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In immersive VR, a self-avatar that replicates the user’s movements and is viewed from a first-person perspective can substitute the real body. If the avatar’s movements are sufficiently synchronized with the user’s actual movements, the user can experience a sense of embodiment over the avatar. Recent studies have shown that discrepancies between the movements of the avatar and those of the user can be well tolerated while maintaining high levels of embodiment. The point at which a distortion is perceived (detection threshold) and its impact on the level of embodiment has not been studied in lower limb tasks such as gait. This study aimed to identify a detection threshold of gait asymmetry by unilaterally manipulating the step length of a self-avatar, and the effect of this detection on perceived embodiment. A real-time step length distortion model was developed, and a detection threshold between actual and avatar’s gait movement was assessed on thirty healthy participants. The step length was manipulated to introduce gait asymmetry (ascending condition) or start from a large asymmetry that was gradually decreased (descending). The results showed that, on average, the avatar’s step length could be increased by up to 12% before the participants detected the distortion. Furthermore, in the descending condition, they detected increases that were above 9%. The point of detection had no effect on the sense of embodiment as participants still reported being embodied in their avatars, even when they consciously detected the step length distortion. The sense of embodiment was closely correlated with the level of distortion; as distortion increased, embodiment decreased, and vice versa. For a given distortion level, embodiment was similar whether in the ascending or descending condition. This suggests that embodiment can be achieved even when the avatar’s spatial alignment initially differs from the participants’, provided that alignment is gradually restored. These results provide valuable insights into participants’ ability to tolerate movement discrepancies in embodied avatar experiences during gait in virtual environments, with potential applications in motor training and gait rehabilitation. [ABSTRACT FROM AUTHOR]

In virtual reality (VR), immersion can be created through synchronous visuomotor stimulations and enhanced by adding auditory or kinesthetic stimulations. Multiple patterned vibrations applied at the lower limbs might be a way to induce kinesthetic perception of gait motion that could be combined with VR stimulations to add the perception of self-motion. However, gait motion perception using multiple vibrations has not yet been evaluated. The objective of the study was to quantify the perception of gait motion while applying multiple, patterned vibrations to the lower limbs in healthy individuals. Twenty young healthy participants (25.1 ± 4.4 years) experienced multiple vibrations in 1-min trials. Stimulation consisted of a vibration pattern based on the sequence of muscle lengthening during a 2-s gait cycle. Stimulation was applied on participants in a standing position, under 11 experimental conditions controlling visual information (eyes open/closed), vibration frequency (40–80 Hz), and number and location of the joints stimulated (hips, knees, ankles isolated or combined two by two). Perception of gait motion was quantified for each condition using a 10-point visual analog scale (VAS, 0: "no perception", 10: "Perception of gait movements"). All participants except one achieved a score higher than 5/10 in at least one condition. Great variability was found for perception of gait motion within participants and conditions (VAS ranging from 0 to 9.6/10). Differences were found between conditions (p < 0.01), with higher mean and median scores in conditions that included knee vibration. Inducing gait motion perception is possible using multiple vibrations in healthy individuals. Stimulation of the knees seems to positively influence perception of gait motion. [ABSTRACT FROM AUTHOR]

Background: Previous studies have assessed the effects of perturbation training on balance after stroke. However, the perturbations were either applied while standing or were small in amplitude during gait, which is not representative of the most common fall conditions. The perturbations were also combined with other challenges such as progressive increases in treadmill speed.Objective: To determine the benefit of treadmill training with intense and unpredictable perturbations compared to treadmill walking-only training for dynamic balance and gait post-stroke.Methods: Twenty-one individuals post-stroke with reduced dynamic balance abilities, with or without a history of fall and ability to walk on a treadmill without external support or a walking aid for at least 1 min were allocated to either an unpredictable gait perturbation (Perturb) group or a walking-only (NonPerturb) group through covariate adaptive randomization. Nine training sessions were conducted over 3 weeks. NonPerturb participants only walked on the treadmill but were offered perturbation training after the control intervention. Pre- and post-training evaluations included balance and gait abilities, maximal knee strength, balance confidence and community integration. Six-week phone follow-ups were conducted for balance confidence and community integration. Satisfaction with perturbation training was also assessed.Results: With no baseline differences between groups (p > 0.075), perturbation training yielded large improvements in most variables in the Perturb (p < 0.05, Effect Size: ES > .46) group (n = 10) and the NonPerturb (p ≤ .089, ES > .45) group (n = 7 post-crossing), except for maximal strength (p > .23) in the NonPerturb group. Walking-only training in the NonPerturb group (n = 8, pre-crossing) mostly had no effect (p > .292, ES < .26), except on balance confidence (p = .063, ES = .46). The effects of the gait training were still present on balance confidence and community integration at follow-up. Satisfaction with the training program was high.Conclusion: Intense and unpredictable gait perturbations have the potential to be an efficient component of training to improve balance abilities and community integration in individuals with chronic stroke. Retrospective registration: ClinicalTrials.gov. March 18th, 2020. Identifier: NCT04314830. [ABSTRACT FROM AUTHOR]

