The effects of different levels of heat production induced by diathermy and eccentric work on thermoregulation during exercise at a given skin temperature.

The thermal responses of two healthy male subjects have been studied at the same mean skin temperature (Tsk) during negative work, positive work and positive work in which additional heating was induced by diathermy. The results showed that for a given metabolic heat production (M) rectal (Tre) and oesophageal (Toes) temperatures were higher in negative work and positive work with diathermy than normal control experiments. In resting experiments with diathermy, Toes rose to the same level as when an equal amount of heat was produced metabolically by exercise. In negative work and positive work with diathermy sweat loss (Msw) was higher for a given M and Tsk than found for normal exercise, but in all three forms of work the relationship of Msw to total heat production (H) was identical. During positive work with and without diathermy the differences in Msw could be accounted for by using a previously developed model of relative sweating rate: %Msw = -constant + alphaTre (or Toes) + betaTsk. In negative work, removal of the difference between predicted and observed %Msw required the inclusion of a further factor into the equation based on muscle temperature. The results suggest that the core temperature in exercise rises to meet the requirements of heat dissipation mainly by stimulating Msw and establishing a heat transfer gradient from core to periphery and is not necessarily or uniquely related to M or to the rate of working. The study underlines the usefulness of negative work and diathermy as physiological tools for the further understanding of thermoregulation during exercise.