With obstacles, modifications in anticipatory postural adjustment metrics and stepping kinematics reflected the obstacle clearance movements. The dominant leg GI exhibited longer step durations and greater movement variability in medial 45° GI. The current investigation of GI factors expands our existing understanding of GI dynamics and offers valuable insights applicable to fall prevention and gait rehabilitation strategies.

Effects of unilateral and bilateral lower extremity fatigue on static stance and postural adjustments response to the externally initiated perturbation.

The study investigated the effects of unilateral and bilateral lower extremity fatigue on both postural stability and postural adjustments. Fourteen young male subjects performed unilateral and bilateral dynamic lower extremity pedaling exercises with 5 sets of 20 times at 50 % maximum voluntary contraction. Center of pressure (COP) signals were recorded before and after the fatigue exercise. Electromyography activities of six trunk and leg muscles were recorded and analyzed during the anticipatory (APAs) and compensatory (CPAs) postural adjustments. The results showed that both fatiguing exercises caused an increase in COP and larger APAs and CPAs in the rectus femoris and tibialis anterior during externally initiated perturbation. However, the observed indicators showed no clear difference between unilateral and bilateral fatigue. These results validated that when enlarged APAs were not sufficient to resist the external perturbation, the central nervous system increased the strength of CPAs to maintain the stability of the body. These findings provided a perspective on the association between APAs and CPAs, which may apply to the athletic training or rehabilitation on postural control.

Reduction in preparatory brain activity preceding gait initiation in individuals with chronic ankle instability: A movement-related cortical potential study.

Evidence suggests that chronic ankle instability (CAI) is not merely a peripheral musculoskeletal injury but should be recognized as a neurophysiological dysfunction. This reflects a paradigm shift from focusing on peripheral structural changes to emphasizing the central nervous system. However, changes in cortical activity during functional activities remain poorly understood. Thus, this study aimed to compare preparatory brain activity during gait initiation (GI) through movement-related cortical potentials (MRCPs) in individuals with CAI and healthy subjects. The proactive components of MRCPs, including contingent negative variation (CNV) and event-related desynchronization (ERD), were measured using electroencephalography. The primary outcomes were late CNV amplitude, CNV peak amplitude, CNV peak time, and alpha/beta ERD. The results indicated that the late CNV amplitude was significantly lower in the CAI group compared to the healthy group at the Fz and Cz electrodes (P < 0.001). The CAI group also demonstrated lower CNV peak amplitude at the Fz, Cz, and Pz electrodes (P < 0.0025). Additionally, in the CAI group, signals peaked earlier at the Cz electrode (P = 0.002). Furthermore, alpha ERD at Pz was significantly lower in the CAI group than in the healthy group (P = 0.003), suggesting diminished preparatory brain activity during GI in CAI subjects. Recognizing CAI as a condition involving both peripheral and central dysfunctions highlights the importance of a multidisciplinary approach in treatment and rehabilitation. This approach should target brain activity in addition to peripheral structures, potentially leading to improved long-term outcomes for patients.

Predictive posture stabilization before contact with moving objects: equivalence of smooth pursuit tracking and peripheral vision.

Postural stabilization is essential to effectively interact with our environment. Humans preemptively adjust their posture to counteract impending disturbances, such as those encountered during interactions with moving objects, a phenomenon known as anticipatory postural adjustments (APAs). APAs are thought to be influenced by predictive models that incorporate object motion via retinal motion and extraretinal signals. Building on our previous work that examined APAs in relation to the perceived momentum of moving objects, here we explored the impact of object motion within different visual field sectors on the human capacity to anticipate motion and prepare APAs for contact between virtual moving objects and the limb. Participants interacted with objects moving toward them under different gaze conditions. In one condition, participants fixated on either a central point (central fixation) or left-right of the moving object (peripheral fixation), whereas in another, they followed the moving object with smooth pursuit eye movements (SPEMs). We found that APAs had the smallest magnitude in the central fixation condition and that no notable differences in APAs were apparent between the SPEM and peripheral fixation conditions. This suggests that the visual system can accurately perceive motion of objects in peripheral vision for posture stabilization. Using Bayesian model averaging, we also evaluated the contribution of different gaze variables, such as eye velocity and gain (ratio of eye and object velocity) and showed that both eye velocity and gain signals were significant predictors of APAs. Taken together, our study underscores the roles of oculomotor signals in the modulation of APAs.NEW & NOTEWORTHY We show that the human visuomotor system can detect motion in peripheral vision and make anticipatory adjustments to posture before contact with moving objects, just as effectively as when the eye movement system tracks those objects with smooth pursuit eye movements. These findings pave the way for research into how age-induced changes in spatial vision, eye movements, and motion perception could affect the control of limb movements and postural stability during motion-mediated interactions with objects.