Background: Braking forces absorbed by the leading paretic limb are greater than expected with regard to gait speed and not correlated with propulsive forces generated by the non-paretic limb in individuals with severe hemiparesis. Altered foot placement due to poor sensorimotor capacities may explain excessive braking forces.Research Question: The main objective of this study was to determine whether paretic foot placement was related to paretic braking forces in post-stroke individuals with various self-selected walking speeds and motor deficits.Methods: In this cross-sectional study, 34 chronic hemiparetic post-stroke individuals, divided into slow (< 0.7 m/s, n = 17) and faster (n = 17) subgroups, walked at their self-selected speed. Kinematic and kinetic parameters were measured. Braking impulses, peak braking forces, step characteristics and clinical status were compared between groups and limbs, and their correlations were tested using Pearson (or Spearman) correlation tests.Results: On the paretic side, braking impulses and step length were similar between groups despite the slower walking speed in the slow group. Paretic peak braking forces and step length were correlated in both groups (r = 0.5). Paretic braking forces were correlated with walking speed, foot placement ahead of the pelvis, trunk progression (TP) from non-paretic initial contact to paretic initial contact, and better motor function of the paretic limb for the faster walkers (0.6 < r < 0.7), but not for the slow walkers. Among the slow walkers, reduced TP ahead of the paretic foot was correlated with a higher paretic impulse (r =  -0.6).Significance: Better motor function likely helped the faster walkers to decelerate their center of mass appropriately relative to their walking speed. In the slow hemiparetic walkers, TP ahead of the paretic foot was perturbed. Clinicians should therefore consider vasti and plantar flexor muscle tone and activity that likely restrict TP ahead of the paretic foot and increase braking forces. [ABSTRACT FROM AUTHOR]

Gait initiation and termination are potentially challenging tasks for balance due to the transition from a quasi-static bipedal phase to a dynamic single-support phase. The purpose of this study was to compare the bipedal and single-support phases of gait initiation and termination in individuals with incomplete spinal cord injury (ISCI). Twelve individuals with ISCI were evaluated on the dynamic and postural components of balance using the stabilizing and destabilizing forces during gait initiation, termination and natural gait. Phase comparisons were made using non parametric tests. Visual inspection of the force profile of the factors explaining the forces was also conducted. Gait termination challenged more the postural control during the single-support phase than the bipedal phase for the dynamic component of the stabilizing/destabilizing forces model ( p = .002). For gait initiation, the most challenging phase varied with the components analyzed (single-support phase for the dynamic component, bipedal phase for the postural component) ( p ⩽ .008). The single support phase is more challenged during gait termination (both components) ( p ⩽ .015) while the bipedal phase is more challenged during gait initiation (dynamic components) ( p = .012). The stabilizing force and the speed of the center of mass on the one hand, and destabilizing force and the distance between the center of pressure and the base of support on the other hand, had a similar profile. The single-support phase of gait termination was the most challenging among all phases evaluated, being as challenging as the single-support phase of level natural gait. This phase should be targeted in rehabilitation in order to improve balance and decrease the risk of falling in this population. [ABSTRACT FROM AUTHOR]

Abstract: Background: Individuals with incomplete spinal cord injury need to be assessed in different environments. The objective of this study was to compare lower-limb power generation in subjects with spinal cord injury and healthy subjects while walking on an inclined pathway. Methods: Eleven subjects with spinal cord injury and eleven healthy subjects walked on an inclined pathway at their natural gait speed and at slow gait speed (healthy subjects only). Ground reaction forces were recorded by force plates embedded in the inclined pathway and a 3-D motion analysis system recorded lower-limb motions. Data analysis included gait cycle parameters and joint peak powers. Differences were identified by student t-tests. Findings: Gait cycle parameters were lower in spinal cord injury subjects compared to healthy subjects at natural speed but similar at slow gait speed. Subjects with spinal cord injury presented lower power at the ankle, knee and hip compared to healthy subjects at natural gait speed while only the power generation at push-off remained lower when the two groups performed at similar speed. Interpretation: The most important differences are associated with the fact that individuals with spinal cord injury walk at a slower speed, except for the ankle power generation. This study demonstrated that, even with a good motor recovery, distal deficits remain and may limit the ability to adapt to uphill and downhill walking. Inclined pathways are indicated to train patients with spinal cord injury. Clinicians should focus on the speed of uphill and downhill walking and on the use of plantar flexors. [Copyright &y& Elsevier]

