Neuromuscular impairments alter energetic cost landscape curvature and stride speed variability in post-stroke locomotion

Abstract

Neuromuscular impairments induce compensatory effects which alter the dynamics of human movement, but the mechanism linking specific impairments to post-stroke locomotion remains poorly understood. Here, we combine a predictive neuromusculoskeletal simulation framework with experimental gait observations in stroke survivors to test how two hemiparetic impairments, reduced muscle strength and increased baseline muscle activity, reshape the energetic cost landscape. We then evaluate whether impairment-dependent changes in the cost landscape curvature are associated with stride speed variability, which is experimentally observed to be higher after stroke. Using neuromusculoskeletal simulations, we show that increased paretic muscle activity reduces local curvature near the cost-minimized speed more than reduced paretic muscle strength and find that this predicts increases in stride speed variability observed in hemiparetic locomotion. These results support a mechanistic hypothesis that flatter cost landscapes reduce the relative cost of suboptimal behavior and, therefore, may contribute to increased motor variability after stroke. Author summaryMotor disorders, such as those caused by stroke, change the way humans walk and interact with the world, often reducing quality of life. Stroke affects millions of people each year and commonly causes unilateral motor impairment that requires substantial rehabilitation. In this study, we use simulations to understand how different impairments, specifically reduced muscle strength and increased muscle activity, alter movement behavior. By varying the severity of the impairment and the speed of walking, we show how different impairments lead to compensation strategies and influence sensitivity to speed fluctuations. These findings suggest that the energetic penalty incurred from suboptimal behavior changes with neuromuscular impairment and are predicted to contribute to increased variability after stroke.