Quantifying Segmental Contributions to Center-of-Mass Motion During Dynamic Continuous Support Surface Perturbations Using Simplified Estimation Models.

Investigating balance reactions following continuous, multidirectional, support surface perturbations is essential for improving our understanding of balance control in moving environments. Segmental motions are often incorporated into rapid balance reactions following external perturbations to balance, although the effects of these motions during complex, continuous perturbations have not been assessed. This study aimed to quantify the contributions of body segments (ie, trunk, head, upper extremity, and lower extremity) to the control of center-of-mass (COM) movement during continuous, multidirectional, support surface perturbations. Three-dimensional, whole-body kinematics were captured while 10 participants experienced 5 minutes of perturbations. Anteroposterior, mediolateral, and vertical COM position and velocity were calculated using a full-body model and 7 models with reduced numbers of segments, which were compared with the full-body model. With removal of body segments, errors relative to the full-body model increased, while relationship strength decreased. The inclusion of body segments appeared to affect COM measures, particularly COM velocity. Findings suggest that the body segments may provide a means of improving the control of COM motion, primarily its velocity, during continuous, multidirectional perturbations, and constitute a step toward improving our understanding of how the limbs contribute to balance control in moving environments.

Does Perturbation-Based Balance Training Improve Control of Reactive Stepping in Individuals with Chronic Stroke?

BACKGROUND: Although perturbation-based balance training (PBT) may be effective in improving reactive balance control and/or reducing fall risk in individuals with stroke, the characteristics of reactive balance responses that improve following PBT have not yet been identified. This study aimed to determine if reactive stepping characteristics and timing in response to support-surface perturbations improved to a greater extent following PBT, compared to traditional balance training. MATERIALS AND METHODS: This study represents a substudy of a multisite randomized controlled trial. Sixteen individuals with chronic stroke were randomly assigned to either perturbation-based or traditional balance training, and underwent 6-weeks of training as a part of the randomized controlled trial. Responses to support-surface perturbation were evaluated pre- and post-training, and 6-months post-training. Reactive stepping characteristics and timing were compared between sessions within each group, and between groups at post-training and 6-months post-training while controlling for each measure at the pre-training session. RESULTS: The frequency of extra steps in response to perturbations decreased from pre-training to post-training for the PBT group, but not for the control group. CONCLUSIONS: Improvements in reactive balance control were identified after PBT in individuals with chronic stroke. Findings provide insight into the mechanism by which PBT improves reactive balance control poststroke, and support the use of PBT in balance rehabilitation programs poststroke.

Interaction Between Thoracic Movement and Lumbar Spine Muscle Activation Patterns in Young Adults Asymptomatic for Low Back Pain: A Cross-Sectional Study.

OBJECTIVE: The purpose of this study was to investigate the interaction between thoracic movement and lumbar muscle co-contraction when the lumbar spine was held in a relatively neutral posture. METHODS: Thirty young adults, asymptomatic for back pain, performed 10 trials of upright standing, maximum trunk range of motion, and thoracic movement tasks while lumbar muscle activation was measured. Lumbar co-contraction was calculated, compared between tasks, and correlated to thoracic angles. RESULTS: Movement tasks typically exhibited greater co-contraction than upright standing. Co-contraction in the lumbar musculature was 67%, 45%, and 55% greater than upright standing for thoracic flex, thoracic bend, and thoracic twist, respectively. Generally, the thoracic movement task demonstrated greater co-contraction than the maximum task in the same direction. Co-contraction was also correlated to thoracic angles in each movement direction. CONCLUSION: Tasks with thoracic movement and a neutral lumbar spine posture resulted in increases in co-contraction within the lumbar musculature compared with quiet standing and maximum trunk range-of-motion tasks. Findings indicated an interaction between the 2 spine regions, suggesting that thoracic posture should be accounted for during the investigation of lumbar spine mechanics.

Balance Confidence Is Related to Features of Balance and Gait in Individuals with Chronic Stroke.

