The role of movement errors in modifying spatiotemporal asymmetry post-stroke: a randomized clinical trial

Objective: Current rehabilitation to improve gait symmetry following stroke is based on one of two competing motor learning strategies: minimizing or augmenting symmetry errors. We sought to determine which of those motor learning strategies best improves overground spatiotemporal gait symmetry. Design: Randomized controlled trial. Setting: Rehabilitation research lab. Subjects: In all, 47 participants (59 ± 12 years old) with chronic hemiparesis post stroke and spatiotemporal gait asymmetry were randomized to error augmentation, error minimization, or conventional treadmill training (control) groups. Interventions: To augment or minimize asymmetry on a step-by-step basis, we developed a responsive, “closed-loop” control system, using a split-belt instrumented treadmill that continuously adjusted the difference in belt speeds to be proportional to the patient’s current asymmetry. Main measures: Overground spatiotemporal asymmetries and gait speeds were collected prior to and following 18 training sessions. Results: Step length asymmetry reduced after training, but stance time did not. There was no group × time interaction. Gait speed improved after training, but was not affected by type of asymmetry, or group. Of those who trained to modify step length asymmetry, there was a moderately strong linear relationship between the change in step length asymmetry and the change in gait speed. Conclusion: Augmenting errors was not superior to minimizing errors or providing only verbal feedback during conventional treadmill walking. Therefore, the use of verbal feedback to target spatiotemporal asymmetry, which was common to all participants, appears to be sufficient to reduce step length asymmetry. Alterations in stance time asymmetry were not elicited in any group

A neuromechanics-based powered ankle exoskeleton to assist walking post-stroke: a feasibility study

Background: In persons post-stroke, diminished ankle joint function can contribute to inadequate gait propulsion. To target paretic ankle impairments, we developed a neuromechanics-based powered ankle exoskeleton. Specifically, this exoskeleton supplies plantarflexion assistance that is proportional to the user’s paretic soleus electromyography (EMG) amplitude only during a phase of gait when the stance limb is subjected to an anteriorly directed ground reaction force (GRF). The purpose of this feasibility study was to examine the short-term effects of the powered ankle exoskeleton on the mechanics and energetics of gait. Methods: Five subjects with stroke walked with a powered ankle exoskeleton on the paretic limb for three 5 minute sessions. We analyzed the peak paretic ankle plantarflexion moment, paretic ankle positive work, symmetry of GRF propulsion impulse, and net metabolic power. Results: The exoskeleton increased the paretic plantarflexion moment by 16% during the powered walking trials relative to unassisted walking condition (p \u3c .05). Despite this enhanced paretic ankle moment, there was no significant increase in paretic ankle positive work, or changes in any other mechanical variables with the powered assistance. The exoskeleton assistance appeared to reduce the net metabolic power gradually with each 5 minute repetition, though no statistical significance was found. In three of the subjects, the paretic soleus activation during the propulsion phase of stance was reduced during the powered assistance compared to unassisted walking (35% reduction in the integrated EMG amplitude during the third powered session). Conclusions: This feasibility study demonstrated that the exoskeleton can enhance paretic ankle moment. Future studies with greater sample size and prolonged sessions are warranted to evaluate the effects of the powered ankle exoskeleton on overall gait outcomes in persons post-stroke

Central excitability contributes to supramaximal volitional contractions in human incomplete spinal cord injury

Individuals with a motor incomplete spinal cord injury (SCI) present clinically with partial control of muscles below the site of the injury, but experience profound weakness which can limit the ability to perform functional tasks such as walking. Interestingly, when individuals with an incomplete SCI are asked to maximally and repeatedly contract their quadriceps muscles, they demonstrate an increase in the peak force generated; individuals without SCI experience a decline in force, or ‘fatigue’. Following these repeated maximal efforts, reflex responses to electrical stimulation over the quadriceps muscle elicited amplified and prolonged, involuntary motor activity. Such responses were not observed prior to the maximal contractions, and were not observed in neurologically intact subjects. This finding suggests that increases in spinal excitability following these maximal efforts may enhance force generating capacity, and provides insight into possible novel therapeutic interventions to restore function following SCI

Balance impairment limits ability to increase walking speed in individuals with chronic stroke

Determine the relationship between balance impairments and the ability to increase walking speed (WS) on demand in individuals with chronic stroke

Individual limb mechanical analysis of gait following stroke

The step-to-step transition of walking requires significant mechanical and metabolic energy to redirect the center of mass. Inter-limb mechanical asymmetries during the step-to-step transition may increase overall energy demands and require compensation during single-support. The purpose of this study was to compare individual limb mechanical gait asymmetries during the step-to-step transitions, single-support and over a complete stride between two groups of individuals following stroke stratified by gait speed (≥0.8 m/s o

Prolonged Quadriceps Activity Following Imposed Hip Extension: A Neurophysiological Mechanism for Stiff-Knee Gait?

