Electromyogram patterns during plantarflexions at various angular velocities and knee angles in human triceps surae muscles

To investigate the influence of the various knee angles and ankle angular velocities on synergistic muscle activities, the surface electromyograms (EMG) were recorded from the triceps surae muscles, i.e. lateral gastrocnemius (LG), medial gastrocnemius (MG) and soleus (SOL) muscles. Six healthy young men performed ankle plantarflexions at three ankle angular velocities of 6, 30 and 60° · s−1 and three knee angles of 0, 30 and 60° (0° equalling full extension) under constant load (5% and 10% maximal voluntary contraction). At the fully-extended knee angle (0°), peak values of integrated EMG (peak iEMG) during ankle plantarflexions were significantly increased (P < 0.05) in MG and in LG, but significantly decreased (P < 0.05) in SOL with increasing angular velocity. On the other hand, although the patterns of variation of the peak iEMG in each muscle at flexed knee angles (30 and 60°) were very similar to the patterns seen at the fully-extended knee angle, there were no significant differences among angular velocities. During ankle plantarflexions at any of the angular velocities (6, 30 and 60° · s−1) the peak iEMG were significantly increased (P < 0.05) in SOL, but were significantly decreased (P < 0.05) in MG following increases in the knee angles. These results would suggest the possibility of selective recruitment of motor units in humans depending on the angular velocity; however, this behaviour would appear to be weakened by fixing at flexed knee angles which cause an inhibitory influence on gastrocnemius muscles and a facilitative influence on SOL.