Accelerometer approach for anticipatory postural adjustments assessment during step initiation in patients with leprosy.

Anticipatory postural adjustments (APAs) involve a complex coordination of sensorimotor information that can be impaired in diseases that affect nerve conduction. Assessing APAs typically requires costly video recording technology, posing a challenge to the study of postural changes. This hurdle is compounded in impoverished communities affected by diseases such as leprosy, which often receive limited government support. Recent years have seen the validation of inertial sensors in wearable devices and smartphones for APA analysis in diverse populations, including adults, the elderly and people with Parkinson's disease. This progress offers economically efficient alternatives for the study of APA in leprosy. Do patterns of activation of anticipatory postural adjustment differ between leprosy patients and healthy controls? We also investigated the validity and replicability of APAs recorded in leprosy patients using inertial measurements and video capture recordings. Thirty healthy individuals in the control group and 30 individuals with leprosy in the leprosy group performed ten gait initiation trials. To record the APA for gait initiation, the participants stood on a 2 m platform. Each participant was informed that the experimenter would give an signal, after which the participant would initiate a two-step walk on the platform. Inertial recordings (low-cost method) and video capture recordings (gold-standard method) from center of mass displacements were used to extract the APA before gait initiation. The results show that APAs are similar between groups (control and leprosy), but leprosy patients have less consistent APAs. In addition, this study highlights the reproducibility and high correlation between the values of variables obtained from both instruments, the video recording as gold standard method and portable digital inertial sensor as a low-cost alternative method. These promising findings support the use of affordable inertial sensors to track and record APAs in underserved populations that lack easy access to gold standard methods such as video recording. This approach has the potential to improve the therapeutic care and rehabilitation of these patients. Although not currently part of official protocols for leprosy patients, this assessment method could prove particularly valuable in situations where significant sensorimotor impairments are suspected or documented.

Exploring the role of anticipatory postural adjustment duration within APA2 subphase as a potential mediator between clinical disease severity and fall risk in Parkinson's disease.

Introduction: People with Parkinson's Disease (PD) often show reduced anticipatory postural adjustments (APAs) before voluntary steps, impacting their stability. The specific subphase within the APA stage contributing significantly to fall risk remains unclear. Methods: We analyzed center of pressure (CoP) trajectory parameters, including duration, length, and velocity, throughout gait initiation. This examination encompassed both the postural phase, referred to as anticipatory postural adjustment (APA) (APA1, APA2a, APA2b), and the subsequent locomotor phases (LOC). Participants were instructed to initiate a step and then stop (initiating a single step). Furthermore, we conducted assessments of clinical disease severity using the Unified Parkinson's Disease Rating Scale (UPDRS) and evaluated fall risk using Tinetti gait and balance scores during off-medication periods. Results: Freezing of gait (FOG) was observed in 18 out of 110 participants during the measurement of CoP trajectories. The Ramer-Douglas-Peucker algorithm successfully identified CoP displacement trajectories in 105 participants (95.5%), while the remaining 5 cases could not be identified due to FOG. Tinetti balance and gait score showed significant associations with levodopa equivalent daily dose, UPDRS total score, disease duration, duration (s) in APA2a (s) and LOC (s), length in APA1 (cm) and APA2b (cm), mediolateral velocity in APA1 (X) (cm/s), APA2a (X) (cm/s), APA2b (X) (cm/s) and LOC (X) (cm/s), and anterior-posterior velocity in APA2a (Z) (cm/s) and APA2b (Z) (cm/s). Multiple linear regression revealed that only duration (s) in APA2a and UPDRS total score was independently associated with Tinetti gait and balance score. Further mediation analysis showed that the duration (s) in APA2a served as a mediator between UPDRS total score and Tinetti balance and gait score (Sobel test, p = 0.047). Conclusion: APA2 subphase duration mediates the link between disease severity and fall risk in PD, suggesting that longer APA2a duration may indicate reduced control during gait initiation, thereby increasing fall risk.

Effects of Combining Transcranial Direct Current Stimulation With Balance Training on Anticipatory Postural Adjustments in Persons With Chronic Ankle Instability.