BACKGROUND: Reduced balance confidence is associated with impairments in features of balance and gait in individuals with subacute stroke. However, an understanding of these relationships in individuals at the chronic stage of stroke recovery is lacking. This study aimed to quantify the relationships between balance confidence and specific features of balance and gait in individuals with chronic stroke. METHODS: Participants completed a balance confidence questionnaire and clinical balance assessment (quiet standing, walking, and reactive stepping) at 6 months postdischarge from inpatient stroke rehabilitation. Regression analyses were performed using balance confidence as a predictor variable, and quiet standing, walking, and reactive stepping outcome measures as the dependent variables. RESULTS: Walking velocity was positively correlated with balance confidence, whereas mediolateral center of pressure excursion (quiet standing) and double support time, step width variability, and step time variability (walking) were negatively correlated with balance confidence. CONCLUSIONS: This study provides insight into the relationships between balance confidence and balance and gait measures in individuals with chronic stroke, suggesting that individuals with low balance confidence exhibited impaired control of quiet standing as well as walking characteristics associated with cautious gait strategies. Future work should identify the direction of these relationships to inform community-based stroke rehabilitation programs for individuals with chronic stroke, and determine the potential utility of incorporating interventions to improve balance confidence into these programs.

Does Perturbation Training Prevent Falls after Discharge from Stroke Rehabilitation? A Prospective Cohort Study with Historical Control.

BACKGROUND: Individuals with stroke fall frequently, and no exercise intervention has been shown to prevent falls post stroke. Perturbation-based balance training (PBT), which involves practicing reactions to instability, shows promise for preventing falls in older adults and individuals with Parkinson's disease. This study aimed to determine if PBT during inpatient stroke rehabilitation can prevent falls after discharge into the community. METHODS: Individuals with subacute stroke completed PBT as part of routine inpatient rehabilitation (n = 31). Participants reported falls experienced in daily life for up to 6 months post discharge. Fall rates were compared to a matched historical control group (HIS) who did not complete PBT during inpatient rehabilitation. RESULTS: Five of 31 PBT participants, compared to 15 of 31 HIS participants, reported at least 1 fall. PBT participants reported 10 falls (.84 falls per person per year) whereas HIS participants reported 31 falls (2.0 falls per person per year). When controlled for follow-up duration and motor impairment, fall rates were lower in the PBT group than the HIS group (rate ratio: .36 [.15, .79]; P = .016). CONCLUSIONS: These findings suggest that PBT is promising for reducing falls post stroke. While this was not a randomized controlled trial, this study may provide sufficient evidence for implementing PBT in stroke rehabilitation practice.

Perturbation training to promote safe independent mobility post-stroke: study protocol for a randomized controlled trial.

BACKGROUND: Falls are one of the most common medical complications post-stroke. Physical exercise, particularly exercise that challenges balance, reduces the risk of falls among healthy and frail older adults. However, exercise has not proven effective for preventing falls post-stroke. Falls ultimately occur when an individual fails to recover from a loss of balance. Thus, training to specifically improve reactive balance control could prevent falls. Perturbation training aims to improve reactive balance control by repeatedly exposing participants to postural perturbations. There is emerging evidence that perturbation training reduces fall rates among individuals with neurological conditions, such as Parkinson disease. The primary aim of this work is to determine if perturbation-based balance training can reduce occurrence of falls in daily life among individuals with chronic stroke. Secondary objectives are to determine the effect of perturbation training on balance confidence and activity restriction, and functional balance and mobility. METHODS/DESIGN: Individuals with chronic stroke will be recruited. Participants will be randomly assigned to one of two groups: 1) perturbation training, or 2) 'traditional' balance training. Perturbation training will involve both manual perturbations (e.g., a push or pull from a physiotherapist), and rapid voluntary movements to cause a loss of balance. Training will occur twice per week for 6 weeks. Participants will record falls and activity for 12 months following completion of the training program. Standardized clinical tools will be used to assess functional balance and mobility, and balance confidence before and after training. DISCUSSION: Falls are a significant problem for those with stroke. Despite the large body of work demonstrating effective interventions, such as exercise, for preventing falls in other populations, there is little evidence for interventions that prevent falls post-stroke. The proposed study will investigate a novel and promising intervention: perturbation training. If effective, this training has the potential to not only prevent falls, but to also improve safe independent mobility and engagement in daily activities for those with stroke. TRIAL REGISTRATION: Current Controlled Trials: ISRCTN05434601 .

