Locomotor adaptability in persons with unilateral transtibial amputation.
ABSTRACT: Locomotor adaptation enables walkers to modify strategies when faced with challenging walking conditions. While a variety of neurological injuries can impair locomotor adaptability, the effect of a lower extremity amputation on adaptability is poorly understood.Determine if locomotor adaptability is impaired in persons with unilateral transtibial amputation (TTA).The locomotor adaptability of 10 persons with a TTA and 8 persons without an amputation was tested while walking on a split-belt treadmill with the parallel belts running at the same (tied) or different (split) speeds. In the split condition, participants walked for 15 minutes with the respective belts moving at 0.5 m/s and 1.5 m/s. Temporal spatial symmetry measures were used to evaluate reactive accommodations to the perturbation, and the adaptive/de-adaptive response.Persons with TTA and the reference group of persons without amputation both demonstrated highly symmetric walking at baseline. During the split adaptation and tied post-adaptation walking both groups responded with the expected reactive accommodations. Likewise, adaptive and de-adaptive responses were observed. The magnitude and rate of change in the adaptive and de-adaptive responses were similar for persons with TTA and those without an amputation. Furthermore, adaptability was no different based on belt assignment for the prosthetic limb during split adaptation walking.Reactive changes and locomotor adaptation in response to a challenging and novel walking condition were similar in persons with TTA to those without an amputation. Results suggest persons with TTA have the capacity to modify locomotor strategies to meet the demands of most walking conditions despite challenges imposed by an amputation and use of a prosthetic limb.
Project description:Controlled trunk motion is crucial for balance and stability during walking. Persons with lower extremity amputation often exhibit abnormal trunk motion, yet underlying mechanisms are not well understood nor have optimal clinical interventions been established. The aim of this work was to characterize associations between altered lower extremity joint moments and altered trunk dynamics in persons with unilateral, transtibial amputation (TTA). Full-body gait data were collected from 10 persons with TTA and 10 uninjured persons walking overground (~1.4?m/s). Experimentally-measured trunk angular accelerations were decomposed into constituent accelerations caused by net joint moments throughout the body using an induced acceleration analysis. Results showed persons with TTA had similar ankle moment magnitude relative to uninjured persons (P?>?0.05), but greater trunk angular acceleration induced by the prosthetic ankle which acted to lean the trunk ipsilaterally (P?=?0.003). Additionally, persons with TTA had a reduced knee extensor moment relative to uninjured persons (P?<?0.001), resulting in lesser sagittal and frontal induced trunk angular accelerations (P?<?0.001). These data indicate kinetic compensations at joints other than the lumbar and hip contribute to altered trunk dynamics in persons with a unilateral TTA. Findings may inform development of new clinical strategies to modify problematic trunk motion.
Project description:Uneven walking surfaces pose challenges to balance, especially in individuals with lower extremity amputation. The purpose of this study was to determine if lateral stability of persons with unilateral transtibial amputation (TTA) is compromised when walking on a loose rock surface. Thirteen TTA and 15 healthy controls walked over level ground and over a loose rock surface at four controlled speeds. Dependent measures, including medial-lateral center of mass (COM) motion, step width variability, lateral arm swing velocity, and mean and variability of the minimum margins of stability (MOSmin), were compared between subject groups and across conditions. TTA had greater average MOSmin than Control subjects (p=0.018). TTA exhibited decreased MOSmin on their prosthetic limbs compared to their intact limbs (p=0.036), while Control subjects did not exhibit side to side differences. Both groups increased MOSmin with increasing walking speed (p?0.001). There was no difference in the average MOSmin between walking surfaces (p=0.724). However, the variability of MOSmin was greater on the rocks compared to level ground. Both subject groups increased step width, step width variability, COM range of motion and peak COM velocity when walking on the rock surface. TTA exhibited greater variability of both step width and MOSmin, which suggests that they made larger step-to-step corrective responses, more often, to achieve the same average result.
Project description:Previous research indicates the correlation structure of gait parameters (i.e., fractal dynamics) decreases with age. This decrease is suggested to reflect a reduced capacity for locomotor adaptation in older adults. The purpose of this study was to investigate potential differences between physical activity-matched young and older adults' fractal dynamics and gait adaptability during unperturbed and asymmetric walking, and to determine if fractal dynamics predict adaptive capacity. Fifteen young (28.9 ± 5.6 years, nine women) and 15 older (64.7 ± 2.7, nine women) adults with similar habitual physical activity levels walked at preferred speed, half of preferred speed, and asymmetrically whereby their dominant and non-dominant legs moved at preferred and half-preferred speed, respectively. Fractal correlations (scaling exponent ?) of stride times were assessed through detrended fluctuation analysis, and gait adaptation to asymmetric walking on the basis of lower limb relative phase. Both cohorts displayed similar fractal dynamics at preferred speed and asymmetric walking, while older adults exhibited greater ? during slow walking. Both groups exhibited comparable gait adaptation to split-belt walking based on analysis of lower limb relative phase. Fractal dynamics during preferred speed and asymmetric walking was moderately associated with gait adaptation in the young and older adult cohorts, respectively. In these activity-matched groups, there were no age-based reductions in fractal dynamics or gait adaptation, and fractal scaling ? was moderately associated with gait adaptation. These findings suggest that stride time fractal dynamics and gait adaptation may be preserved in older adults who habitually perform moderate intensity physical activity.