BACKGROUND: The combination of transcranial direct current stimulation (tDCS) with balance training could integrate central and peripheral neural mechanisms. This study aimed to investigate the effects of concurrent balance training and tDCS over the supplementary motor area (SMA) on anticipatory postural adjustments during gait initiation (GI) in persons with chronic ankle instability (CAI). HYPOTHESIS: Balance training will increase the center of pressure (COP) velocity and displacement during GI phases in all participants, and those receiving real tDCS will show greater increases. STUDY DESIGN: Randomized controlled trial. LEVEL OF EVIDENCE: Level 2. METHODS: A total of 32 subjects were allocated to 2 groups: (1) intervention (balance training plus real tDCS) and (2) control (balance training plus sham tDCS). Outcome measures were COP-related parameters (displacement and velocity) during phases of GI (anticipatory, weight transition, and locomotor). RESULTS: The results showed that, in the anticipatory phase, the anteroposterior displacement of the COP was increased significantly at posttest relative to pretest across both groups, F(1,30) = 5.733, P = 0.02. In addition, both groups revealed an increase in the mediolateral COP velocity at posttest, F(1,30) = 10.523, P < 0.01. In the weight transition phase, both groups had higher mediolateral COP velocity at posttest, F(1,30) = 30.636, P < 0.01. In the locomotor phase, in both groups, the anteroposterior COP velocity was increased significantly at posttest compared with pretest, F(1,30) = 5.883, P = 0.02. CONCLUSION: Both groups demonstrated improvements in the anticipatory and execution phases of GI. Since no between-group difference was found, it can be interpreted that the anodal tDCS applied over the SMA has no added value over sham stimulation. CLINICAL RELEVANCE: Balance training is beneficial for persons with CAI and can improve the anticipation and execution phases of GI without the aid of brain stimulation.

Analysis of the characteristics of anticipatory postural adjustments in older adults using smartphones: Association between cognitive and balance functions.

OBJECTIVES: Using smartphones, we aimed to clarify the characteristics of anticipatory postural adjustments (APA) in older adults and examine the relationship between cognitive and balance functions. METHODS: The study participants were 10 young and 13 older adults. An accelerometer built into a smartphone was attached to the lower back (L5) of the participant, and acceleration in the mediolateral direction was measured using a one-leg stance (OLS). As APA features, we analyzed the time to the peak value in the stance direction (peak latency [PL]) and the amount of displacement to the peak value in the stance direction (peak magnitude [PM]). Additionally, the measured PL was divided by PM for each group to obtain the APA ratio (APAr). We investigated the relationship between the APAr and Mini-BESTest subitems. RESULTS: Older adults showed delayed PL and decreased PM levels (p < 0.01). While in the Mini-BESTest sub-items, deductions were most common in the order of dual-task and single-leg standing, and most participants with low APAr scores were degraded in APA of sub-items. The correlation was observed between APAr and both TUG and dual-task cost (DTC) (r= -0.56, r= -0.67). According to the receiver operating characteristic curve, the APAr value was 1.71 in the older age group. CONCLUSIONS: Older adults showed delayed PL and decreased PM, and APAr was associated with cognitive and locomotor functions. By evaluating the APAr at the initiation of movement, it may be possible to distinguish the APA of the older adluts from the possible to the impossible of OLS movement.

Predicting slight freezing of gait in Parkinson's disease with anticipatory postural adjustments and limits of stability.

INTRODUCTION: Gait initiation (GI) includes automatic and voluntary movements. However, research on their impact on the first step in patients with Parkinson's disease (PD) and their relationship to freezing of gait (FOG) is lacking. We examined the effects of automatic movements (anticipatory postural adjustments [APAs]) and voluntary movements (limits of stability [LOS]) on the first step (first-step duration and first-step range of motion), along with their early recognition and prediction of slight FOG. METHODS: Twenty-three patients with PD and slight freezing (PD + FOG) and 25 non-freezing patients with PD (PD-FOG) were tested while off medications and compared with 24 healthy controls (HC). All participants completed a 7-m Stand and Walk Test (7 m SAW) and wore inertial sensors to quantify the APAs and first step. LOS was quantified by dynamic posturography in different directions using a pressure platform. We compared differences among all three groups, analysed correlations, and evaluated their predictive value for slight FOG. RESULTS: In PD + FOG, APAs and LOS were worse than those in the PD-FOG and HC groups (p < 0.001), and the first step was worse than that in HC (p < 0.001). APAs were correlated mainly with the first-step duration. APAs and LOS were correlated with the first-step range of motion. APAs have been recognized as independent predictors of FOG, and their combination with LOS enhances predictive sensitivity. CONCLUSION: APAs and LOS in patients with PD directly affect the first step during GI. In addition, the combination of APAs and LOS helped predict slight FOG.

