More symmetrical gait after split-belt treadmill walking does not modify dynamic and postural balance in individuals post-stroke.

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.

Changes in lower limb muscle activity after walking on a split-belt treadmill in individuals post-stroke.

BACKGROUND: There is growing evidence that stroke survivors can adapt and improve step length symmetry in the context of split-belt treadmill (SBT) walking. However, less knowledge exists about the strategies involved for such adaptations. This study analyzed lower limb muscle activity in individuals post-stroke related to SBT-induced changes in step length. METHODS: Step length and surface EMG activity of six lower limb muscles were evaluated in individuals post-stroke (n=16) during (adaptation) and after (after-effects) walking at unequal belt speeds. RESULTS: During adaptation, significant increases in EMG activity were mainly found in proximal muscles (p⩽0.023), whereas after-effects were observed particularly in the distal muscles. The plantarflexor EMG increased after walking on the slow belt (p⩽0.023) and the dorsiflexors predominantly after walking on the fast belt (p⩽0.017) for both, non-paretic and paretic-fast conditions. Correlation analysis revealed that after-effects in step length were mainly associated with changes in distal paretic muscle activity (0.522⩽r⩽0.663) but not with functional deficits. Based on our results, SBT walking could be relevant for training individuals post-stroke who present shorter paretic step length combined with dorsiflexor weakness, or individuals with shorter nonparetic step length and plantarflexor weakness.

Relationships between lower body strength and the energy cost of treadmill walking in a cohort of healthy older adults: a cross-sectional analysis.

PURPOSE: Gait speed is associated with survival in older adults and it was suggested that an elevated energy cost of walking (Cw) is an important determinant of gait speed reduction. Thus far, little is known about the factors that contribute to a lower Cw but it was shown that lower body strength training could reduce the Cw. Therefore, the objective of this study was to investigate the relationship between lower body strength and the Cw in a cohort of healthy older adults. METHODS: A total of 48 participants were included in this study (70.7 ± 5.4 years). After a geriatric and a neuropsychological assessment, participants underwent a fitness testing protocol which included a maximal oxygen uptake test, assessment of the Cw at 4 km h-1 on a treadmill, an isokinetic maximal strength test for the ankle, knee and hip joints and a body composition assessment. Relationships between strength variables and the Cw were assessed with partial correlations and linear regression analyses. RESULTS: Hip extensors and hip flexors peak torque was significantly correlated with the Cw (r = -0.36 and -0.32, respectively; p < 0.05). A tendency towards significance was identified for the ankle plantar flexors (r = -0.25, p = 0.09). Hip extensors peak torque was the only significant neuromuscular parameter included in the linear regression analysis (p < 0.05). CONCLUSION: These results show that hip extensors are an important muscle group with regards to the Cw measured on a treadmill in this cohort of healthy older adults.

A more symmetrical gait after split-belt treadmill walking increases the effort in paretic plantar flexors in people post-stroke.

OBJECTIVE: To determine if the level of effort in paretic plantar flexors during gait could be a factor in explaining locomotor asymmetry. DESIGN: Cross-sectional study. SUBJECTS: Twenty individuals with chronic stroke (mean age 49.4 years (standard deviation 13.2). METHODS: Participants walked on a split-belt treadmill for 3 periods: baseline at self-selected speed; adaptation with the belt speed doubled on the non-paretic side; and post-adaptation at self-selected speed. Kinematic and kinetic data were recorded. The efforts were estimated with the muscular utilization ratio. Pearson correlation coefficients were used to assess the relationships between the paretic plantar flexor level of effort at baseline and changes in spatiotemporal gait parameters and joint moments after split-belt treadmill walking. In addition, in a subgroup of 12 asymmetrical individuals, paretic plantar flexor efforts were compared between periods (baseline (asymmetrical) and post-adaptation (symmetrical)) with paired Student's t-tests. RESULTS: Baseline level of effort in plantar flexors was negatively related to changes in paretic plantar flexion moments (r = -0.70; p = 0.001) and changes in non-paretic step length (r = -0.65; p = 0.003). A more symmetrical spatiotemporal gait increased the paretic plantar flexor effort from 73.7% to 86.6% (p = 0.007). CONCLUSION: A more symmetrical gait increases paretic plantar flexor efforts. Individuals post-stroke presenting high plantar flexor efforts when walking have limited muscle capacity to increase non-paretic step after split-belt walking.

