Does heat production precede mechanical response in muscular contraction?

Abstract

A decision between two current theories of muscular contraction is provided by the proof that the heat production in a twitch begins before the mechanical response. In the skeletal muscle of the tortoise at 0 degrees C the heat production starts off at its maximum rate about 60 msec. after stimulation, while the tension cannot be detected before 90 to 100 msec. The heat of activation clearly precedes the mechanical response. The processes of contraction and relaxation in a tortoise's muscle occur at about one-tenth of the speed found in a frog's muscle at the same temperature. This should allow much greater accuracy in various investigations which are limited at present by the time taken in manipulation or recording.