Weight-bearing symmetry changes after asymmetric surface stiffness walking.

Stroke is a leading cause of adult disability in the United States, often presenting as hemiparesis. A priority in hemiparetic gait rehabilitation is the restoration of gait symmetry. While split belt treadmill training has shown promise in correcting spatial gait asymmetry, weight bearing and propulsion asymmetry remain resistant to improvement. As an alternative approach, we tested asymmetric surface stiffness walking to induce signatures of neuromotor adaptation relevant to correcting weight bearing and propulsion asymmetries in hemiparetic stroke. We hypothesized that a bout of asymmetric stiffness walking would elicit aftereffects in the form of asymmetries in weight bearing, propulsion, and plantar flexor activity. Twelve healthy young adults performed a 10-minute bout of asymmetric stiffness walking on an adjustable stiffness treadmill. We measured baseline and post-perturbation ground reaction forces (GRF) and spatio-temporal measures during 5-minute walking bouts on a dual-belt instrumented treadmill. After asymmetric surface stiffness walking, participants walked with increased vertical GRF and plantar flexor muscle excitations during push-off on the perturbed side relative to unperturbed. Participants also decreased their mid-stance vertical GRF and increased their peak braking GRF on the perturbed side relative to unperturbed. Counter to our hypothesis, they did not increase their propulsion GRF on the perturbed side. We conclude that asymmetric stiffness walking elicited a neuromotor adaptation towards a relative increase in push-off in the target limb, albeit primarily vertically aligned in our cohort of healthy young adults, and that gait adaptation to asymmetric stiffness walking should be investigated in individuals with push-off asymmetries. New & Noteworthy: Weight-bearing asymmetry in individuals with hemiparetic stroke is resistant to treatments that produce improvements in other gait function measures (e.g., spatio-temporal symmetry). We investigated a novel perturbed ground stiffness intervention applied by an adjustable surface stiffness treadmill and found significant aftereffects in vertical and braking ground reaction force peaks in healthy young adults, as well as increases in perturbed-side plantar flexor activity during push-off, indicating a strong potential for correcting persistent deficiencies in post-stroke gait.