Plantarflexor weakness is a determinant of kinetic asymmetry during gait in post-stroke individuals walking with high levels of effort.

BACKGROUND: Some studies in post-stroke individuals hypothesized that asymmetrical gait might be a strategy to symmetrize the effort in lower limb muscles. This study analyzed the asymmetry in the levels of effort, net joint moment during gait (walking moment) and maximal potential moment in the plantarflexors, hip flexors and extensors during gait. METHODS: Twenty post-stroke and 10 healthy individuals were assessed when walking at a comfortable speed on a treadmill. Their efforts were estimated bilaterally with a biomechanical approach (muscular utilization ratio) which is the walking moment relative to the muscle's maximal capability (maximal potential moment). Pearson correlations were used to assess the relationship between asymmetry in walking moment and maximal potential moment. FINDINGS: Healthy individuals presented symmetrical values of effort, walking moment and maximal potential moment for all muscle groups. Post-stroke individuals had asymmetrical walking moment in plantarflexion and hip extension. For the asymmetry in the levels of effort and maximal potential moment, they formed two subgroups; the low-effort subgroup presented symmetrical effort and their asymmetry in walking moment was not related to their asymmetry in maximal potential moment for plantarflexors (R = 0.44; P > 0.05). The high-effort subgroup presented asymmetrical effort (paretic side higher) and their asymmetry in walking moments was significantly associated to their asymmetry in maximal potential moment for plantarflexors and hip extensors (0.73≤R≤0.82; P<0.05). INTERPRETATION: Asymmetry in muscular strength is a determinant of walking moment asymmetry when the level of effort is high. These results might guide the type of locomotor training.

Multiple roads lead to Rome: combined high-intensity aerobic and strength training vs. gross motor activities leads to equivalent improvement in executive functions in a cohort of healthy older adults.

The effects of physical activity on cognition in older adults have been extensively investigated in the last decade. Different interventions such as aerobic, strength, and gross motor training programs have resulted in improvements in cognitive functions. However, the mechanisms underlying the relationship between physical activity and cognition are still poorly understood. Recently, it was shown that acute bouts of exercise resulted in reduced executive control at higher relative exercise intensities. Considering that aging is characterized by a reduction in potential energy ([Formula: see text] max - energy cost of walking), which leads to higher relative walking intensity for the same absolute speed, it could be argued that any intervention aimed at reducing the relative intensity of the locomotive task would improve executive control while walking. The objective of the present study was to determine the effects of a short-term (8 weeks) high-intensity strength and aerobic training program on executive functions (single and dual task) in a cohort of healthy older adults. Fifty-one participants were included and 47 (age, 70.7 ± 5.6) completed the study which compared the effects of three interventions: lower body strength + aerobic training (LBS-A), upper body strength + aerobic training (UBS-A), and gross motor activities (GMA). Training sessions were held 3 times every week. Both physical fitness (aerobic, neuromuscular, and body composition) and cognitive functions (RNG) during a dual task were assessed before and after the intervention. Even though the LBS-A and UBS-A interventions increased potential energy to a higher level (Effect size: LBS-A-moderate, UBS-A-small, GMA-trivial), all groups showed equivalent improvement in cognitive function, with inhibition being more sensitive to the intervention. These findings suggest that different exercise programs targeting physical fitness and/or gross motor skills may lead to equivalent improvement in cognition in healthy older adults. Such results call for further investigation of the multiple physiological pathways by which physical exercise can impact cognition in older adults.

