Vertical Center-of-Mass Braking and Motor Performance during Gait Initiation in Young Healthy Adults, Elderly Healthy Adults, and Patients with Parkinson's Disease: A Comparison of Force-Plate and Markerless Motion Capture Systems.

BACKGROUND: This study tested the agreement between a markerless motion capture system and force-plate system ("gold standard") to quantify stability control and motor performance during gait initiation. METHODS: Healthy adults (young and elderly) and patients with Parkinson's disease performed gait initiation series at spontaneous and maximal velocity on a system of two force-plates placed in series while being filmed by a markerless motion capture system. Signals from both systems were used to compute the peak of forward center-of-mass velocity (indicator of motor performance) and the braking index (indicator of stability control). RESULTS: Descriptive statistics indicated that both systems detected between-group differences and velocity effects similarly, while a Bland-Altman plot analysis showed that mean biases of both biomechanical indicators were virtually zero in all groups and conditions. Bayes factor 01 indicated strong (braking index) and moderate (motor performance) evidence that both systems provided equivalent values. However, a trial-by-trial analysis of Bland-Altman plots revealed the possibility of differences >10% between the two systems. CONCLUSION: Although non-negligible differences do occur, a markerless motion capture system appears to be as efficient as a force-plate system in detecting Parkinson's disease and velocity condition effects on the braking index and motor performance.

Principal Component Analysis Enhanced with Bootstrapped Confidence Interval for the Classification of Parkinsonian Patients Using Gaussian Mixture Model and Gait Initiation Parameters.

Parkinson's disease is one of the major neurodegenerative diseases that affects the postural stability of patients, especially during gait initiation. There is actually an increasing demand for the development of new non-pharmacological tools that can easily classify healthy/affected patients as well as the degree of evolution of the disease. The experimental characterization of gait initiation (GI) is usually done through the simultaneous acquisition of about 20 variables, resulting in very large datasets. Dimension reduction tools are therefore suitable, considering the complexity of the physiological processes involved. The principal Component Analysis (PCA) is very powerful at reducing the dimensionality of large datasets and emphasizing correlations between variables. In this paper, the Principal Component Analysis (PCA) was enhanced with bootstrapping and applied to the study of the GI to identify the 3 majors sets of variables influencing the postural control disability of Parkinsonian patients during GI. We show that the combination of these methods can lead to a significant improvement in the unsupervised classification of healthy/affected patients using a Gaussian mixture model, since it leads to a reduced confidence interval on the estimated parameters. The benefits of this method for the identification and study of the efficiency of potential treatments is not addressed in this paper but could be addressed in future works.

Evaluation of the Margin of Stability during Gait Initiation in Young Healthy Adults, Elderly Healthy Adults and Patients with Parkinson's Disease: A Comparison of Force Plate and Markerless Motion Capture Systems.

Gait initiation (GI) is a functional task classically used in the literature to evaluate the capacity of individuals to maintain postural stability. Postural stability during GI can be evaluated through the "margin of stability" (MoS), a variable that is often computed from force plate recordings. The markerless motion capture system (MLS) is a recent innovative technology based on deep learning that has the potential to compute the MoS. This study tested the agreement between a force plate measurement system (FPS, gold standard) and an MLS to compute the MoS during GI. Healthy adults (young [YH] and elderly [EH]) and Parkinson's disease patients (PD) performed GI series at spontaneous (SVC) and maximum velocity (MVC) on an FPS while being filmed by a MLS. Descriptive statistics revealed a significant effect of the group (YH vs. EH vs. PD) and velocity condition (SVC vs. MVC) on the MoS but failed to reveal any significant effect of the system (MLS vs. PFS) or interaction between factors. Bland-Altman plot analysis further showed that mean MoS biases were zero in all groups and velocity conditions, while the Bayes factor 01 indicated "moderate evidence" that both systems provided equivalent MoS. Trial-by-trial analysis of Bland-Altman plots, however, revealed that differences of >20% between the two systems did occur. Globally taken, these findings suggest that the two systems are similarly effective in detecting an effect of the group and velocity on the MoS. These findings may have important implications in both clinical and laboratory settings due to the ease of use of the MLS compared to the FPS.

