Effect of Ischemia on the Length-Tension Diagram of Mammalian Skeletal Muscle

¹ From the Department of Physiology, State University of Iowa, Iowa City, Iowa

Ischemia was produced in the gastrocnemii of 13 rats by ligation and section of all soft tissue between knee and thigh. The contralateral muscle in each case served as a control. Isometric length-tension diagrams were obtained for both control and experimental muscles from 4 mm below resting length to 9 mm beyond resting length, stretch being imposed in 1-mm increments. In comparing the experimental and control length-tension diagrams, a 15% loss in active tension at resting length was observed in both the experimental and control muscles when the tension developed during an initial isometric tetanus was compared with tension developed at this length during the course of the length-tension diagram. The cause of this decrease is not certain but fatigue and changes in muscle extensibility were thought to play prominent roles. The active tension developed by the ischemic muscles was found to be less at all degrees of stretch, and in most instances this difference was significant. This tension loss in the ischemic muscles was not constant; plotting the difference between control and ischemic active tension revealed that from –4 mm to +2 mm of stretch the difference increased, while from +2 to +9 mm of stretch the tension loss decreased. This latter finding was further investigated by determining fatigue rates at selected degrees of stretch in ischemic and control muscles of 40 rats. These studies indicated that the ischemic muscles suffered a more rapid loss of active tension developed at degrees of stretch less than +2 mm but the control muscles had a more rapid active tension loss at lengths greater than +2 mm of stretch. An explanation for this is suggested. Development of contracture was thought to be the cause of the increase in the passive tension exhibited by the ischemic muscles.