Plantarflexion moment is a contributor to step length after-effect following walking on a split-belt treadmill in individuals with stroke and healthy individuals.

OBJECTIVE: To assess plantarflexion moment and hip joint moment after-effects following walking on a split-belt treadmill in healthy individuals and individuals post-stroke. DESIGN: Cross-sectional study. SUBJECTS: Ten healthy individuals (mean age 57.6 years (standard deviation; SD 17.2)) and twenty individuals post-stroke (mean age 49.3 years (SD 13.2)). METHODS: Participants walked on an instrumented split-belt treadmill under 3 gait periods: i) baseline (tied-belt); ii) adaptation (split-belt); and iii) post-adaptation (tied-belt). Participants post-stroke performed the protocol with the paretic and nonparetic leg on the faster belt when belts were split. Kinematic data were recorded with the Optotrak system and ground reaction forces were collected via the instrumented split-belt treadmill. RESULTS: In both groups, the fast plantarflexion moment was reduced and the slow plantarflexion moment was increased from mid-stance to toe-off in the post-adaptation period. Significant relationships were found between the plantarflexion moment and contralateral step length. CONCLUSION: Split-belt treadmills could be useful for restoring step length symmetry in individuals post-stroke who present with a longer paretic step length because the use of this type of intervention increases paretic plantarflexion moments. This intervention might be less recommended for individuals post-stroke with a shorter paretic step length because it reduces the paretic plantarflexion moment.

Perception threshold of locomotor symmetry while walking on a split-belt treadmill in healthy elderly individuals.

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.

Executive functions, physical fitness and mobility in well-functioning older adults.

The objective of this study was to examine the relationships between executive functions, physical fitness and mobility in well-functioning older adults. Forty-eight well functioning older adults (70.5±5.3years old; 20 men, 28 women) were included in this study. Two median splits were conducted based on each individual's performance for the 10MWT and TUG. Comparisons between groups of slower and faster individuals were made with regard to executive functions and physical fitness parameters. A correlational approach was used to assess the association between variables. Between groups comparisons revealed that faster individuals in mobility tests demonstrate better performances in measures of cognitive flexibility (0.68

Knee efforts and weight-bearing asymmetry during sit-to-stand tasks in individuals with hemiparesis and healthy controls.

The asymmetrical weight-bearing distribution of individuals with hemiparesis rising from a chair might be used to produce similar muscular efforts at the lower limbs. The aim of this study was to determine if individuals with hemiparesis have symmetrical levels of effort at the knee during spontaneous sit-to-stand transfers. Nineteen subjects with hemiparesis and 16 healthy controls participated. Their weight-bearing (WB) distribution during sit-to-stand was assessed with a force platform setup while the knee effort distribution was quantified using electromyographic (EMG) data normalized to maximal EMG values then expressed relative to the sum of the bilateral efforts. The healthy individuals presented symmetrical weight-bearing and knee effort distributions during the sit-to-stand transfer. The participants with hemiparesis, classified in three subgroups based on knee extensors' strength asymmetries (mild, moderate and severe), yielded different results. The mild group (n = 6) behaved like the controls, with almost symmetrical WB and knee efforts. The moderate group (n = 7) had similar WB and effort asymmetries while the severe group (n = 6) exhibited a WB distribution difference between sides but had almost symmetrical knee effort. These results for the severe group suggest that a control is exerted on the levels of effort when rising from a chair, which might be required when a certain threshold of effort is reached on the nonparetic side.

Perception of weight-bearing and effort distribution during sit-to-stand in individuals post-stroke.

