DISTINGUISHING METABOLIC HEAT FROM CONDENSATION HEAT DURING MUSCLE RECOVERY

When a thermopile is used to measure the heat production of isolated m uscle, the muscle is surrounded by gas saturated with water vapour, in itially in equilibrium with the muscle. After contraction, the osmolar ity of the muscle is raised so that it is no longer in equilibrium wit h the gas around it, and condensation will occur, When artificial musc les of known osmolarity were placed on a thermopile surrounded by gas in equilibrium with a solution of lower osmolarity, their temperature was found to be raised (by 102.7 mK osmol(-1) I). This temperature inc rease was greatly reduced by covering the artificial muscle with a Tef lon film. Experiments on living muscle from the dogfish Scyliorhinus c anicula showed that muscle temperature was higher 2 min after a series of 20 twitches at 3 Hz if the muscle was not covered by Teflon than i f it was covered. The Teflon covering did not diminish the muscle's co ntractile performance. We conclude that the condensation of water does contribute to the heat measured during the recovery period, but that when the muscle is covered by Teflon film condensation heat can largel y be prevented so that only genuine metabolic recovery heat is produce d.