The biomechanical characteristics of stiff knee gait following neurological injury include decreased knee flexion velocity at toe-off, which may be due to exaggerated quadriceps activity. The neuromuscular mechanism underlying this abnormal activity is unclear, although hyperexcitable heteronymous reflexes may be a source of impaired coordination. The present study examines the contribution of reflex activity from hip flexors on knee extensors following stroke and its association with reduced swing-phase knee flexion during walking. Twelve individuals poststroke and six control subjects were positioned in supine on a Biodex dynamometer with the ankle and knee held in a static position. Isolated hip extension movements were imposed at 60, 90, and 120°/s through a 50° excursion to end-range hip extension. Reflexive responses of the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) were quantified during and after the imposed hip rotation. Gait analysis was also performed for all subjects in the stroke group. In subjects with stroke, imposed hip extension evoked a brief reflexive response in the quadriceps, followed by a heightened level of sustained activity. The initial response was velocity dependent and was larger in the stroke group than in the control group. In contrast, the prolonged response was not velocity dependent, was significantly greater in the VL and RF in subjects with stroke, and, importantly, was correlated to decreased swing-phase knee flexion. Hyperexcitable heteronymous connections from hip flexors to knee extensors appear to elicit prolonged quadriceps activity and may contribute to altered swing-phase knee kinematics following stroke

Biomechanical impairments and gait adaptations post-stroke: Multi-factorial associations

Understanding the potential causes of both reduced gait speed and compensatory frontal plane kinematics during walking in individuals post-stroke may be useful in developing effective rehabilitation strategies. Multiple linear regression analysis was used to select the combination of paretic limb impairments (frontal and sagittal plane hip strength, sagittal plane knee and ankle strength, and multi-joint knee/hip torque coupling) which best estimate gait speed and compensatory pelvic obliquity velocities at toeoff. Compensatory behaviors were defined as deviations from control subjects’ values. The gait speed model (n = 18; p = 0.003) revealed that greater hip abduction strength and multi-joint coupling of sagittal plane knee and frontal plane hip torques were associated with decreased velocity; however, gait speed was positively associated with paretic hip extension strength. Multi-joint coupling was the most influential predictor of gait speed. The second model (n = 15; p < 0.001) revealed that multi-joint coupling was associated with increased compensatory pelvic movement at toeoff; while hip extension and flexion and knee flexion strength were associated with reduced frontal plane pelvic compensations. In this case, hip extension strength had the greatest influence on pelvic behavior. The analyses revealed that different yet overlapping sets of single joint strength and multi-joint coupling measures were associated with gait speed and compensatory pelvic behavior during walking post-stroke. These findings provide insight regarding the potential impact of targeted rehabilitation paradigms on improving speed and compensatory kinematics following stroke

Arm swing magnitude and asymmetry during gait in the early stages of Parkinson's disease

The later stages of Parkinson's disease (PD) are characterized by altered gait patterns. Although decreased arm swing during gait is the most frequently reported motor dysfunction in individuals with PD, quantitative descriptions of gait in early PD have largely ignored upper extremity movements. This study was designed to perform a quantitative analysis of arm swing magnitude and asymmetry that might be useful in the assessment of early PD. Twelve individuals with early PD (in “off” state) and eight controls underwent gait analysis using an optically-based motion capture system. Participants were instructed to walk at normal and fast velocities, and then on heels (to minimize push-off). Arm swing was measured as the excursion of the wrist with respect to the pelvis. Arm swing magnitude for each arm, and inter-arm asymmetry, were compared between groups. Both groups had comparable gait velocities (p=0.61), and there was no significant difference between the groups in the magnitude of arm swing in all walking conditions for the arm that swung more (p=0.907) or less (p=0.080). Strikingly, the PD group showed significantly greater arm swing asymmetry (asymmetry angle: 13.9±7.9%) compared to the control group (asymmetry angle: 5.1±4.0%; p=0.003). Unlike arm swing magnitude, arm swing asymmetry unequivocally differs between people with early PD and controls. Such quantitative evaluation of arm swing, especially its asymmetry, may have utility for early and differential diagnosis, and for tracking disease progression in patients with later PD

Repeated Maximal Volitional Effort Contractions in Human Spinal Cord Injury: Initial Torque Increases and Reduced Fatigue

Substantial data indicate greater muscle fatigue in individuals with spinal cord injury (SCI) compared with healthy control subjects when tested by using electrical stimulation protocols. Few studies have investigated the extent of volitional fatigue in motor incomplete SCI

Quantifying mechanical and metabolic interdependence between speed and propulsive force during walking

Walking speed is a useful surrogate for health status across the population. Walking speed appears to be governed in part by interlimb coordination between propulsive (FP) and braking (FB) forces generated during step-to-step transitions and is simultaneously optimized to minimize metabolic cost. Of those forces, FP generated during push-off has received significantly more attention as a contributor to walking performance. Our goal was to first establish empirical relations between FP and walking speed and then to quantify their effects on metabolic cost in young adults. To specifically address any link between FP and walking speed, we used a self-paced treadmill controller and real-time biofeedback to independently prescribe walking speed or FP across a range of condition intensities. Walking with larger and smaller FP led to instinctively faster and slower walking speeds, respectively, with ~80% of variance in walking speed explained by FP. We also found that comparable changes in either FP or walking speed elicited predictable and relatively uniform changes in metabolic cost, together explaining ~53% of the variance in net metabolic power and ~14% of the variance in cost of transport. These results provide empirical data in support of an interdependent relation between FP and walking speed, building confidence that interventions designed to increase FP will translate to improved walking speed. Repeating this protocol in other populations may identify other relations that could inform the time course of gait decline due to age and disease