Recovery of muscle functions in rats following prolonged movement restraint

Experiments were carried out to measure time and force parameters of isometric contractions and structural parameters of muscles of hind limbs of rats which were exposed to hypokinesia for 130 days and then were kept under surveillance for 3 months. During recovery certain functions of the contractile system returned to the normal. At the same time M. soleus displayed persistent changes that were indicative of atrophic developments. Unlike M. soleus where delayed contraction (due to an increase in the time of relaxation) was followed by losses in force, fast muscles (M. ext. digit. longus and M. plantaris) showed recovery of force parameters. They also exhibited delayed contraction due to an increase in the time of tension development and half-relaxation. These differences are associated with dissimilar function and structure of muscular fibers. On the whole, the pattern of recovery of the motor functions reflects responses to an increased load of the neuromuscular system of animals which are kept in large cages after prolonged hypokinesia.