Application of muscle sound to assess muscle tonus of the electrically stimulated muscle for FES

In a clinical use of functional electrical stimulation (FES), for example, it is often difficult to directly estimate muscular strength of the stimulated muscle. In this study, muscle sound has been applied for estimating muscle tonus, muscle strength, and tolerance for muscle fatigue. The relation between muscle sound and inner pressure of fascia, in addition to EMG and joint torque, has been examined. Based on autoregressive model analysis, the amplitude and peak frequency of the power-spectrum of muscle sound shows a better correlation to represent change of muscle strength in fatigued conditions, etc. It is concluded that muscle sound is an useful parameter to estimate muscle tonus, in addition to the popular electrophysiological signal EMG