Evaluation of the lumbar kinematic measures that most consistently characterize lumbar muscle activation patterns during trunk flexion: a cross-sectional study.

OBJECTIVE: The purpose of this study was to determine which kinematic measure most consistently determined onset and cessation of the flexion-relaxation response. METHODS: The study was a cross-sectional design in a laboratory setting in which 20 asymptomatic university-aged (19.8-33.3 years old) participants were tested. Muscle activation was measured for the lumbar erector spinae, and 3-dimensional motion was recorded. Flexion-relaxation onset and cessation occurrences were determined for 10 standing maximum voluntary flexion trials. The lumbar and trunk angles at both events were expressed as unnormalized (°) and normalized (%Max: percentage of maximum voluntary flexion) measures. Intraclass correlation coefficients and coefficients of variation were calculated to determine within- and between-participant reliability, respectively. RESULTS: Mean (SD) unnormalized flexion-relaxation angles ranged from 46.28° (11.63) (lumbar onset) to 108.10° (12.26) (trunk cessation), whereas normalized angles ranged from 71.31%Max (16.44) (trunk onset) to 94.83%Max (lumbar cessation). Intraclass correlation coefficients ranged from 0.905 (normalized lumbar, left side, onset) to 0.995 (unnormalized lumbar, both sides, cessation). Coefficients of variation ranged from 3.56% (normalized lumbar, right side, cessation) to 26.02% (unnormalized trunk, left side, onset). CONCLUSIONS: The data suggest that, for asymptomatic individuals, unnormalized and normalized lumbar kinematics most consistently characterized flexion-relaxation angles within and between participants, respectively. Lumbar measures may be preferential when the flexion-relaxation response is investigated in future clinical and biomechanical studies.

Differences in distal lower extremity tissue masses and mass ratios exist in athletes of sports involving repetitive impacts.

This study aimed to examine the effects of sex and sport on the tissue composition of the distal lower extremity of varsity athletes, in sports that involve repetitive-impact loading patterns. Fat mass, lean mass, bone mineral content and wobbling mass were predicted for the leg and leg + foot segments of varsity basketball, cross-country, soccer and volleyball athletes. The absolute masses were normalised to body mass, and also expressed relative to each other as ratios. Females and males differed on most normalised tissue masses and ratios by 11-101%. Characteristic differences were found in the normalised tissue masses across sports, with the lowest and highest values displayed by cross-country and volleyball (female)/basketball (male) athletes, respectively. Conversely, cross-country athletes had the highest wobbling mass:bone mineral content and lean mass:bone mineral content ratios for females by 10% and 16%, respectively. The differences between sports may be explained in part by different impact loading patterns characteristic of each sport. Tissue mass ratio differences between sports may suggest that the ratios of soft to rigid tissues are optimised by the body in response to typical loading patterns, and may therefore be useful in investigations of distal lower extremity injury mechanisms in athletes.

Quantification of the lumbar flexion-relaxation phenomenon: comparing outcomes of lumbar erector spinae and superficial lumbar multifidus in standing full trunk flexion and slumped sitting postures.

OBJECTIVE: The purpose of this study was to identify differences in flexion-relaxation outcomes in asymptomatic participants, with respect to both flexion-relaxation phenomenon (FRP) occurrence and spinal onset angles, as a function of posture and choice of muscle being examined. METHODS: This was a cross-sectional study in a laboratory setting. Thirty asymptomatic participants performed standing full trunk flexion and slumped sitting postures while activation levels of the lumbar erector spinae and superficial lumbar multifidus were monitored. Two thresholds were used to define whether FRP was present in each muscle and, if present, at what trunk flexion angle it occurred. These outcomes were compared descriptively between muscles and between postures. RESULTS: Most participants displayed FRP in both muscles during standing full flexion; occurrences were more variable in slumped sitting. On average, FRP during standing full flexion and slumped sitting occurred at approximately 80% and 52% of participants' maximum flexion value, respectively. Variability in the slumped sitting onset angles was greater than that in standing full flexion. CONCLUSION: Outcomes for FRP during standing full flexion in asymptomatic participants appeared to be more robust and were not affected by the choice of either lumbar erector spinae or superficial lumbar multifidus. Conversely, during slumped sitting, FRP occurrence varied substantially depending on choice of muscle, although onset angles were relatively consistent between muscles. Although the choice of one muscle over the other may be warranted, it may be prudent to examine both muscles during FRP investigations in sitting postures, in order to fully characterize the behavior and activation patterns of the lumbar musculature.