Treadmill induced belt-accelerations may not accurately evoke the muscle responses to obstacle trips in older people.

BACKGROUND: Treadmill belt-accelerations are a commonly utilised surrogate for tripping, but their physiological validity is unknown. This study examined if a treadmill belt-acceleration induces lower limb muscle activation responses similar to a trip on a walkway. METHODS: 38 older people (65+ years) experienced one treadmill belt-acceleration and one walkway obstacle trip in random order. Muscle responses were assessed bilaterally using surface electromyography on the rectus femoris (RF), tibialis anterior (TA), semitendinosus (ST) and gastrocnemius medial head (GM). Unperturbed muscle activity, post-perturbation onset latency, peak magnitude, time to peak and co-contraction index (CCI) were examined. RESULTS: Muscle activity in the right ST was greater during unperturbed walking on the treadmill compared to walkway (P=0.011). Compared to a treadmill belt-acceleration, a walkway trip elicited faster onset latencies in all muscles; greater peak magnitudes in the left RF, TA, GM and right GM; faster time to peaks in the left TA and right GM; and lower knee and ankle muscle CCI (P<0.05). CONCLUSIONS: Walkway trips and treadmill belt-accelerations elicit distinct muscle activation patterns. While walkway trips induced faster and larger muscle responses, treadmill belt-accelerations involved greater co-contraction. Therefore, treadmill belt-accelerations may not accurately simulate the muscle responses to trips.

Gait initiation in Parkinson's disease: comparison of timing and displacement during anticipatory postural adjustments as a function of motor severity and apathy in a large cohort.

Introduction: Gait initiation is preceded by three anticipatory postural adjustment (APA) phases. In Parkinson's disease (PD) generated force, displacement and timing during APA differ from healthy controls. APA might be influenced by disease status, weight or emotion. It is unknown how motor severity, disease duration or presence of apathy influences APA timing and displacement. Methods: We included 99 people with PD and 50 healthy controls (HC) to perform five gait initiation trials following an auditory cue. Force plates measured timing and center of pressure (CoP) displacement during APA phases. Results: Time to gait initiation (tGI) was higher in the PD group (p < 0.001, t = 2.74, 95%CI (0.008, 0.066)). The first two APA phases (APA1 and APA2a) lasted longer in PD (respectively p < 0.001, t = 3.87, 95%CI (0.091, 0.28) and p < 0.001, t = 4.1, 95%CI (0.031, 0.091)). Mean CoP displacement, variability in timing and displacement did not differ. A multiple regression model was used to determine if clinical variables were related to gait initiation parameters. tGI was predicted by age (p < 0.001) and weight (p = 0.005). The duration of APA1 was predicted by weight (p = 0.006) and APA2a by age (p < 0.001). Variability in duration of the locomotor phase (LOC) was predicted by age (p < 0.001). Conclusion: tGI and initial APA phases are longer in PD than in HC. There are no significant differences in variability of timing or displacement between the two groups. Gait initiation parameters are independent of disease duration, motor severity, medication usage or apathy in PD. Our findings suggest that cueing does not speed up gait initiation but reduces variability.

Cerebellar Transcranial Direct Current Stimulation Modulates Anticipatory Postural Adjustments in Healthy Adults.

During forward swinging of the arm, the central nervous system must anticipate the effect of upraising upon the body. Little is known about the cerebellar network that coordinates these anticipatory postural adjustments (APAs). Stimulating different cerebellar regions with transcranial direct current stimulation (tDCS) and with different polarities modulated the APAs. We used surface electromyography (sEMG) to measure muscle activities in a bilateral rapid shoulder flexion task. The onset of APAs was altered after tDCS over the vermis, while the postural stability and the kinematics of arm raising were not affected. To our knowledge, this is the first human cerebellar-tDCS (c-tDCS) study to separate cerebellar involvement in core muscle APAs in bilateral rapid shoulder flexion. These data contribute to our understanding of the cerebellar network supporting APAs in healthy adults. Modulated APAs of the erector spinae by tDCS on the vermis may be related to altered cerebellar brain inhibition (CBI), suggesting the importance of the vermal-cerebral connections in APAs regulation.

