Rank order of peak amplitude of EMG between the three muscles of triceps surae during maximum isokinetic contractions.

Peak torque (PT) of maximum isokinetic plantar flexions was measured at 4 angular velocities (30, 60, 120 and 180 degrees/s) in 88 subjects. Simultaneous recordings of electromyograms (low-pass filtered and rectified) were obtained from the three heads of m. triceps surae. Subjects were clinically healthy subjects randomly chosen in age-groups 40-44, 50-54 and 60-64 years. The delays (in degrees) in range of motion (from maximum dorsiflexed position) of PT and of peak value of the low-pass filtered EMG-amplitudes (pEMG) were determined and ranked. pEMG of gastrocnemius medialis was reached before m. gastrocnemius lateralis which reached pEMG before m. soleus. At 30 degrees/s PT coincided with the pEMG of m. soleus, while at 120 and 180 degrees/s PT coincided with pEMGs of mm. gastrocnemii. The fixed rank order of pEMGs in the three muscles might be a reflexion of differences in the motor unit populations in the mm. gastrocnemii and m. soleus. The findings indicate that the relative roles of the three muscles, when torque-production is concerned, is dependent on angular velocity.