Surface EMG Analysis of Age-related Changes in Motor Unit Firing Rates of Triceps Surae During Isometric Plantar Flexion

The triceps surae muscle group has a very important role in supporting human posture and gait and is thus particularly interesting in the context of healthy aging and independent locomotion of older people. Despite plenty of research on age-related changes in human limb muscles, the underlying mechanisms are still not completely understood and there is no common consensus on the effects of aging in triceps surae muscles and their causes. Furthermore, a few recent research papers published results that seem to contradict the previous research and open new questions about the mechanisms of muscle adaptation to aging-related changes in human body.In this study, we used the decomposition of high-density surface electromyograms to analyze motor unit firing rates in triceps surae muscles of young and older subjects during isometric plantar flexion. When compared to the young subjects, the motor unit firing rates of older subjects were significantly higher in gastrocnemii muscles and significantly lower in soleus muscle. The presented results demonstrate that the age-related changes in triceps surae are muscle specific. They also demonstrate the feasibility of using high-density surface EMG to non-invasively track age-related changes in motor unit behavior.