Influence of forearm muscle metaboreceptor activation on sweating and cutaneous vascular responses during dynamic exercise

We examined whether the sustained activation of metaboreceptor in forearm during cycling exercise can modulate sweating and cutaneous vasodilation. On separate days, 12 young participants performed a 1.5-min isometric handgrip exercise at 40% maximal voluntary contraction followed by 1) 9-min forearm ischemia (Occlusion, to activate metaboreceptor) or 2) no ischemia (Control) in thermoneutral conditions (27°C, 50%) with mean skin temperature clamped at 34°C. Thirty seconds after the handgrip exercise, participants cycled for 13.5 min at 40% Vo_{2 max}. For Occlusion, forearm ischemia was maintained for 9 min followed by no ischemia thereafter. Local sweat rate (SR, ventilated capsule) and cutaneous vascular conductance (CVC, laser-Doppler perfusion units/mean arterial pressure) on the contralateral nonischemic arm as well as esophageal and skin temperatures were measured continuously. The period of ischemia in the early stages of exercise increased SR (+0.03 mg·cm^–2·min^–1, P < 0.05) but not CVC (P > 0.05) above Control levels. No differences were measured in the esophageal temperature at which onset of sweating (Control 37.19 ± 0.09 vs. Occlusion 37.07 ± 0.09°C) or CVC (Control 37.21 ± 0.08 vs. Occlusion 37.08 ± 0.10°C) as well as slopes for these responses (all P > 0.05). However, a greater elevation in SR occurred thereafter such that SR was significantly elevated at the end of the ischemic period relative to Control (0.37 ± 0.05 vs. 0.23 ± 0.05 mg·cm^–2·min^–1, respectively, P < 0.05) despite no differences in esophageal temperature. We conclude that the activation of forearm muscle metaboreceptor can modulate sweating, but not CVC, during cycling exercise without affecting the core temperature-SR relationship.

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