Influence of temporal pressure constraint on the biomechanical organization of gait initiation made with or without an obstacle to clear.

Many daily motor tasks have to be performed under a temporal pressure constraint. This study aimed to explore the influence of such constraint on motor performance and postural stability during gait initiation. Young healthy participants initiated gait at maximal velocity under two conditions of temporal pressure: in the low-pressure condition, gait was self-initiated (self-initiated condition, SI); in the high-pressure condition, it was initiated as soon as possible after an acoustic signal (reaction-time condition, RT). Gait was initiated with and without an environmental constraint in the form of an obstacle to be cleared placed in front of participants. Results showed that the duration of postural adjustments preceding swing heel-off ("anticipatory postural adjustments", APAs) was shorter, while their amplitude was larger in RT compared to SI. These larger APAs allowed the participants to reach equivalent postural stability and motor performance in both RT and SI. In addition, the duration of the execution phase of gait initiation increased greatly in the condition with an obstacle to be cleared (OBST) compared to the condition without an obstacle (NO OBST), thereby increasing lateral instability and thus involving larger mediolateral APA. Similar effects of temporal pressure were obtained in NO OBST and OBST. This study shows the adaptability of the postural system to temporal pressure in healthy young adults initiating gait. The outcome of this study may provide a basis for better understanding the aetiology of balance impairments with the risk of falling in frail populations while performing daily complex tasks involving a whole-body progression.

Directional specificity of postural threat on anticipatory postural adjustments during lateral leg raising.

This study explored the directional specificity of fear of falling (FoF) effects on the stabilizing function of anticipatory postural adjustments (APA). Participants (N = 71) performed a series of lateral leg raises from an elevated surface in three conditions: in the "Control condition", participants stood at the middle of the surface; in the two test conditions, participants were positioned at the lateral edge of the surface so that the shift of the whole-body centre-of-mass during APA for leg raising was directed towards the edge ("Approach condition") or was directed away from the edge ("Avoidance condition"). Results showed that the amplitude of APA was lower in the "Approach condition" than in the "Control condition" (p < .01); this reduction was compensated for by an increase in APA duration (p < .05), so that both postural stability and motor performance (in terms of peak leg velocity, final leg posture and movement duration) remained unchanged. These changes in APA parameters were not present in the "Avoidance condition". Participants further self-reported a greater FoF (p < .001) and a lower ability to avoid a fall (p < .001) in the "Approach condition" (but not in the "Avoidance condition") than in the "Control condition". The results of this study show that the effects of FoF do not solely depend on initial environmental conditions, but also on the direction of APA relative to the location of the postural threat. These results support the so-called Motivational Direction Hypothesis, according to which approach and avoidance behaviours are primed by emotional state.

Influence of ankle loading on the relationship between temporal pressure and motor coordination during a whole-body paired task.

We investigated whether ankle loading modifies the relationship between temporal pressure and motor coordination during a whole-body paired task. Eight young healthy adults standing in an erect posture performed multiple series of simultaneous rapid leg flexions paired with ipsilateral index finger extensions. They repeated the task ten times in three load conditions: unloaded, loaded (where additional 5-kg inertia was attached to the ankles), and post-loaded (immediately following the loaded condition). These conditions were conducted in two blocks of temporal pressure: self-initiated (SI) versus reaction time (RT). When participants were unloaded, the results showed that index finger extension preceded swing heel-off in RT, and conversely in SI. By contrast, when the participants were loaded, swing heel-off preceded index finger extension in both SI and RT, showing that loading modified the relationship between temporal pressure and movement synchronization in RT only. However, loading did not induce any increase in the error of synchronization. Furthermore, in both the unloaded and loaded conditions, the duration of "anticipatory postural adjustments" (APA) was shorter when the temporal pressure was increased. Interestingly, the shorter APA duration was compensated by an increase in APA amplitude. Thus, loading did not modify the relationship between temporal pressure and anticipatory postural dynamics. Post-loaded and unloaded conditions produced the same results. These results show that the central nervous system optimally adapts the relationship between temporal pressure and motor coordination to transitory changes in the mechanical properties of the lower limbs, here due to ankle loading.

Impact of lumbar delayed-onset muscle soreness on postural stability in standing postures.

