Dynamic stability during split-belt walking and the relationship with step length symmetry.

INTRODUCTION: Walking instability is a contributor to falls and other undesired changes in walking performance. We investigated the effect of split-belt treadmill based perturbations on dynamic stability. Furthermore, we examined the relationships for dynamic stability and symmetry during unperturbed and perturbed walking. METHOD: Twenty healthy young adults completed unperturbed and perturbed walking conditions on a split-belt treadmill. The continuous perturbation involved moving the parallel belts at unequal speeds (1.5 m/s: 0.5 m/s). Margins of stability (MoS) and step length symmetry (SYM) were assessed. RESULTS: Stability and symmetry measures each decreased at the onset of the split walking perturbation. Only anterior-posterior (AP) MoS and SYM exhibited adaptive changes. Associations were found primarily for AP MoS with immediate changes in SYM at the onset of split walking, and over the duration of the split walking condition. DISCUSSION: Our findings suggest walking strategies were adapted to maintain dynamic stability when faced with a continuous perturbation. Additionally, dynamic stability was associated with symmetry during perturbed walking.

Locomotor adaptability in persons with unilateral transtibial amputation.

BACKGROUND: 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. OBJECTIVE: Determine if locomotor adaptability is impaired in persons with unilateral transtibial amputation (TTA). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.