Heat acclimation improves cutaneous vascular function and sweating in trained cyclists

Abstract

The aim of this study was to explore heat acclimation effects on cutaneous vascular responses and sweating to local ACh infusions and local heating. We also sought to examine whether heat acclimation altered maximal skin blood flow. ACh (1, 10, and 100 mM) was infused in 20 highly trained cyclists via microdialysis before and after a 10-day heat acclimation program [two 45-min exercise bouts at 50% maximal O2 uptake (V̇o2max) in 40°C ( n = 12)] or control conditions [two 45-min exercise bouts at 50% V̇o2max in 13°C ( n = 8)]. Skin blood flow was monitored via laser-Doppler flowmetry (LDF), and cutaneous vascular conductance (CVC) was calculated as LDF ÷ mean arterial pressure. Sweat rate was measured by resistance hygrometry. Maximal brachial artery blood flow (forearm blood flow) was obtained by heating the contralateral forearm in a water spray device and measured by Doppler ultrasound. Heat acclimation increased %CVCmax responses to 1, 10, and 100 mM ACh (43.5 ± 3.4 vs. 52.6 ± 2.6% CVCmax, 67.7 ± 3.4 vs. 78.0 ± 3.0% CVCmax, and 81.0 ± 3.8 vs. 88.5 ± 1.1% CVCmax, respectively, all P < 0.05). Maximal forearm blood flow remained unchanged after heat acclimation (290.9 ± 12.7 vs. 269.9 ± 23.6 ml/min). The experimental group showed significant increases in sweating responses to 10 and 100 mM ACh (0.21 ± 0.03 vs. 0.31 ± 0.03 mg·cm−2·min−1 and 0.45 ± 0.05 vs. 0.67 ± 0.06 mg·cm−2·min−1, respectively, all P < 0.05), but not to 1 mM ACh (0.13 ± 0.02 vs. 0.18 ± 0.02 mg·cm−2·min−1, P = 0.147). No differences in any of the variables were found in the control group. Heat acclimation in highly trained subjects induced local adaptations within the skin microcirculation and sweat gland apparatus. Furthermore, maximal skin blood flow was not altered by heat acclimation, demonstrating that the observed changes were attributable to improvement in cutaneous vascular function and not to structural changes that limit maximal vasodilator capacity.

Ischaemic preconditioning does not alter the determinants of endurance running performance in the heat

“…It is possible that under heat stress, any reduction in skeletal muscle energy consumption were too small for these measures to detect or, from a haemodynamic perspective, skeletal muscle may not be sensitive to further increases in NO following IP, due to the apparently greater role of prostaglandins, relative to NO for inducing vasodilation (Kellogg et al 2005). Moreover, it is possible that blood vessels are already maximally dilated from heat stress (Lorenzo & Minson 2010).…”

Performance in the Heat—Physiological Factors of Importance for Hyperthermia‐Induced Fatigue

“…Regardless, 10 of 11 studies demonstrated that heat stress decreased VO 2max by a mean of -11%. Heat acclimatization status did not moderate the VO 2max decrease from temperate to hot conditions (160,270). Arngrimsson et al (15) were the only investigators to examine the impact of graded heat stress (in the same subjects) and found an inverse relationship (r = -0.77) between ambient temperature and VO 2max .…”

Assessment of Human Skin Microcirculation and Its Endothelial Function Using Laser Doppler Flowmetry

“…The discrimination between these two mechanisms is not possible as they overlap each other. Nevertheless, Lorenzo & Minson have shown that skin microcirculation also undergoes thermoadaptative changes as a part of acclimation to heat without eliciting reflexes engaged in exercise (Lorenzo & Minson, 2010). To do so, they trained subjects only at 50% of their V O2max , intensity that assumingly does not induce changes in the reflexes affecting exercise.…”