Thermoregulatory changes in the cold induced by physical training in humans

It has previously been demonstrated that metabolic heat production (M) during cold exposure at rest was related to maximal oxygen uptake (VO2max). Consequently, an increase in VO2max could allow an increase M in the cold. The aim of the present study was therefore to test this hypothesis. Eight male volunteers undertook interval training (periods of 25% VO2max of 30-s duration and 110% VO2max of 60-s duration until exhaustion, five times a week over 8 weeks) to increase VO2max. Both before and after this physical training, they were subjected to a 10 degrees, 5 degrees and 1 degrees C 2-h cold air test in a climatic chamber. During the cold exposure, rectal temperature (Tre), tympanic temperature (Tty) mean skin temperature (Tsk) and M were measured as well as the time to onset of shivering (t) and body temperatures (Tre, Try and Tsk) at t. The results showed that physical training involved an increase in VO2max (14%-15%, P < 0.05). During the cold exposure, Tre was higher after training both at 10 degrees, 5 degrees and 1 degree C (P < 0.05) whereas Tty, TSk and M were not significantly changed. However, an increase in the sensitivity of the thermoregulatory system was attested by a decreased t at higher Tsk. These slight physiological changes found after training were not related to the increases in VO2max. In conclusion, this study demonstrated that interval training induced slight thermoregulatory changes unrelated to changes in VO2max and it suggested that M during cold exposure could be related mainly to the level of VO2max observed before training, since increases in VO2max did not modify M.