Weight-bearing symmetry changes after asymmetric surface stiffness walking.

Mechanical gait asymmetry is a prevalent deficit in many forms of locomotion impairment. Although spatial gait asymmetry adaptations can be elicited with split-belt treadmill training, weight-bearing and propulsion asymmetry remain resistant to improvement. As an alternative approach, we tested asymmetric surface stiffness walking to induce neuromotor adaptation of weight-bearing and propulsion asymmetries. 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-min bout of asymmetric stiffness walking on an adjustable stiffness treadmill. We measured baseline and postperturbation ground reaction forces (GRFs) and spatiotemporal measures during 5-min walking bouts on a dual-belt instrumented treadmill. After asymmetric surface stiffness walking, participants exhibited 2.8% asymmetry in vertical GRF at push off, as well as increased plantarflexor muscle activity (20.7% GAS, 9.5% SOL) during push off on the perturbed side relative to the unperturbed. Participants also decreased their midstance vertical GRF (2.2%) and increased their peak braking GRF (6.8%) 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 toward 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., spatiotemporal 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 poststroke gait.