Large Propulsion Demands Increase Locomotor Adaptation at the Expense of Step Length Symmetry

Abstract

There is an interest to identify factors facilitating locomotor adaptation induced by split-belt walking (i.e., legs moving at different speeds) because of its clinical potential. We hypothesized that augmenting braking forces, rather than propulsion forces, experienced at the feet would increase locomotor adaptation during and after split-belt walking. To test this, forces were modulated during split-belt walking with distinct slopes: incline (larger propulsion than braking), decline (larger braking than propulsion), and flat (similar propulsion and braking). Step length asymmetry was compared between groups because it is a clinically relevant measure robustly adapted on split-belt treadmills. Unexpectedly, the group with larger propulsion demands (i.e., the incline group) changed their gait the most during adaptation, reached their final adapted state more quickly, and had larger after-effects when the split-belt perturbation was removed. We also found that subjects who experienced larger disruptions of propulsion forces in early adaptation exhibited greater after-effects, which further highlights the catalytic role of propulsion forces on locomotor adaptation. The relevance of mechanical demands on shaping our movements was also indicated by the steady state split-belt behavior, during which each group recovered their baseline leg orientation to meet leg-specific force demands at the expense of step length symmetry. Notably, the flat group was nearly symmetric, whereas the incline and decline group overshot and undershot step length symmetry, respectively. Taken together, our results indicate that forces propelling the body facilitate gait changes during and after split-belt walking. Therefore, the particular propulsion demands to walk on a split-belt treadmill might explain the gait symmetry improvements in hemiparetic gait following split-belt training.

Cerebral Contribution to the Execution, But Not Recalibration, of Motor Commands in a Novel Walking Environment

“…altered environment and postadaptation behavior. This finding is consistent with previous work demonstrating that the extent to which subjects adapt their movements during split-belt walking does not predict their aftereffects (Sombric et al, 2019). Partial dissociation between steadystate and postadaptation behavior is further supported by the findings that aftereffects are not sensitive to manipulation of steady-state behavior through visual feedback (Wu et al, 2014;Long et al, 2016).…”

Cerebral contribution to the execution, but not recalibration, of motor commands in a novel walking environment

“…We found that stroke survivors exhibited intact recalibration of corrective responses, but impaired muscle patterns at steady state split-belt walking, suggesting partial dissociation between motor performance in the altered environment and post-adaptation behavior. This finding is consistent with previous work demonstrating that the extent to which subjects adapt their movements during split-belt walking does not predict their after-effects (Sombric et al, 2019). Partial dissociation between steady-state and post-adaptation behavior is further supported by the findings that aftereffects are not sensitive to manipulation of steady-state behavior through visual feedback (Wu et al, 2014;Long et al, 2016).…”

Using asymmetry to your advantage: learning to acquire and accept external assistance during prolonged split-belt walking

“…This does not 480 imply that adaptation cannot occur rapidly with other experimental manipulations. There is evidence that 481 people adopt longer steps with the leg on the fast belt when walking on an inclined split-belt treadmill for 482 10 minutes (Sombric et al, 2019) or when adapting to belt speeds close to running for five minutes 483 (Yokoyama et al, 2018). Given that these studies did not calculate mechanical work, and we do not know 484 what the energetically optimal solution for the above studies would be, we cannot speculate if the rate of 485 adaptation toward the energy optimal behavior occurred more rapidly than in the current study.…”