Analysis of Fiber Proportion in Lower Limb Muscles Using Smoothed Pseudo Wigner-Ville Distribution

Muscle fiber composition is a key performance-determining factor in athletics. The proportion of slow-twitch fibers (STF) and fast-twitch fibers (FTF) may differ greatly in muscles due to factors such as genetics, training-induced changes, or underlying pathological conditions. This study investigates the fiber type proportion of lower limb muscles such as gastrocnemius lateralis (GL) and soleus (SOL) using surface electromyography. Isometric signals are recorded from both muscles during calf raise exercises. First and last one second epochs of the recorded signals correspond to non-fatigue (NF) and fatigue (F) zones respectively and are analyzed using smoothed pseudo Wigner-Ville distribution (SPWVD). Two features namely spectral entropy (SE) and peak frequency (PF) are extracted from both zones. During fatigue, SE shows a decline of 4.87% in GL and an increase of 3.7% in SOL. Similarly, a 65.3% decrease in PF in GL and 41% increase in SOL is observed. The reduction of SE and PF in GL may be due to the fatigue of FTF whereas the increment of these features in SOL might be due to the greater proportion of STF. The decrease of SE in GL reflects the reduction of complexity with fatigue. Hence, the extracted features are found effective in identifying the fiber type proportion of these muscles. The proposed approach can be used for fiber-type assessment in sports science and biomedicine.