Task dependent motor strategy of human triceps surae muscle.

Even though many investigators have analyzed the functional difference of the three heads of triceps surae in human, none of them succeeded to clarify the distinctive functional difference of those three muscles. The aim of this study was to investigate whether the integrated EMGs (IEMGs) of the triceps surae muscle, gastrocnemius and soleus, were task dependent. IEMGs of the medial head of the gastrocnemius (GM), lateral head of the gastrocnemius (GL), and soleus (SO) were investigated at three different knee joint angles, at four different duration of ramp contraction, with the generation of a single ongoing force, from 0 to the maximum voluntary contraction (MVC). Three-way ANOVAs for repeated measures were used to estimate differences in IEMG values in each of the GM, GL, and SO, taken at four different durations of ramp contraction (5, 10, 15 and 20 s), at three different knee joint angles (0 deg, 30 deg and 90 deg), across ankle plantar flexion levels of force (10, 20, 30, 40, 50, 60 and 70% MVC). According to three-way ANOVAs for repeated measures, IEMG of the GM muscle showed a first-order interaction between force and knee joint angle. In addition, IEMG of the GL muscle showed first-order interactions between the level of force and knee joint angle, and between the level of force and duration of ramp contraction. Furthermore, IEMG of the SO showed a main effect only on level of force. These results suggest that the each head of the triceps surae may work task dependently.