Head and arm positions that elicit maximal voluntary trunk range-of-motion measures.

Relationships have been shown between spinal motion and head and arm postures, yet there has been little standardization of the head and arm positions that elicit maximal voluntary spine angles during maximal trunk flexion, lateral bend, and axial twist. This study aimed to determine the head and arm positions that facilitated maximum voluntary range of motion in various spinal regions during these movements. Twenty-four individuals performed maximal movements in each plane with different combinations of head and arm positions (flexion and lateral bend: four combinations; axial twist: six combinations). Generally, greater angles were elicited for the upper spine regions when the head was moved in the direction of trunk motion, while the angles of the lower regions were either unaffected or greater when the head was kept in a neutral position. Arm positions also affected maximum spinal angles, in that angles were greatest when the arms were hanging to the floor (flexion), abducted to 90° (axial twist), and either hanging to the floor or crossed over the chest (lateral bend). These findings provide insight into the interplay between the spine and adjacent segments and constitute an initial attempt to develop standardized positions during maximum range-of-motion trials.

How do features of dynamic postural stability change with age during quiet standing, gait, and obstacle crossing?

Previous research has reported mixed findings regarding age-related changes in dynamic postural stability, quantified by margin of stability (MOS), during gait. However, age-related changes in MOS may be better elicited by tasks imposing greater challenges to the postural control system. Older adults' MOS during obstacle crossing, a destabilizing task, has previously been characterized, although studies comparing MOS during this task between younger and older adults remain sparse. This study investigated age-related changes in dynamic postural stability during quiet standing, gait, and obstacle crossing. Participants aged 20-30 (n = 20), 60-69 (n = 18), 70-79 (n = 15), and 80+ (n = 7; not analyzed statistically) years old performed these tasks while whole-body motion was tracked using motion capture. MOS in each direction was estimated throughout each trial, and integrals, transient ranges, and trial minima were extracted (as applicable). MOS time series were also ensemble averaged across age groups. No age-related differences were identified for quiet standing or gait. However, obstacle crossing metrics revealed greater stability (i.e., more positive MOS) and less instability (i.e., less negative MOS) in older adults, and reduced ranges during transients. These findings potentially arise from shorter step lengths, which may be the result of age-related physical declines; or may reflect a cautious strategy in older adults, which maximizes postural stability in the direction with the greatest consequences for foot-obstacle contact, as it changes throughout the task. This study supports the use of tasks imposing physical challenges and/or voluntary perturbations to study age-related changes in dynamic postural stability. Findings also contribute to our theoretical understanding of the time course of dynamic postural stability during functional tasks in relation to periods of transition in the base of support, and task-specific strategies adopted for obstacle crossing by older adults to maintain dynamic postural stability and mitigate fall risk.

Tissue mass ratios and the reporting of distal lower extremity injuries in varsity athletes at a Canadian University.

The purpose of this preliminary investigation was to determine the relative role of the distal lower extremity tissue masses of varsity athletes in predicting distal lower extremity injury sustained during a competitive season. One hundred male and female varsity athletes (basketball, volleyball, soccer, cross country) completed a questionnaire on general health, physiological, and psychosocial variables, during each sport's respective training camp. A series of anthropometric measurements were used as inputs to distal lower extremity tissue mass prediction equations to calculate lean mass, fat mass, bone mineral content and wobbling mass (lean mass + fat mass) and tissue mass ratios. Athletes were monitored throughout their respective seasons and were instructed to report any distal lower extremity injuries to a certified athletic therapist who was responsible for assessing and confirming the reports. Logistic regression analyses were performed to determine which variables significantly predicted distal lower extremity injury. Mean leg fat mass:bone mass (OR = 1.6, CI = 1.0 - 2.5), and competition surface (rubber OR = 8.5, CI = 1.5 - 47.7; artificial turf OR = 4.0, CI = 0.77 - 22.9) were identified as significant predictors of injury. Overall, tibia bone injuries were significantly associated with the ratio of fat mass:bone mineral content and the surface on which the athletes compete.

