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

Summary The thermal responses of two healthy male subjects have been studied at the same mean skin temperature (T_sk) 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 (T_re) and oesophageal (T_oes) temperatures were higher in negative work and positive work with diathermy than normal control experiments. In resting experiments with diathermy, T_oes 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 (M_sw) was higher for a given M and T_sk than found for normal exercise, but in all three forms of work the relationship of M_sw to total heat production (H) was identical. During positive work with and without diathermy the differences in M_sw could be accounted for by using a previously developed model of relative sweating rate: %M_sw = – constant + T_re (or T_oes) + T_sk.In negative work, removal of the difference between predicted and observed %M_sw 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 M_sw 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.