BACKGROUND: Similar impact on proprioception has been observed in participants with lumbar delayed-onset muscle soreness (DOMS) and chronic low back pain (LBP), raising questions about the relevance of lumbar DOMS as a suitable pain model for LBP when assessing back pain-related postural stability changes. RESEARCH QUESTION: Does lumbar DOMS impact postural stability? METHODS: Twenty healthy adults participated in this experimental study and underwent a posturographic examination before and 24 to 36 h after a protocol designed to induce lumbar DOMS. Posturographic examination was assessed during quiet standing on both feet with eyes opened (EO), with eyes closed (EC), and on one-leg (OL) standing with eyes opened. Postural stability was assessed through center of pressure (COP) parameters (COP area, velocity, root mean square, mean power frequency) which were compared using repeated measure ANOVA. Moreover, pain, soreness and pressure pain threshold (PPT) on specific muscles were assessed. RESULTS: There was a significant main effect of the postural condition on all COP variables investigated. More specifically, each COP variable reached a significantly higher value in the OL stance condition than in both EO and EC bipedal conditions (all with p < 0.001). In addition, the COP velocity and the mean power frequency along the anteroposterior direction both reached a significantly higher value in EC than in EO (p < 0.001). In contrast, there was no significant main effect of the DOMS nor significant DOMS X postural condition interaction on any of the COP variables. There was a significant decrease in the PPT value for both the left and right erector spinae muscles, as well as the left biceps femoris. SIGNIFICANCE: Lumbar DOMS had no impact on postural stability, which contrasts findings in participants with clinical LBP. Although DOMS induces similar trunk sensorimotor adaptations to clinical LBP, it does not appear to trigger similar postural stability adaptations.

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.

Sport dependent effects on the sensory control of balance during upright posture: a comparison between professional horseback riders, judokas and non-athletes.

Introduction: Compared to judokas (JU) and non-athletes (NA), horseback riders (HR) may develop specific changes in their sensory control of balance. Methods: Thirty-four international-level JU, twenty-seven international-level HR and twenty-one NA participated. Participants stood upright on a plateform (static condition) or on a seesaw device with an instability along the mediolateral (ML) or the anteroposterior (AP) direction (dynamic conditions). These conditions were carried out with eyes opened (EO) or closed (EC), and with (wF) or without a foam (nF). Experimental variables included conventional (linear), non-linear center-of-pressure (COP) parameters, Romberg Quotient (RQ) and Plantar Quotient (PQ). Results: Group effects. COP Surface (COPS) and standard deviation of COP along AP (SDY) were lower in HR than in JU in Static. SD Y was lower in HR than in JU in Dynamic AP. COP velocity (COPV) was lower in both HR and JU than in NA in Static and Dynamic. Sample entropy along AP and ML (SampEnY and SampEnX) were higher in HR than in JU in Static. SampEnY was higher in HR than in JU in Dynamic ML. Sensory effects. In EC, COPV was lower in JU than in NA in Dynamic AP, and lower in JU than in both HR and NA in Dynamic ML. In EO, COPV was lower in both JU and HR than in NA in Dynamic ML. RQ applied to COPS was lower in JU than in both HR and NA in Dynamic AP, and lower in JU than in HR in Dynamic ML. RQ applied to COPV was lower in JU than in both HR and NA in Static and Dynamic. PQ applied to COPS was higher in JU than in both HR and NA in Dynamic ML. Conclusion: Results showed that the effects of sport expertise on postural control could only be revealed with specific COP variables and were directionally oriented and sport-dependant. HR seem to rely more on vision than JU, thus revealing that the contribution of the sensory inputs to balance control is also sport-dependent. Results open up new knowledge on the specificity of sport practice on multisensory balance information during upright posture.

Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings.