Evaluation of methods for the quantification of the flexion-relaxation phenomenon in the lumbar erector spinae muscles.

OBJECTIVES: There are various methods to quantify the flexion-relaxation phenomenon (FRP); however, there is little standardization. This study aimed to evaluate the performance of various quantification methods in terms of their ability to identify lumbar erector spinae flexion-relaxation during standing forward trunk flexion. METHODS: The study was a cross-sectional design in a laboratory setting. Lumbar erector spinae activation levels were measured in 12 male participants performing full trunk flexion movements. Electromyographical signals were assessed using 16 criteria within 4 quantification methods (visual, statistical, threshold, ratio), and the sensitivity of each was assessed relative to the benchmark criterion (visual inspection of raw electromyography data). RESULTS: Visual inspection and most of the threshold and ratio criteria displayed the highest sensitivity. On average (SD) across the 16 criteria, FRP was positively identified 21.6 (6.2) times of 24 data sets (12 participants, 2 muscles). The visual inspection criteria positively identified FRP in all 24 trials, whereas the statistical method did not identify FRP at all (P = .44 and P = .46 for the left and right sides, respectively). The threshold and ratio criteria positively identified FRP 23.2 (1.5) and 22.5 (3.7) times, on average, respectively. Results from criteria based on differences between upright and fully flexed muscle activation tended to be conservative in FRP identification. The methods were classified as reliable or nonreliable, based on their sensitivity when specific characteristics were evident in the electromyography signals. CONCLUSIONS: Although many of the criteria identified FRP with 100% sensitivity, others produced unrealistic results. The latter may be suitable for other experimental designs or may require reevaluation regarding their ability to identify FRP. Although visual inspection, threshold, or ratio methods performed well and may be appropriate for either biomechanical or clinical research, the threshold method provided the optimal trade-off between performance, consistency, and feasibility for these data.

Age affects the relationships between kinematics and postural stability during gait.

BACKGROUND: Past work has identified relationships between postural stability and joint kinematics during balance and sit-to-stand tasks. However, this work has not been extended to a thorough examination of these relationships during gait, and how these relationships change with age. An improved understanding of age-related changes in these relationships during gait is necessary to identify early predictors of gait impairments and implement targeted interventions to prevent functional decline in older adulthood. RESEARCH QUESTION: How does age affect relationships between time-varying signals representing joint/segment kinematics and postural stability during gait? METHODS: Three-dimensional, whole-body motion capture data from 48 participants (19 younger, 29 older) performing overground gait were used in this secondary analysis. Lower extremity joint angles, trunk segment angles, and margins of stability in the antero-posterior and mediolateral directions were subsequently derived. Pairings of angle and margin of stability signals were cross-correlated across the gait cycle. Metrics representing the strength of relationships were extracted from the cross-correlation functions and compared between groups. RESULTS: At the ankle, significant age-related differences were only identified in the mediolateral direction, with older adults' coefficients being of greater magnitude and more tightly clustered, relative to younger adults. Differences were observed in both directions at the hip, with an overall trend of greater-magnitude and more tightly clustered coefficients among younger adults. For the trunk, the groups exhibited coefficients of opposite signs in the antero-posterior direction. SIGNIFICANCE: While overall gait performance was similar between groups, age-related differences were identified in relationships between postural stability and kinematics, with stronger relationships at the hip and ankle for younger and older adults, respectively. Relationships between postural stability and kinematics may have potential as a marker for the early identification of gait impairment and/or dysfunction in older adulthood, and for quantifying the effectiveness of interventions to reduce gait impairment.

Reliability of unconventional centre of pressure measures of quiet standing balance in people with chronic stroke.