Project description:Locomotor adaptation is commonly studied using split-belt treadmill walking, in which each foot is placed on a belt moving at a different speed. As subjects adapt to split-belt walking, they reduce metabolic power, but the biomechanical mechanism behind this improved efficiency is unknown. Analyzing mechanical work performed by the legs and joints during split-belt adaptation could reveal this mechanism. Because ankle work in the step-to-step transition is more efficient than hip work, we hypothesized that control subjects would reduce hip work on the fast belt and increase ankle work during the step-to-step transition as they adapted. We further hypothesized that subjects with unilateral, trans-tibial amputation would instead increase propulsive work from their intact leg on the slow belt. Control subjects reduced hip work and shifted more ankle work to the step-to-step transition, supporting our hypothesis. Contrary to our second hypothesis, intact leg work, ankle work and hip work in amputees were unchanged during adaptation. Furthermore, all subjects increased collisional energy loss on the fast belt, but did not increase propulsive work. This was possible because subjects moved further backward during fast leg single support in late adaptation than in early adaptation, compensating by reducing backward movement in slow leg single support. In summary, subjects used two strategies to improve mechanical efficiency in split-belt walking adaptation: a CoM displacement strategy that allows for less forward propulsion on the fast belt; and, an ankle timing strategy that allows efficient ankle work in the step-to-step transition to increase while reducing inefficient hip work.
Project description:BACKGROUND AND PURPOSE:The optimal characteristics of learning to promote recovery of walking have yet to be defined for the poststroke population. We examined characteristics of task practice that limit or promote learning of a novel locomotor pattern. METHODS:Thirty-two persons with chronic hemiparesis were randomized to 2 conditions (constant and variable practice) and participated in two 15-minute sessions of split-belt treadmill walking. On day 1, subjects in the constant condition walked on the split-belt treadmill at a constant 2:1 speed ratio, while subjects in the variable condition walked on the split-belt treadmill at 3 different speed ratios. On day 2, both groups participated in 15 minutes of split-belt treadmill walking at the 2:1 speed ratio. Step length and limb phase symmetry metrics were measured to assess within-session learning (ie, adaptation) on day 1 and the ability to retain this new pattern of walking (ie, retention) on day 2. RESULTS:The amount of adaptation on day 1 did not differ depending upon practice structure (constant and variable) for step length or limb phase (a)symmetry. The magnitude of reduction in asymmetry from day 1 to day 2 did not differ between groups for step and limb phase (a)symmetry. DISCUSSION AND CONCLUSIONS:The results suggest that variable practice utilizing alternating belt speed ratios does not influence the ability of those with chronic stroke to adapt and retain a novel locomotor pattern. The effects of other forms of variable practice within other locomotor learning paradigms should be explored in those with chronic hemiparesis after stroke.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A257).
Project description:Optimizing rehabilitation strategies requires understanding the effects of contextual cues on adaptation learning. Prior studies have examined these effects on the specificity of split-belt walking adaptation, showing that contextual visual cues can be manipulated to modulate the magnitude, transfer, and washout of split-belt-induced learning in humans. Specifically, manipulating the availability of vision during training or testing phases of learning resulted in differences in adaptive mechanisms for temporal and spatial features of walking. However, multi-trial locomotor training has been rarely explored when using visual kinematic gait perturbations. In this study, we investigated multi-trial locomotor adaptation in ten healthy individuals while applying visual kinematic perturbations. Subjects were instructed to control a moving cursor, which represented the position of their heel, to follow a prescribed heel path profile displayed on a monitor. The perturbations were introduced by scaling all of the lower limb joint angles by a factor of 0.7 (i.e., a gain change), resulting in visual feedback errors between subjects' heel trajectories and the prescribed path profiles. Our findings suggest that, with practice, the subjects learned, albeit with different strategies, to reduce the tracking errors and showed faster response time in later trials. Moreover, the gait symmetry indices, in both the spatial and temporal domains, changed significantly during gait adaptation (<i>P</i> < 0.001). After-effects were present in the temporal gait symmetry index whens the visual perturbations were removed in the post-exposure period (<i>P</i> < 0.001), suggesting adaptation learning. These findings may have implications for developing novel gait rehabilitation interventions.
Project description:To investigate the adaptive locomotion mechanism in animals, a split-belt treadmill has been used, which has two parallel belts to produce left-right symmetric and asymmetric environments for walking. Spinal cats walking on the treadmill have suggested the contribution of the spinal cord and associated peripheral nervous system to the adaptive locomotion. Physiological studies have shown that phase resetting of locomotor commands involving a phase shift occurs depending on the types of sensory nerves and stimulation timing, and that muscle activation patterns during walking are represented by a linear combination of a few numbers of basic temporal patterns despite the complexity of the activation patterns. Our working hypothesis was that resetting the onset timings of basic temporal patterns based on the sensory information from the leg, especially extension of hip flexors, contributes to adaptive locomotion on the split-belt treadmill. Our hypothesis was examined by conducting forward dynamic simulations using a neuromusculoskeletal model of a rat walking on a split-belt treadmill with its hindlimbs and by comparing the simulated motions with the measured motions of rats.
