Distinguishing metabolic heat from condensation heat during muscle recovery.

When a thermopile is used to measure the heat production of isolated muscle, the muscle is surrounded by gas saturated with water vapour, initially in equilibrium with the muscle. After contraction, the osmolarity of the muscle is raised so that it is no longer in equilibrium with the gas around it, and condensation will occur. When artificial muscles 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 l). This temperature increase was greatly reduced by covering the artificial muscle with a Teflon film. Experiments on living muscle from the dogfish Scyliorhinus canicula 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 if it was covered. The Teflon covering did not diminish the muscle's contractile 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 largely be prevented so that only genuine metabolic recovery heat is produced.