Comparison of stiffness of soleus and medial gastrocnemius muscles in cats.

Abstract

Tension changes were recorded during stretch of the contracting medial gastrocnemius (MG) and soleus (SOL) muscles in the same hindlimb of cats. The short-range stiffness of both MG and SOL was measured and separated into an active component in muscle fibers and a passive component in the tendon. The active component of the short-range stiffness was different for the 2 muscles and the difference could be accounted for in terms of numbers of sarcomeres per muscle fiber. The values of tendon compliance were similar for both muscles despite large differences in the geometrical arrangement of muscle fibers and tendons. With stretches comparable in amplitude to movements during locomotion, total stiffness reached a maximum value not at the peak, as expected, but during the rising phase of contraction, and the tension was largely determined by changes after the region of short-range stiffness was exceeded. The mechanical properties and geometry of the SOL and MG muscle are discussed with reference to their roles in posture and locomotion.