Acute effects of soleus EMG biofeedback training on tibiofemoral joint contact forces in young healthy adults

Articular cartilage health depends on optimal joint loading. Both insufficient and excessive loading may lead to catabolic effects in cartilage, which contribute to the development of osteoarthritis. This study investigates the effects of real-time biofeedback from soleus muscle activity on tibiofemoral joint loading during walking. Specifically, we examine whether increased soleus activation can reduce compressive forces on the medial tibiofemoral compartment and lower the external knee adduction moment (KAM), which may help manage osteoarthritis. Thirteen healthy young adults completed a baseline walking trial on an instrumented treadmill, followed by biofeedback trials, where they were instructed to modify soleus activation by +20 %, +40 %, and -20 % using real-time electromyography (EMG) feedback. Marker trajectories, ground reaction forces, and EMG from the soleus muscle were measured during each trial. KAM was estimated with inverse dynamics, and tibiofemoral joint contact forces (JCF) were computed with static optimization informed by soleus EMG in OpenSim. A linear mixed-effect model was used to analyze the relationship between soleus activation and tibiofemoral JCFs. Participants significantly increased soleus muscle activation in +20 % (Δ% = 20.27 ± 17.87, p = 0.043) and +40 % (Δ% = 25.17 ± 26.64, p = 0.037) biofeedback trials but could not decrease it. A negative correlation was found between soleus activation and total (slope: -0.172, p < 0.001), medial (slope: -0.077, p = 0.007), and lateral (slope: -0.266, p < 0.001) JCFs, with interindividual differences observed. While increasing soleus activation reduced JCFs, it also significantly increased KAM (slope: 0.358, p < 0.001). These findings show that soleus EMG biofeedback can be used to modify knee joint loading, but personalized approaches are needed.