Abstract

The soleus (SOL) and extensor digitorum longus (EDL) muscles of the rat were studied in situ after 6 wk of disuse atrophy produced by hindlimb immobilization (IM). IM resulted in depressed peak twitch (Pt) and tentanic (Po) tension as well as a decreased rate of tension development and decline in the slowtwitch SOL. The fast-twitch EDL was affected to a lesser extent. Twitch duration, as meassured by contraction time and one-half relaxation time, was shortened in the SOL and prolonged in the EDL. In both the fast and slow muscles 30 min of electrical stimulation resulted in a significant decline in Po. Relative to the prefatigued Po, the atrophied and control muscles showed a similar fatigue pattern. This occurred in spite of lower ATP and glycogen concentrations and higher lactate levels in the atrophied muscles. Our results indicate significant impairmentofcontractile function following IM in fast and slow muscles with preferential alterations in the slow SOL. In addition, despite a lower resting capacity and an increased dependence on glycolysis, contractile properties of atrophied muscles differed little from control muscles in their pattern of response to 30 min of electrical stimulation. Verf.-Referat