Gait initiation (GI), the transient phase between orthograde posture and steady-state locomotion, is a functional task and an experimental paradigm that is classically used in the literature to obtain insight into the basic postural mechanisms underlying body motion and balance control. Investigating GI has also contributed to a better understanding of the physiopathology of postural disorders in elderly and neurological participants (e.g., patients with Parkinson's disease). As such, it is recognized to have important clinical implications, especially in terms of fall prevention. This paper aims to provide scholars, clinicians, and higher education students information on the material and method developed to investigate GI postural organization via a biomechanical approach. The method is based on force platform recordings and the direct principle of mechanics to compute the kinematics of the center of gravity and center of pressure. The interaction between these two virtual points is a key element in this method since it determines the conditions of stability and whole-body progression. The protocol involves the participant initially standing immobile in an upright posture and starting to walk until the end of an at least 5 m track. It is recommended to vary the GI velocity (slow, spontaneous, fast) and the level of temporal pressure - gait may be initiated as soon as possible after the deliverance of a departure signal (high level of temporal pressure) or when the participant feels ready (low level of temporal pressure). Biomechanical parameters obtained with this method (e.g., duration and amplitude of anticipatory postural adjustments, step length/width, performance, and stability) are defined, and their computation method is detailed. In addition, typical values obtained in healthy young adults are provided. Finally, critical steps, limitations, and significance of the method with respect to the alternative method (motion capture system) are discussed.

Acute effects of short-term stretching of the triceps surae on ankle mobility and gait initiation in patients with Parkinson's disease.

BACKGROUND: Ankle mobility is known to be of uttermost importance to generate propulsive forces and control balance during gait initiation. Impaired mobility of the postural chain occurs with normal ageing and is exacerbated in patients with Parkinson's disease. This study questions whether short-term stretching session applied to the triceps surae improves ankle mobility and, consequently, dynamical postural control in patients with Parkinson's disease performing gait initiation. METHOD: Nineteen patients with Parkinson's disease participated in this study and were randomly assigned to an "intervention group" or a "sham group". In the intervention group, patients were exposed to a 4 × 60 seconds triceps surae stretching. In the sham group, they were exposed to forearm stretching. Additionally, ten age-matched healthy elderly, who were not exposed to any stretching-treatment, were assigned to a "control group". Participants performed series of gait initiation on a force-plate before and after their treatment. FINDINGS: Ankle mobility was improved in the intervention group after triceps surae stretching. The forward velocity of the center-of-mass at heel-off and motor performance related-parameters (progression velocity, center-of-mass velocity at foot-contact and swing phase duration) were also improved in the intervention group, with large effect sizes (d ≥ 0.8). None of the stability parameters were modified by the treatments. INTERPRETATION: Short-term triceps surae stretching is an efficient method to increase ankle mobility and improve the capacity to generate forward propulsive forces in patients with Parkinson's disease. These findings are congruent with the "posturo-kinetics capacity" theory according to which dynamical postural control depends on postural chain mobility.

In Patients With Parkinson's Disease in an OFF-Medication State, Does Bilateral Electrostimulation of Tibialis Anterior Improve Anticipatory Postural Adjustments During Gait Initiation?

A complete lack of bilateral activation of tibialis anterior (TA) during gait initiation (GI), along with bradykinetic anticipatory postural adjustments (APAs), often occurs in patients with Parkinson's disease (PD) in their OFF-medication state. Functional electrical stimulation (FES) is a non-pharmacological method frequently used in neurorehabilitation to optimize the effect of L-DOPA on locomotor function in this population. The present study tested the potential of bilateral application of FES on TA to improve GI in PD patients. Fourteen PD patients (OFF-medication state, Hoehn and Yahr state 2-3) participated in this study. They performed series of 10 GI trials on a force-plate under the following experimental conditions: (1) GI without FES (control group), (2) GI with 2Hz-FES (considered as a very low FES frequency condition without biomechanical effect; placebo group) and (3) GI with 40Hz-FES (test group). In (2) and (3), FES was applied bilaterally to the TA during APAs (300 mA intensity/300 µs pulse width). Main results showed that the peak of anticipatory backward center of pressure shift, the forward center of mass (COM) velocity and shift at foot off were significantly larger in the 40 Hz FES condition than in the control condition, while the duration of step execution was significantly shorter. In contrast, the capacity of participants to brake the fall of their COM remained unchanged across conditions. Globally taken, these results suggest that acute application of 40-Hz FES to the TA may improve the capacity of PD patients to generate APAs during GI, without altering their balance capacity. Future studies are required before considering that TA FES application might be a valuable tool to improve GI in PD patients and be relevant to optimize the effects of L-DOPA medication on locomotor function.

