Sweating responses during heat acclimation and moderate conditioning

Thermoregulatory Efficiency is Increased after Heat Acclimation in Tropical Natives

“…Interestingly, although the chest did not show an increase in sweat rate, its local skin temperature was reduced after the acclimation period, showing that there was more sweat evaporation but no increase in sweat production. We do not know by which mechanism the chest could increase its sweat evaporation without increasing local sweat rate; however, the chest is a very vasculated region with high blood flow (Shvartz et al, 1979) and, therefore, if the acclimation protocol employed in the present study increases chest blood flow, more heat would be transferred from the blood to the skin and from the latter to the environment through sweat, leading to more sweat evaporation for a given sweat rate. Therefore, it is possible that in the present study some skin sites increased sweating efficiency (e.g., the chest) and others reduced it (e.g., the thigh) so that whole-body sweating efficiency was maintained equally throughout the acclimation period but with increased skin wettedness and sweat evaporation.…”

“…We also observed a tendency for sweat redistribution towards the limbs: the sweat rate from the thigh, the forearm, and the arm showed a significant increase of 70%, 24%, and 35% (pϽ0.05 to all), respectively; on the other hand, the forehead and the chest did not show significant changes (11% and 12% increases, pϾ0.05 to both, respectively). Shvartz et al (1979) also used a constant work rate (50% V O 2max )in the heat (40°C and 48% rh) for eight days and found sweat redistribution towards the limbs: the increase in the arms and the thigh was higher than that of the chest. Regan et al (1996) used an environment similar to the present study and observed an increase in the forearm sweat rate in comparison to the forehead, while Patterson et al (2004) studied the effects of a period of humid HA on sweat redistribution and observed that although there was sweat redistribution, it did not follow the trunk-to-limb pattern.…”

“…Wind speed was set at 1.4Ϯ0.1 m · s Ϫ1 and was provided by an electric fan (Arno SL40, series MH, 120W, São Paulo, Brazil). This environment was chosen based on previous studies that were successful in inducing HA (Shvartz et al, 1979;Regan et al, 1996). The duration of the acclimation period was 13Ϯ0.4 days (range 12-15 days).…”

“…In addition to the increased whole-body sweat production, it has been noted that acclimation to exercise in the heat can change the local sweat rate pattern among body regions, that is, causes sweat redistribution (Patterson et al, 2004;Höfler, 1968;Shvartz et al, 1979). Fox et al (1964) were probably the first to notice that during HA, although whole-body sweat rate increased 50%, local arm sweat rate increased 300% possibly indicating sweat redistribution.…”

“…Fox et al (1964) were probably the first to notice that during HA, although whole-body sweat rate increased 50%, local arm sweat rate increased 300% possibly indicating sweat redistribution. However, a more comprehensive evaluation was provided by Höfler (1968) and Shvartz et al (1979) trunk in response to HA. The authors speculated that this response was because the limbs have a favorable area-to-mass ratio for heat dissipation and a higher sweat rate in the limbs would favor sweat evaporation and therefore thermal homeostasis.…”