Enhanced skin blood flow response to hyperthermia after endurance training is mainly caused by plasma volume expansion in humans

 

Shigeki Ikegawa, Yoshi-ichiro Kamijo, Kazunobu Okazaki, Shizue Masuki, Yoshiyuki Okada, and Hiroshi Nose

Department of Sports Medical Sciences, Shinshu University Graduate School of Medicine, Matsumoto 390-8621, Japan.

 

We tested the hypothesis that enhanced skin blood flow (SkBF) response to hyperthermia after endurance training (ET) was mainly caused by plasma volume (PV) expansion in humans. Seven young men performed ET at 70% peak oxygen consumption rate (V_{O2 peak}) at 30 °C, 30 min/day, 5 days, while monitoring daily food intake. Before and after ET, we measured esophageal temperature (T_es) and forearm vascular conductance (FVC) during 30-min exercise at pre-training 65% V_{O2 peak} in the same environment as in ET in 2 conditions; normovolemia (Nor) and acute hypovolemia (Hypo) with a diuretic. ET lowered Tes threshold for an increase in FVC (TH_FVC) by 0.28 °C and elevated the sensitivity of an increase in FVC at a given rise in Tes (ΔFVC/ΔT_es) by 32% with ~10% PV expansion. In Hypo before ET, TH_FVC increased by 0.13 °C and ΔFVC/ΔT_es decreased by 5% compared with those in Nor before ET with ~10% PV loss. Similarly, in Hypo after ET, TH_FVC increased by 0.22 °C and ΔFVC/ΔT_es decreased by 38 % compared with those in Nor after ET with ~20% PV loss. We found that the effects of a given change in PV on TH_FVC and ΔFVC/ΔT_es after ET were not different from those by Hypo (P>0.05). Thus, enhanced SkBF response after ET might be mainly caused by PV expansion.

 

Key words: fluid, exercise, skin