The role(s) of "Simultaneous Postural Adjustments" (SPA) during Single Step revealed with the Lissajous method.

Dynamical phenomena in the postural chain occur before, during and after the voluntary movement. These phenomena correspond to anticipatory (APA), simultaneous (SPA), and consecutive (CPA) postural adjustments, respectively. APA and, more recently, CPA, have been extensively investigated in the literature. SPA have surprisingly received much less attention. The aim of the present study was to examine the role(s) of SPA associated with a single step task (SST). Ten healthy young adults performed series of SST on a force-plate. A 2-DOF mechanical model was used to separate the dynamics of the swing leg and the dynamics of the rest of the body, corresponding to the focal and the postural component of the SST, respectively. The postural component was plotted against the focal one during SPA (from heel-off to foot-contact), and this plot was modelled as a Lissajous ellipse. Result showed that this ellipse systematically ran through the same three quadrants of the diagram. For each of these quadrants, the role of the postural component in regards to the focal one was interpreted according to the relative orientation of the postural and focal dynamics. Results thus showed that SPA ensured the following successive roles: counter-perturbation of swing leg dynamics following heel-off, propulsion of swing leg, counter-perturbation of swing leg dynamics again, and then braking swing leg movement. These new findings contribute to a better knowledge of postural adjustments properties, and may provide new insights for understanding balance troubles with aging and in neurological patients (e.g. people with Parkinson's disease).

Effects of stretching exercises on human gait: a systematic review and meta-analysis.

Background: Stretching is commonly used in physical therapy as a rehabilitation tool to improve range of motion and motor function. However, is stretching an efficient method to improve gait, and if so, for which patient category? Methods: A systematic review of randomized and non-randomized controlled trials with meta-analysis was conducted using relevant databases. Every patient category and every type of stretching programs were included without multicomponent programs. Data were meta-analysed where possible. Estimates of effect sizes (reported as standard mean difference (SMD)) with their respective 95% confidence interval (95% CI) were reported for each outcome. The PEDro scale was used for the quality assessment. Results: Twelve studies were included in the analysis. Stretching improved gait performance as assessed by walking speed and stride length only in a study with a frail elderly population, with small effect sizes (both SMD= 0.49; 95% CI: 0.03, 0.96; PEDro score: 3/10). The total distance and the continuous walking distance of the six-minute walking test were also improved only in a study in an elderly population who had symptomatic peripheral artery disease, with large effect sizes (SMD= 1.56; 95% CI: 0.66, 2.45 and SMD= 3.05; 95% CI: 1.86, 4.23, respectively; PEDro score: 5/10). The results were conflicting in healthy older adults or no benefit was found for most of the performance, spatiotemporal, kinetic and angular related variables. Only one study (PEDro score: 6/10) showed improvements in stance phase duration (SMD=-1.92; 95% CI: -3.04, -0.81), swing phase duration (SMD=1.92; 95 CI: 0.81, 3.04), double support phase duration (SMD= -1.69; 95% CI: -2.76, -0.62) and step length (SMD=1.37; 95% CI: 0.36, 2.38) with large effect sizes. Conclusions: There is no strong evidence supporting the beneficial effect of using stretching to improve gait. Further randomized controlled trials are needed to understand the impact of stretching on human gait.

Anticipatory Postural Adjustments During Gait Initiation in Stroke Patients.

Prior to gait initiation (GI), anticipatory postural adjustments (GI-APA) are activated in order to reorganize posture, favorably for gait. In healthy subjects, the center of pressure (CoP) is displaced backward during GI-APA, bilaterally by reducing soleus activities and activating the tibialis anterior (TA) muscles, and laterally in the direction of the leading leg, by activating hip abductors. In post-stroke hemiparetic patients, TA, soleus and hip abductor activities are impaired on the paretic side. Reduction in non-affected triceps surae activity can also be observed. These may result in a decreased ability to execute GI-APA and to generate propulsion forces during step execution. A systematic review was conducted to provide an overview of the reorganization which occurs in GI-APA following stroke as well as of the most effective strategies for tailoring gait-rehabilitation to these patients. Sixteen articles were included, providing gait data from a total of 220 patients. Stroke patients show a decrease in the TA activity associated with difficulties in silencing soleus muscle activity of the paretic leg, a decreased CoP shift, lower propulsive anterior forces and a longer preparatory phase. Regarding possible gait-rehabilitation strategies, the selected studies show that initiating gait with the paretic leg provides poor balance. The use of the non-paretic as the leading leg can be a useful exercise to stimulate the paretic postural muscles.