Some hemiparetic patients walk asymmetrically. To better understand the mechanisms of this deficiency, the perception of locomotor symmetry was investigated in healthy elderly individuals. 16 participants (6 women, 10 men; M age = 70.9 yr., SD = 4.1) walked on a split-belt treadmill either at a self-selected or imposed gait speed. The speed of the two belts was initially similar (or different) and then gradually differed (or matched), so participants had to detect the point of perceived asymmetry (or symmetry). The results revealed that thresholds occurred when the belt speed ratios were .88 and .85. Initial gait speed did not affect the threshold. The parameter that correlated the most with belt speed asymmetry was stance time of the parameters measured. Future studies will investigate whether stroke affects gait symmetry judgments. [ABSTRACT FROM AUTHOR]

Abstract: Background: Walking with a load at the ankle during gait training is a simple way to resist lower limb movements to induce functional muscle strengthening. This study investigated the effects of walking with different loads attached above the paretic ankle on biomechanical gait parameters during over ground walking in post-stroke participants. Methods: Ten participants with moderate chronic hemiparesis were evaluated while walking over ground with three different loads (0.5, 1.0, and 1.5kg) attached above the paretic ankle. Gait speed, cadence, step lengths as well as hip and knee angular displacements, joint moments and power of the paretic limb were compared while walking with and without loads. Findings: Walking with a load led to an increased in gait speed (+0.03–0.05m/s), and in step length of the paretic leg (+5.6 to 9.4% step length, effect size=0.49–0.63), but not of the non-paretic leg. The proportion of the stance and swing phases did not change. Maximal joint moments (+20 to 48%, effect size=0.26–0.55) and power (+20 to 114%, effect size=0.30–0.57) increases varied across participants but were mostly affected in early stance at the hip and during the late swing phase at the knee. Mean angular displacement changes were less than 4°. Interpretation: Post-stroke participants are able to increase hip and knee power bursts to meet the increased mechanical demand of added loads attached to the paretic ankle, while preserving the basic pattern of walking. Further study is needed before using loading to functionally strengthen paretic muscles. [Copyright &y& Elsevier]

Muscle vibrations can induce motor responses and illusions of complex movements. However, inducing gait-like cyclical movements and illusions requires the application of multiple fast alternating vibrations to lower-limb muscles. The objectives were (1) to test the feasibility of delivering complex vibrations in a time-organized manner and (2) to illustrate the possibility of inducing alternate gait-in-place-like movements using these vibrations. Patterns of vibration, produced by 12 vibrators applied bilaterally on the flexor and extensor muscle groups of the lower limbs, were based on normal gait kinematics. We tested 1 s and 2 s cycle patterns of vibration. Vibrator responses were assessed using auto- and crosscorrelations and frequency analyses based on accelerometry measurements, and compared between patterns. High auto- (>0.8) and crosscorrelation (>0.6) coefficients demonstrated a good response by the vibrators to the control signal. Vibrations induced cyclical, low-amplitude stepping-in-place movements that mimicked alternate walking movements with both legs, with 1 s and 2 s cycle durations, in one nondisabled participant and one participant with American Spinal Injury Association Impairment Scale B spinal cord injury standing, relaxed, with body-weight support. Electromechanical vibrators can deliver complex cyclical vibrations and trigger gait-like lower-limb movements. These results warrant the application of these vibration patterns on individuals with sensorimotor impairments to test their potential in gait rehabilitation. [ABSTRACT FROM AUTHOR]

Intensity of balance exercises used to reduce fall risk is often poorly quantified. The study aimed to test whether balance difficulty can be rated during gait perturbations against balance difficulty during gait without perturbation, using the stabilizing/destabilizing forces. These forces represent the difficulty to maintain balance as the theoretical forces necessary to cancel body velocity and to set the body into an unstable posture, respectively. Ten healthy subjects walked on a split-belt treadmill, that also generated perturbations. Kinetic and kinematic data were collected during gait at comfortable and fast speeds without perturbation, and in five trials at comfortable speed with perturbations. Perturbations consisted of increasing or decreasing the speed of one belt to three different levels in each direction in a random order during the stance phase of 12 random steps per trial. The difficulty of maintaining balance was measured during the perturbation and the three following recovery steps. Compared to comfortable speed, higher stabilizing and lower destabilizing forces indicated higher balance difficulty during the perturbation step for faster-belt perturbations, and recovery steps for slower-belt perturbations. This was also associated with the center of mass shifted forward, and moving faster, and with the center of pressure closer to the forward limit of the base of support. Difficulty increased proportionally with the intensity of perturbation and was significantly higher for the more intense perturbations than at fast speed. Thus, the stabilizing/destabilizing forces seem adequate to evaluate balance difficulty during gait perturbations and could be used to determine the optimal difficulty for balance rehabilitation. [ABSTRACT FROM AUTHOR]