Characterization of temporal and intensity parameters of early postural adjustment phase during gait initiation in stroke patients / 中国组织工程研究

BACKGROUND:Early postural adjustments serve as preparatory measures for forthcoming actions or potential disruptions in posture,thereby facilitating improved movement execution and mitigating destabilizing effects caused by posture interference. OBJECTIVE:To investigate the characteristics of temporal and intensity parameters of key lower limb muscles during early postural adjustment phase when stroke patients with varying levels of balance initiate walking at a self-selected comfortable pace. METHODS:The characteristics of early postural adjustments in 16 stroke patients were observed.Sixteen patients were divided into a non-fall group(n=8)and a fall group(n=8)based on the history of falls and Berg Balance Scale scores.Noraxon inertial sensors and Noraxon Ultium EMG wireless surface electromyography were utilized to collect body kinematic data and surface electromyography data during gait initiation.Muscle activation time and activation sequence of six key muscles in the lower limbs(tibialis anterior,medial and lateral gastrocnemius,rectus femoris,lateral femoris and biceps femoris muscles)during the early postural adjustment phase,as well as normalized electromyography integral values for the four time windows(each 150 ms)before gait initiation,were analyzed. RESULTS AND CONCLUSION:Stroke patients with a history of falls exhibited earlier activation times for the six key muscles in the lower limbs during gait initiation compared with those in the non-fall group.The fall group demonstrated significantly earlier activation times for tibialis anterior,lateral head of gastrocnemius,and vastus lateralis(P<0.01,P<0.05).In contrast,the non-fall group displayed a consistent pattern of activating extensor muscles before flexor muscles,with thigh muscle activation preceding calf muscle activation.However,in the fall group,calf extensor muscle activation occurred prior to thigh extensor muscle activation,and the vastus lateralis was activated even earlier.The tibialis anterior was the last activated muscle in both groups.Specifically during T3(>-300 to-150 ms),the tibialis anterior exhibited significantly higher activity in the fall group compared with the non-fall group(P<0.05),while the lateral head of gastrocnemius demonstrated significant inhibition during T3(P<0.05)and the medial head of gastrocnemius showed significant inhibition during both T3 and T4(>-150 to 0 ms)stages compared with the non-fall group(P<0.01,P<0.05).To conclude,stroke patients with varying balance abilities employ distinct early postural adjustment strategies prior to stepping,as evidenced by differences in muscle activation timing,recruitment order,and muscle activity amplitude.Patients at a high risk of falling exhibit prolonged duration of early postural adjustment and delayed initiation of gait,indicating earlier activation of the tibialis anterior muscle and inhibition of gastrocnemius muscle activity.These delays in gait initiation and variations in muscle recruitment strategies may contribute to unstable posture and an increased susceptibility to falls.

Effect of Chronic Ankle Instability on the Biomechanical Organization of Gait Initiation: A Systematic Review.

This systematic review was conducted to provide an overview of the effects of chronic ankle instability (CAI) on the biomechanical organization of gait initiation. Gait initiation is a classical model used in the literature to investigate postural control in healthy and pathological individuals. PubMed, ScienceDirect, Scopus, Web of Science, and Google Scholar were searched for relevant articles. Eligible studies were screened and data extracted by two independent reviewers. An evaluation of the quality of the studies was performed using the Downs and Black checklist. A total of 878 articles were found in the initial search, but only six studies met the inclusion criteria. The findings from the literature suggest that CAI affects the characteristics of gait initiation. Specifically, individuals with CAI exhibit notable differences in reaction time, the spatiotemporal parameters of anticipatory postural adjustments (APAs) and step execution, ankle-foot kinematics, and muscle activation compared to healthy controls. In particular, the observed differences in APA patterns associated with gait initiation suggest the presence of supraspinal motor control alterations in individuals with CAI. These findings may provide valuable information for the rehabilitation of these patients. However, the limited evidence available calls for caution in interpreting the results and underscores the need for further research.

Gait initiation in multiple sclerosis patients with and without functional loss.