Acute Effects of Whole-Body Vibration on the Postural Organization of Gait Initiation in Young Adults and Elderly: A Randomized Sham Intervention Study.

Whole-body vibration (WBV) is a training method that exposes the entire body to mechanical oscillations while standing erect or seated on a vibrating platform. This method is nowadays commonly used by clinicians to improve specific motor outcomes in various sub-populations such as elderly and young healthy adults, either sedentary or well-trained. The present study investigated the effects of acute WBV application on the balance control mechanisms during gait initiation (GI) in young healthy adults and elderly. It was hypothesized that the balance control mechanisms at play during gait initiation may compensate each other in case one or several components are perturbed following acute WBV application, so that postural stability and/or motor performance can be maintained or even improved. It is further hypothesized that this capacity of adaptation is altered with aging. Main results showed that the effects of acute WBV application on the GI postural organization depended on the age of participants. Specifically, a positive effect was observed on dynamic stability in the young adults, while no effect was observed in the elderly. An increased stance leg stiffness was also observed in the young adults only. The positive effect of WBV on dynamic stability was ascribed to an increase in the mediolateral amplitude of "anticipatory postural adjustments" following WBV application, which did overcompensate the potentially destabilizing effect of the increased stance leg stiffness. In elderly, no such anticipatory (nor corrective) postural adaptation was required since acute WBV application did not elicit any change in the stance leg stiffness. These results suggest that WBV application may be effective in improving dynamic stability but at the condition that participants are able to develop adaptive changes in balance control mechanisms, as did the young adults. Globally, these findings are thus in agreement with the hypothesis that balance control mechanisms are interdependent within the postural system, i.e., they may compensate each other in case one component (here the leg stiffness) is perturbed.

Long-Term Effects of Whole-Body Vibration on Human Gait: A Systematic Review and Meta-Analysis.

Background: Whole-body vibration is commonly used in physical medicine and neuro-rehabilitation as a clinical prevention and rehabilitation tool. The goal of this systematic review is to assess the long-term effects of whole-body vibration training on gait in different populations of patients. Methods: We conducted a literature search in PubMed, Science Direct, Springer, Sage and in study references for articles published prior to 7 December 2018. We used the keywords "vibration," "gait" and "walk" in combination with their Medical Subject Headings (MeSH) terms. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology was used. Only randomized controlled trials (RCT) published in English peer-reviewed journals were included. All patient categories were selected. The duration of Whole-Body Vibration (WBV) training had to be at least 4 weeks. The outcomes accepted could be clinical or biomechanical analysis. The selection procedure was conducted by two rehabilitation experts and disagreements were resolved by a third expert. Descriptive data regarding subjects, interventions, types of vibration, training parameters and main results on gait variables were collected and summarized in a descriptive table. The quality of selected studies was assessed using the PEDro scale. Statistical analysis was conducted to evaluate intergroup differences and changes after the WBV intervention compared to the pre-intervention status. The level of evidence was determined based on the results of meta-analysis (effect size), statistical heterogeneity (I 2) and methodological quality (PEDro scale). Results: A total of 859 studies were initially identified through databases with 46 articles meeting all of the inclusion criteria and thus selected for qualitative assessment. Twenty-five studies were included in meta-analysis for quantitative synthesis. In elderly subjects, small but significant improvements in the TUG test (SMD = -0.18; 95% CI: -0.32, -0.04) and the 10MWT (SMD = -0.28; 95% CI: -0.56, -0.01) were found in the WBV groups with a strong level of evidence (I 2 = 7%, p = 0.38 and I 2 = 22%, p = 0.28, respectively; PEDro scores ≥5/10). However, WBV failed to improve the 6MWT (SMD = 0.37; 95% CI: -0.03, 0.78) and the Tinetti gait scores (SMD = 0.04; 95% CI: -0.23, 0.31) in older adults. In stroke patients, significant improvement in the 6MWT (SMD = 0.33; 95% CI: 0.06, 0.59) was found after WBV interventions, with a strong level of evidence (I 2 = 0%, p = 0.58; PEDro score ≥5/10). On the other hand, there was no significant change in the TUG test despite a tendency toward improvement (SMD = -0.29; 95% CI: -0.60, 0.01). Results were inconsistent in COPD patients (I 2 = 66%, p = 0.03), leading to a conflicting level of evidence despite a significant improvement with a large effect size (SMD = 0.92; 95% CI: 0.32, 1.51) after WBV treatment. Similarly, the heterogeneous results in the TUG test (I 2 = 97%, p < 0.00001) in patients with knee osteoarthrosis make it impossible to draw a conclusion. Still, adding WBV treatment was effective in significantly improving the 6 MWT (SMD = 1.28; 95% CI: 0.57, 1.99), with a strong level of evidence (I 2 = 64%, p = 0.06; PEDro score ≥5/10). As in stroke, WBV failed to improve the results of the TUG test in multiple sclerosis patients (SMD = -0.11; 95% CI: -0.64, 0.43). Other outcomes presented moderate or even limited levels of evidence due to the lack of data in some studies or because only one RCT was identified in the review. Conclusions: WBV training can be effective for improving balance and gait speed in the elderly. The intervention is also effective in improving walking performance following stroke and in patients with knee osteoarthrosis. However, no effect was found on gait quality in the elderly or on balance in stroke and multiple sclerosis patients. The results are too heterogenous in COPD to conclude on the effect of the treatment. The results must be taken with caution due to the lack of data in some studies and the methodological heterogeneity in the interventions. Further research is needed to explore the possibility of establishing a standardized protocol targeting gait ability in a wide range of populations.

