Tension and Extensibility Changes in Muscle Suddenly Stretched During Tetanus

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Abstract
The rat triceps surae was prepared in situ for stimulation through the cut sciatic nerve and arranged for isometric recording. The average amt. of quick stretch for the 16 expts. reported is 6% of the muscle length at zero resting tension. Tension in excess of tetanic is induced by quick stretch during tetanus at lengths above and below the length required for development of maximal tetanic tension. It is suggested that the excess of tension in tetanized muscle is due primarily to passive resistance to stretch. This suggestion is supported by the observation that elastic elements of the resting muscle lengthen slowly for about 1 min. after quick stretch, losing about 40% of the tension induced by quick stretch while the muscle attains the new length-tension equilibrium. Extensibility is smaller in tetanized than in resting muscle at the same length, the difference in extensibility being large in short muscle and slight in extended muscle. Conversely, extensibility is greater in tetanized than in resting muscle at the same tension.