BACKGROUND: People with stroke often have asymmetric motor impairment. Investigating asymmetries in, and dynamic properties of, centre of pressure movement during quiet standing can inform how balance is controlled. RESEARCH QUESTION: What are the test-retest reliabilities of unconventional measures of quiet standing balance control in people with chronic stroke? METHODS: Twenty people with chronic stroke (>6 months post-stroke), who were able to stand for at least 30 s without support, were recruited. Participants completed two 30-second quiet standing trials in a standardized position. Unconventional measures of quiet standing balance control included: symmetry of variability in centre of pressure displacement and velocity, between-limb synchronization, and sample entropy. Root mean square of centre of pressure displacement and velocity in the antero-posterior and medio-lateral directions were also calculated. Intraclass correlation coefficients (ICCs) were used to determine test-retest reliability, and Bland-Altman plots were created to examine proportional biases. RESULTS: ICC3,2 were between 0.79 and 0.95 for all variables, indicating 'good' to 'excellent' reliability (>0.75). However, ICC3,1 for symmetry indices and between-limb synchronization were < 0.75. Bland-Altman plots revealed possible proportional biases for root mean square of medio-lateral centre of pressure displacement and velocity and between-limb synchronization, with larger between-trial differences for participants with worse values. SIGNIFICANCE: These findings suggest that centre of pressure measures extracted from a single 30-second quiet standing trial may have sufficient reliability for some research studies in chronic stroke. However, for clinical applications, the average of at least two trials may be required.

Leg tissue mass composition affects tibial acceleration response following impact.

To date, there has not been a direct examination of the effect that tissue composition (lean mass/muscle, fat mass, bone mineral content) differences between males and females has on how the tibia responds to impacts similar to those seen during running. To evaluate this, controlled heel impacts were imparted to 36 participants (6 M and 6 F in each of low, medium and high percent body fat [BF] groups) using a human pendulum. A skin-mounted accelerometer medial to the tibial tuberosity was used to determine the tibial response parameters (peak acceleration, acceleration slope and time to peak acceleration). There were no consistent effects of BF or specific tissue masses on the un-normalized tibial response parameters. However, females experienced 25% greater peak acceleration than males. When normalized to lean mass, wobbling mass, and bone mineral content, females experienced 50%, 62% and 70% greater peak acceleration, respectively, per gram of tissue than males. Higher magnitudes of lean mass and bone mass significantly contributed to decreased acceleration responses in general.

How does balance during functional tasks change across older adulthood?

BACKGROUND: Aging is associated with declining balance, which may increase fall risk and reduce independence. There is a paucity of work examining functional tasks (e.g., standing from a chair, lifting) related to fall risk. Additionally, many past studies have considered older adults as one age group, rather than viewing aging as a continuum across older adulthood. RESEARCH QUESTION: How are age and balance measures related in healthy, independently-dwelling older adults during functional tasks? METHODS: Thirty-eight older (60-89 years old) and 21 younger (18-30 years old) independently-dwelling adults performed quiet standing, sit-stand-sit, sit-stand-gait initiation, and lifting, while ground reaction forces and whole-body motion were measured. Variability of the net center of pressure displacement (root-mean-square; antero-posterior and mediolateral), and minimum margin of stability (anterior, posterior, mediolateral, and/or medial and lateral) were extracted. Regression analyses were used to identify relationships with age for both the full participant sample and the older adult cohort, accounting for sex and task characteristics. RESULTS: Age was significantly related to balance measures for both participant samples; net center of pressure root-mean-square and minimum margin of stability tended to increase and decrease with age, respectively. For older adults, significant relationships were primarily in the antero-posterior and mediolateral directions for sit-stand-gait initiation and sit-stand-sit, respectively. Relationships did not appear to be simply a function of differences in task performance with age. SIGNIFICANCE: Some evidence of balance declines during functional tasks was observed across older adulthood, including declines that did not appear in the full participant sample. However, further work with a more diverse older adult cohort will be required to confirm these results. Findings may contribute to the development of strategies for improving balance control and reducing fall risk in older adults, by identifying the balance measures most likely to decline across older adulthood as potential target tasks for interventions.

Improvements in balance reaction impairments following reactive balance training in individuals with sub-acute stroke: A prospective cohort study with historical control.