Abstract: Postural steadiness while standing is impaired in individuals with spinal cord injury (SCI) and could be potentially associated with increased reliance on visual inputs. The purpose of this study was to compare individuals with SCI and able-bodied participants on their use of visual inputs to maintain standing postural steadiness. Another aim was to quantify the association between visual contribution to achieve postural steadiness and a clinical balance scale. Individuals with SCI (n =15) and able-bodied controls (n =14) performed quasi-static stance, with eyes open or closed, on force plates for two 45s trials. Measurements of the centre of pressure (COP) included the mean value of the root mean square (RMS), mean COP velocity (MV) and COP sway area (SA). Individuals with SCI were also evaluated with the Mini-Balance Evaluation Systems Test (Mini BESTest), a clinical outcome measure of postural steadiness. Individuals with SCI were significantly less stable than able-bodied controls in both conditions. The Romberg ratios (eyes open/eyes closed) for COP MV and SA were significantly higher for individuals with SCI, indicating a higher contribution of visual inputs for postural steadiness in that population. Romberg ratios for RMS and SA were significantly associated with the Mini-BESTest. This study highlights the contribution of visual inputs in individuals with SCI when maintaining quasi-static standing posture. [Copyright &y& Elsevier]

Spontaneous gait is often asymmetrical in individuals post-stroke, despite their ability to walk more symmetrically on demand. Given the sensorimotor deficits in the paretic limb, this asymmetrical gait may facilitate balance maintenance. We used a split-belt walking protocol to alter gait asymmetry and determine the effects on dynamic and postural balance. Twenty individuals post-stroke walked on a split-belt treadmill. In two separate periods, the effects of walking with the non-paretic leg, and then the paretic one, on the faster belt on spatio-temporal symmetry and balance were compared before and after these perturbation periods. Kinematic and kinetic data were collected using a motion analysis system and an instrumented treadmill to determine symmetry ratios of spatiotemporal parameters and dynamic and postural balance. Balance, quantified by the concepts of stabilizing and destabilizing forces, was compared before and after split-belt walking for subgroups of participants who improved and worsened their symmetry. The side on the slow belt during split-belt walking, but not the changes in asymmetry, affected balance. Difficulty in maintaining balance was higher during stance phase of the leg that was on the slow belt and lower on the contralateral side after split-belt walking, mostly because the center of pressure was closer (higher difficulty) or further (lower difficulty) from the limit of the base of support, respectively. Changes in spatiotemporal parameters may be sought without additional alteration of balance during gait post-stroke. [ABSTRACT FROM AUTHOR]

It is still unknown to what extent overground walking with a WRE is equivalent to natural overground walking without a WRE. Hence, the interpretability of the 10-m (10MWT) and six-minute (6MWT) walk tests during overground walking with a WRE against reference values collected during natural overground walking without a WRE is challenging. This study aimed to 1) compare walking performance across three different overground walking conditions: natural walking without a WRE, walking with a WRE providing minimal assistance (active walking), and walking with a WRE proving complete assistance (passive walking) and 2) assess the association and the agreement between the 10MWT and the 6MWT during passive and active walking with a WRE. Seventeen healthy individuals who underwent basic locomotor training with a WRE performed the 10MWT (preferred and maximal speeds) and the 6MWT under the three conditions. For the 10MWT, the speed progressively and significantly decreased from natural walking without a WRE (preferred: 1.40±0.18m/s; maximal: 2.16±0.19m/s), to active walking with a WRE (preferred: 0.48±0.10m/s; maximal: 0.61±0.14m/s), and to passive walking with a WRE (preferred: 0.38±0.09m/s; maximal: 0.42±0.10m/s). For the 6MWT, total distances decreased from walking without a WRE (609±53.9m), to active walking with a WRE (196.6±42.6m), and to passive walking with a WRE (144.3±33.3m). The 10MWT and 6MWT provide distinct information and can't be used interchangeably to document speed only during active walking with the WRE. Speed and distance drastically decrease during active and, even more so, passive walking with the WRE in comparison to walking without a WRE. Selection of walking tests should depend on the level of assistance provided by the WRE. [ABSTRACT FROM AUTHOR]