Modulation of the thermoregulatory sweating response to mild hyperthermia during activation of the muscle metaboreflex in humans

1. To investigate the effect of the muscle metaboreflex on the thermoregula tory sweating response in humans, eight healthy male subjects performed sus tained isometric handgrip exercise in an environmental chamber (35 degrees C and 50% relative humidity) at 30 or 45% maximal voluntary contraction (MV C), at the end of which the blood circulation to the forearm was occluded f or 120 s. The environmental conditions were such as to produce sweating by increase in skin temperature without a marked change in oesophageal tempera ture. 2. During circulatory occlusion after handgrip exercise at 30% MVC for 120 s or at 45% MVC for 60 s, the sweating rate (SR) on the chest and forearm ( hairy regions), and the mean arterial blood pressure were significantly abo ve baseline values (P < 0.05). There were no changes from baseline values i n the oesophageal temperature, mean skin temperature, or SR on the palm (ha irless regions). 3. During the occlusion after handgrip exercise at 30% MVC for 60 s and dur ing the occlusion alone, none of the measured parameters differed from base line values. 4. It is concluded that, under mildly hyperthermic conditions, the thermore gulatory sweating response on the hairy regions is modulated by afferent si gnals from muscle metaboreceptors.