Weight-bearing symmetry changes after asymmetric surface stiffness walking

Mechanical gait asymmetry is a prevalent deficit in many forms of locomotion impairment. While 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-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 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 mid-stance 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 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.