Background: Reactive balance training (RBT) has been previously found to reduce fall risk in individuals with sub-acute stroke; however, our understanding of the effects of RBT on specific balance impairments is lacking.Objective: To quantify changes in common balance reaction impairments in individuals with sub-acute stroke resulting from RBT, relative to traditional balance training, using a prospective cohort study design with a historical control group.Methods: Individuals with sub-acute stroke completed either RBT or traditional balance training as part of their routine care during physiotherapy in inpatient rehabilitation. Reactive balance control was assessed using lean-and-release perturbations pre-intervention, post-intervention, and 6-months post-intervention (follow-up). Individuals with impaired balance reactions (delayed foot-off times, slide steps, and/or a preference for stepping with the preferred limb) at the pre-intervention assessment were identified using video and force plate data. Outcome measures (foot-off times, frequency of trials with slide steps, and stepping with the preferred limb) from the RBT participants with impaired reactions were compared for each of the three assessments to the mean values for the participants with impaired reactions in the historical control group.Results: Improvements were observed in all outcome measures for the RBT participants between pre-intervention and post-intervention, and/or between post-intervention and follow-up. These improvements were generally equivalent to, if not better than, the improvements demonstrated by the historical control group.Conclusions: Findings further support the use of RBT for post-stroke inpatient rehabilitation, and provide insight into specific balance reaction impairments that are improved by RBT.

Lower limb muscle activity underlying temporal gait asymmetry post-stroke.

OBJECTIVE: Asymmetric walking after stroke is common, detrimental, and difficult to treat, but current knowledge of underlying physiological mechanisms is limited. This study investigated electromyographic (EMG) features of temporal gait asymmetry (TGA). METHODS: Participants post-stroke with or without TGA and control adults (n = 27, 8, and 9, respectively) performed self-paced overground gait trials. EMG, force plate, and motion capture data were collected. Lower limb muscle activity was compared across groups and sides (more/less affected). RESULTS: Significant group by side interaction effects were found: more affected plantarflexor stance activity ended early (p = .0006) and less affected dorsiflexor on/off time was delayed (p < .01) in persons with asymmetry compared to symmetric and normative controls. The TGA group exhibited fewer dorsiflexor bursts during swing (p = .0009). CONCLUSIONS: Temporal patterns of muscular activation, particularly about the ankle around the stance-to-swing transition period, are associated with TGA. The results may reflect specific impairments or compensations that affect locomotor coordination. SIGNIFICANCE: Neuromuscular underpinnings of spatiotemporal asymmetry have not been previously characterized. These novel findings may inform targeted therapeutic strategies to improve gait quality after stroke.

Characterizing slip-like responses during gait using an entire support surface perturbation: Comparisons to previously established slip methods.

BACKGROUND: The characteristics of experimentally induced slips (low-friction surfaces and non-motorized platforms) in laboratory settings are influenced by participant gait velocity, contact surface area, and level of friction between the foot and surface. However, motorized platforms that could account for these factors during slip-like paradigms have not been extensively used. RESEARCH QUESTION: How does slip-like perturbations evoked via a motorized platform change gait characteristics and postural stability during overground walking? METHODS: Ten healthy young adults performed 4 overground, self-paced walking trials, with the 4th trial including an unexpected forward support surface translation at heel-strike during steady state walking. Kinematic and kinetic data were collected, with step characteristics (time, distance, velocity) and postural stability calculated to compare between normal gait and slip-like trials. Slip foot characteristics were also determined. RESULTS: Peak slipping foot velocity variability was considerably smaller compared to previously reported low-friction and non-motorized perturbations. The centre of mass was shifted more posteriorly (thus in a less stable location) by the end of the platform acceleration phase compared to the same time point post-heel strike during normal gait trials. Participants successfully responded to every slip-like perturbation by significantly increasing step time, decreasing step distance, and decreasing step velocity. SIGNIFICANCE: Our results demonstrate the repeatability and consistency of a motorized support surface paradigm to induce slip-like perturbations. Furthermore, stability and step characteristic results confirm posterior shifts in stability and appropriate stepping responses, mimicking how participants would react if responding to a real world slip.