The relationship between myoelectrical properties and contraction intensity

The aim of this study was to investigate the relationship between muscle force and electromyography (EMG) amplitude of muscles around the ankle, elbow, and knee. Frequency analysis was also conducted. 31 healthy volunteers (24.55 ± 4.64 years, 1.72 ± 0.08 m, 72.08 ± 23.67 kg) participated in this study. Volunteers were injury-free and provided informed consent before taking part. Surface EMG (sEMG) electrodes were situated over a total of 15 muscles over three joints. The right ankle, elbow, and knee joints were fixed at their mid-range of motion while participants isometrically contracted antagonistic muscle pairs at 20, 40, 60, 80, and 100 per cent contraction intensity. Visual inspection and coefficient of determination (R2) of a linear trendline was used to determine linearity of the EMG-force relationship of each muscle tested. An R2 value ≥ 0.990 indicated a linear relationship, between 0.980 – 0.989 indicated a curvilinear relationship, and ≤ 0.979 indicated an elbow point relationship; Linear relationships: triceps brachii – lateral head (R2 0.995), triceps brachii – long head (R2 1.000), semitendinosus (R2 0.997), fibularis brevis (R2 0.999), fibularis longus (R2 0.992). Curvilinear relationships: biceps femoris (R2 0.987), soleus (R2 0.985), tibialis anterior (R2 0.983). Elbow point relationships: biceps brachii (R2 0.965), brachioradialis (R2 0.930), rectus femoris (R2 0.968), vastus lateralis (R2 0.971), vastus medialis (R2 0.967), gastrocnemius lateralis (R2 0.964), gastrocnemius medialis (R2 0.968). Based on these data muscle fibre type and joint angle appear to have the greatest influence on the EMG-force relationship. Future research using a wider range of joint angles would be recommended.