The objectives were to assess whether individuals who are poststroke can rate their perceived knee effort distribution during sit-to-stand tasks in various foot positions, to quantify their errors of perception and to compare these to their errors in weight-bearing perception. Weight-bearing distribution was assessed in hemiparetic participants (N = 19) using a force platform. Electromyographic (EMG) data normalized to maximal EMG values were used to quantify knee effort distribution. The difference between participants' real weight bearing and knee effort and the perceived values rated on a visual analog scale defined their errors of weight-bearing and effort perception. The perception of effort and weight bearing, and the errors therein, were compared among the four foot positions. Participants perceived only the changes induced by the different foot positions on their weightbearing distribution, not on their knee effort distribution, and they made greater perception errors with the knee effort distribution than with the weight-bearing distribution.

Magnitude of force perception errors during static contractions of the knee extensors in healthy young and elderly individuals.

The accuracy of force perception during muscular contraction has not been studied extensively, despite its importance in rehabilitation and training. The purpose of this study was to quantify the errors made by healthy young and elderly individuals in their perceptions of force produced at the knee. Four different tasks were used to evaluate the perception of force and the effect of a sensory-motor reference and simultaneous contraction on the accuracy of perception. The absolute errors were similar between groups, with values of 11.9% to 16.3%, depending on the task. The raw perception errors were greater for high levels of force (>50% of the maximal voluntary contraction, or MVC), indicating an overestimation of the forces produced for both groups. At 70% MVC, the sensory-motor reference reduced raw perception errors, and the simultaneous contraction improved the accuracy of force production. Healthy young and elderly individuals had about the same capacity to judge the muscular force of their knee extensors. Therapists involved in the training of active elderly individuals should be aware that the accuracy of force perception is not perfect and that these clients have the same ability as young individuals to perceive their knee extension strength.

Perception of weight-bearing distribution during sit-to-stand task in healthy young and elderly individuals.

The first objective was to assess whether healthy individuals could accurately estimate their weight-bearing distribution in sit-to-stand transfers. The second was to evaluate the effect of age on weight-bearing perception. 16 young participants (11 women, 5 men; M age 29 yr., SD = 8.7) and 15 elderly participants (7 women, 8 men; M age 65 yr., SD = 3.8) were recruited. Verbal instructions and visual feedback referring to different percentages of weight-bearing distribution to execute were used to quantify weight-bearing perception in sit-to-stand tasks. For the feedback approach, the perception was assessed with a visual analog scale. For the verbal task, the weight-bearing distribution produced was assessed with force plates. Both young and elderly participants had good perception of weight-bearing distribution, with mean absolute errors of 6.4%. Moreover, their perceived and real weight-bearing distribution showed good agreement (ICC > or = .79).

Perception of weight-bearing distribution during sit-to-stand tasks in hemiparetic and healthy individuals.

BACKGROUND AND PURPOSE: It is unknown whether hemiparetic individuals are aware of their weight-bearing asymmetry during sit-to-stand tasks. This study compared the error between hemiparetic and healthy individuals' perception of weight-bearing and their actual weight-bearing distribution during the sit-to-stand task and analyzed the association between the knee extensor muscle strength and the weight-bearing distribution and perception. METHODS: Nineteen unilateral hemiparetic subjects and 15 healthy individuals participated in the study. They performed the sit-to-stand transfer on force platforms under different foot placements (spontaneous and symmetrical) and had to rate their perceived weight-bearing distribution at the lower limbs on a visual analog scale. The strength of the knee extensors was assessed with a Biodex dynamometer. RESULTS: The hemiparetic individuals presented greater weight-bearing asymmetry and errors of perception than the healthy individuals. Although no significant association was found between strength and weight-bearing perception, moderate associations were found between strength and weight-bearing distribution for both the spontaneous (r=0.75, P<0.01) and symmetrical (r=0.71, P<0.01) foot position conditions. CONCLUSIONS: This study revealed that individuals with hemiparesis after a stroke do not perceive themselves as asymmetrical when executing the sit-to-stand transfer and that the knee extensor strength is a factor linked to their weight-bearing asymmetry, not to their perception.