Coordination of pointing and stepping: do postural phenomena result from the juxtaposition of the dynamics of each task?

We questioned whether postural phenomena associated with the coordination of pointing and stepping resulted from the sole juxtaposition of the dynamics of each task during the overlapping time period ("juxtaposition hypothesis"). Nine subjects were involved in three experimental conditions: (1) "isolated stepping" (the stepping was performed alone), (2) "isolated pointing" (the pointing was performed alone), and (3) an "experimental sequence" (pointing and stepping were coordinated). Acceleration of centre of gravity (x''G) and displacement of centre of foot pressure (xP) were recorded using a force plate. Pointing acceleration was recorded using a wrist-strapped mono-axial accelerometer. The dynamics of a "theoretical sequence" were calculated by the linear summation of x''G and xP traces recorded in conditions (1) and (2). The juxtaposition hypothesis was tested by between-condition comparison of x''G and xP during the anticipatory postural adjustments of stepping, i.e., at time intervals when pointing was expected to most significantly influence stepping. Results showed that x''G and xP were higher (p<0.001 and 0.01, respectively) in the experimental than in the theoretical sequence. Also, when compared to isolated stepping, the experimental sequence was performed with a higher x''G (p<0.01) while xP remained unchanged (p>0.05). Altogether, our results suggest that the postural dynamics of pointing and stepping are not simply juxtaposed when both tasks are coordinated in a motor sequence. Conversely, the biomechanical consequences of the focal movement (pointing) on the mobility task (stepping) may be anticipated and integrated in the motor planning of quick stepping.

Influence of base of support size on arm pointing performance and associated anticipatory postural adjustments.

The current study was designed to test the effect of changing the base of support (BoS) size in the initial posture on the performance of a pointing task and the associated "anticipatory postural adjustments" (APAs). Subjects performed series of arm pointing tasks at maximal velocity, from five postures that differed by the antero-posterior (AP) distance between the heels. This distance was increased stepwise from 0 cm (P0 condition) to 40 cm (P40 condition). Kinetics data were collected with a large force-plate, and kinematics data of the pointing were collected with a bi-axial accelerometer (AP and vertical direction) fixed at the wrist. ANOVA showed that the amplitude and the efficiency of the APAs, as well as the performance of the pointing, all statistically increased from P0 to P40 (with 0.0001