BACKGROUND: Gait initiation (GI) is an important functional task related to balance and gait performance. In addition, it has predictive importance for falls and postural instability in patient with multiple sclerosis (MS). However, it is uncertain how GI is affected in patients in the early stage of MS (Expanded Disability Status Scale (EDSS) ≤3). In this study, it was aimed to investigate the anticipatory postural adjustments (APAs), posterior center of pressure (COPap) displacement, and spatiotemporal variability during GI in patients with and without functional loss in the early stage of MS. METHODS: Forty-four participants (31 MS patients and 13 healthy subjects) involved in this prospective cross-sectional study were divided into three groups: Group-I: Patients without functional loss (EDSS 0 to 1.5) (n = 14), Group-II: Patients with functional loss (EDSS 2 to 3) (n = 17) and Group-III: Healthy subjects (n = 13). Electromyographic activity of the bilateral tibialis anterior (TA) and gastrocnemius medialis (GM) and COPap displacement were recorded during the postural phase of GI. Additionally, spatiotemporal parameters were recorded within the first three steps, and the coefficient of variation was calculated with 40 walks for variability. RESULTS: There were significant differences in the Kruskal-Wallis tests of variables (p<0.05). Group-I demonstrated smaller APAs magnitudes in TA [stance (p = 0.01), swing (p = 0.01)], GM of swing limb (p<0.0001), and smaller COPap displacement (p<0.0001) compared to group-III. Group-II demonstrated smaller APAs magnitudes in all muscles (p<0.0001) compared to group-III and the smallest COPap displacement (p<0.0001). Group-I showed a significant increase in stride width variability compared to group-III (p = 0.01). Group-II showed a significant increase in several variabilities [first stride length (p<0.0001), second stride time (p<0.0001), first double support time (p<0.0001), stride width (p<0.0001)] compared to group-III. CONCLUSION: Patients in the early stage of MS had impairment in both the postural and locomotor phases of GI with more obvious in the patients with functional loss. The results indicate that MS patients without functional loss have difficulty initiating gait. Although there is no functional loss, the patients have a risk of falls, postural instability, and gait impairment due to their inability to initiate gait effectively. As a result, rehabilitation is necessary even if there is no functional loss in patients with MS.

Evidence for an Intricate Relationship Between Express Visuomotor Responses, Postural Control and Rapid Step Initiation in the Lower Limbs.

Recent work has described express visuomotor responses (EVRs) on the upper limb. EVRs are directionally-tuned bursts of muscle activity that occur within 100 ms of visual stimulus appearance, facilitating rapid reaching. Rapid stepping responses are also important in daily life, and while there is evidence of EVR expression on lower limbs, it is unknown whether lower-limb EVRs are influenced by increased postural demands. Here, we investigate the interaction between stepping-related EVRs and anticipatory postural adjustments (APAs) that typically precede step initiation. 16 healthy young subjects rapidly stepped towards visual targets presented in front of the left or right foot. We recorded bilateral surface EMG of gluteus medius (GM), a muscle involved in both APAs and stepping, and bilateral ground reaction forces. Two conditions were introduced: an anterolateral or anteromedial stepping condition with reduced or increased postural demands, respectively. In the anterolateral stepping condition, EVRs were robustly and strongly present in stance-side GM, and ground reaction forces revealed strongly decreased expression of APAs. Larger EVRs preceded shorter RTs, consistent with EVRs facilitating step initiation. In contrast, in the anteromedial stepping condition, EVRs were largely absent, and ground reaction forces revealed the consistent expression of APAs. When occasionally present, EVRs in the anteromedial stepping condition preceded larger APAs and longer RTs. Thus, while EVRs in lower limbs can facilitate rapid stepping, their expression is normally suppressed when postural stability is low. Failing to appropriately suppress EVRs in such situations disrupts postural stability, necessitating larger compensatory APAs and leading to longer stepping RTs.

Explanatory Capacity of Postural Control and Physical Fitness in Cognitive Impairment and Support Needs among Individuals with Intellectual Disabilities-A Cross-Sectional Pilot Study.

Postural control is a skill associated with most motor activities and is essential for the performance of activities of daily living. People with intellectual disabilities (ID) present postural control deficits that can be attributed to several causes. The aim of this study was to determine whether postural control and physical fitness could explain the cognitive impairment and support needs in this population. A cross-sectional pilot study was conducted with 18 people with ID. Data collection was based on assessments for postural control (Mini BESTest and Berg Balance Scale) and physical fitness (Senior Fitness Test). The data were analyzed using linear regression models. Anticipatory postural adjustments were associated with support needs, explaining up to 45% of these. Consecutive postural adjustments and upper limb strength were less significantly associated with support needs. However, none of the variables used explained cognitive impairment in ID. Knowledge of the relationships and behavior of the different measurement tools is essential for the development of appropriate interventions in this population.