Project description:INTRODUCTION:The ability to adapt dynamic balance to perturbations during gait deteriorates with age. To prevent age-related decline in adaptive control of dynamic balance, we must first understand how adaptive control of dynamic balance changes across the adult lifespan. We examined how adaptive control of the margin of stability (MoS) changes across the lifespan during perturbed and unperturbed walking on the split-belt treadmill. METHODS:Seventy-five healthy adults (age range, 18-80 yr) walked on an instrumented split-belt treadmill with and without split-belts. Linear regression analyses were performed for the mediolateral (ML) and anteroposterior (AP) MoS, step length, single support time, step width, double support time, and cadence during unperturbed and perturbed walking (split-belt perturbation), with age as predictor. RESULTS:Age did not significantly affect dynamic balance during unperturbed walking. However, during perturbed walking, the ML MoS of the leg on the slow belt increased across the lifespan due to a decrease in bilateral single support time. The AP MoS did not change with aging despite a decrease in step length. Double support time decreased and cadence increased across the lifespan when adapting to split-belt walking. Age did not affect step width. CONCLUSIONS:Aging affects the adaptive control of dynamic balance during perturbed but not unperturbed treadmill walking with controlled walking speed. The ML MoS increased across the lifespan, whereas bilateral single support times decreased. The lack of aging effects on unperturbed walking suggests that participants' balance should be challenged to assess aging effects during gait. The decrease in double support time and increase in cadence suggests that older adults use the increased cadence as a balance control strategy during challenging locomotor tasks.
Project description:BACKGROUND:Promising studies have shown that the gait symmetry of individuals with hemiparesis due to brain lesions, such as stroke, can improve through motor adaptation protocols forcing patients to use their affected limb more. However, little is known about how to facilitate this process. Here we asked if increasing propulsion demands during split-belt walking (i.e., legs moving at different speeds) leads to more motor adaptation and more symmetric gait in survivors of a stroke, as we previously observed in subjects without neurological disorders. METHODS:We investigated the effect of propulsion forces on locomotor adaptation during and after split-belt walking in the asymmetric motor system post-stroke. To test this, 12 subjects in the chronic phase post-stroke experienced a split-belt protocol in a flat and incline session so as to contrast the effects of two different propulsion demands. Step length asymmetry and propulsion forces were used to compare the motor behavior between the two sessions because these are clinically relevant measures that are altered by split-belt walking. RESULTS:The incline session resulted in more symmetric step lengths during late split-belt walking and larger after-effects following split-belt walking. In both testing sessions, subjects who have had a stroke adapted to regain speed and slope-specific leg orientations similarly to young, intact adults. Importantly, leg orientations, which were set by kinetic demands, during baseline walking were predictive of those achieved during split-belt walking, which in turn predicted each individual's post-adaptation behavior. These results are relevant because they provide evidence that survivors of a stroke can generate the leg-specific forces to walk more symmetrically, but also because we provide insight into factors underlying the therapeutic effect of split-belt walking. CONCLUSIONS:Individuals post-stroke at a chronic stage can adapt more during split-belt walking and have greater after-effects when propulsion demands are augmented by inclining the treadmill surface. Our results are promising since they suggest that increasing propulsion demands during paradigms that force patients to use their paretic side more could correct gait asymmetries post-stroke more effectively.
Project description:Induction of neural plasticity through motor learning has been demonstrated in animals and humans. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family of growth factors, is thought to play an integral role in modulation of central nervous system plasticity during learning and motor skill recovery. Thirty percent of humans possess a single-nucleotide polymorphism on the BDNF gene (Val66Met), which has been linked to decreased activity-dependent release of BDNF. Presence of the polymorphism has been associated with altered cortical activation, short-term plasticity and altered skill acquisition, and learning in healthy humans. The impact of the Val66Met polymorphism on motor learning post-stroke has not been explored. The purpose of this study was to examine the impact of the Val66Met polymorphism in learning of a novel locomotor task in subjects with chronic stroke. It was hypothesized that subjects with the polymorphism would have an altered rate and magnitude of adaptation to a novel locomotor walking paradigm (the split-belt treadmill), compared to those without the polymorphism. The rate of adaptation was evaluated as the reduction in gait asymmetry during the first 30 (early adaptation) and last 100 (late adaptation) strides. Twenty-seven individuals with chronic stroke participated in a single session of split-belt treadmill walking and tested for the polymorphism. Step length and limb phase were measured to assess adaptation of spatial and temporal parameters of walking. The rate of adaptation of step length asymmetry differed significantly between those with and without the polymorphism, while the amount of total adaptation did not. These results suggest that chronic stroke survivors, regardless of presence or absence of the polymorphism, are able to adapt their walking pattern over a period of trial-and-error practice; however, the presence of the polymorphism influences the rate at which this is achieved.