Muscle coordination retraining inspired by musculoskeletal simulations: a study on reducing knee loading

Humans typically coordinate their muscles to meet movement objectives like minimizing energy expenditure. In the presence of pathology, new objectives gain importance, like reducing loading in an osteoarthritic joint, but people often do not change their muscle coordination patterns to meet these new objectives. Here we use musculoskeletal simulations to identify simple changes in coordination that can be taught by providing feedback of electromyographic activity to achieve a therapeutic goal--reducing joint loading. Our simulations predicted that changing the relative activation of the redundant ankle plantarflexors could reduce knee contact force during walking, but it was unclear whether humans could re-coordinate redundant muscles during a complex task like walking. With simple biofeedback of electromyographic activity, healthy individuals reduced the ratio of gastrocnemius to soleus muscle activation by 25{+/-}15% (p=0.004). The resulting "gastrocnemius avoidance" gait pattern reduced the late-stance peak of simulation-estimated knee contact force by 12{+/-}12% (p=0.029). Simulation-informed muscle coordination retraining could be a promising treatment for knee osteoarthritis and a powerful tool for optimizing coordination for a variety of rehabilitation and performance applications.