Recovery heat in muscle

It has been suggested (Sacks 1938, p. 222) “that the post-stimulation heat (in muscle) merely represents the inertia of the tissue in returning to the resting metabolic level after a burst activity.” It is true that the recovery heat after a single contraction, as ordinary observed, would not mean a very large increment in the resting metabolic rate, and that for single contractions it can be accurately measured only by assuming the resting heat rate as a constant base-line. Single contractions, however, have not provided the only, or indeed the strongest, evidence for the existence of the recovery heat; for example: (i) Hill (1928a, p. 188) showed that if oxygen is admitted to a muscle previously stimulated in nitrogen a large and prolonged heat production occurs: this experiment is regularly given as a class demonstration in this laboratory; (ii) Hill (1928a, p. 185) showed that during and after a long regular series of twiches the heat production in oxygen is considerably, not slighlty, greater than it is nitrogen; (iii) Bugnard (1934) examined the relation between total heat and initial heat during the steady state due to a regular series of shocks in oxygen. The recovery heat, as usual, was about equal to the initial heat. Its accumulated rate, however, was high, not low as after a single contraction. An amount of recovery heat equal to the initial heat occurred every half minute (the interval between shocks) throughtout the steady state. The heat rate during the interval between two shocks was about three times that of the resting muscle.