FORCES IN GASTROCNEMIUS, SOLEUS, AND PLANTARIS TENDONS OF THE FREELY MOVING CAT

The purpose of this study was to gain an insight into the mechanisms o f force sharing among muscles in a functional group. Tendon force meas urements were obtained simultaneously from gastrocnemius, soleus, and plantaris muscles of 10 cats during a variety of different locomotor t asks using strain gauge based force transducers. In particular, tendon forces were measured for conditions where movement speed was altered systematically, and where movement speed was kept constant but externa l resistance to walking was varied systematically. The results show th at forces in the gastrocnemius and plantaris tendons increase with inc reasing intensities of movement, independent of intensity being altere d by varying speed or external resistance. In contrast, peak soleus fo rces, on an average, remained nearly the same for all conditions; howe ver, substantial modulations in soleus force were observed for consecu tive stride cycles. These results suggest that soleus forces are not l imited by peripheral (contractile) conditions but by central mechanism s and, further, that these central mechanisms depend on speed of movem ent and resistance to movement.