Skin Blood Flow in Athletes After Heat Exposure and Exercise Training

Abstract

Introduction: Exercise training has been shown to shift skin blood flow (SkBF) and sweating thresholds toward lower internal temperatures, and heat acclimation further lowered these thresholds (1). In athletes it is unclear as to whether SkBF to the active region after heat acclimation decreases, remains unchanged or increases during exhaustive competition in the heat. Using a laser-Doppler Blood Flowmeter (LDF) Hales (2) studied athletes with cycle exercise at moderate intensity in a high thermal condition and found relative upper limb SkBF drops near the end of exhaustive exercise. Traveling to international competitions is a way of life for today's top-level athletes. Often the athletes have to travel from a region of mild climate to a region of hot climate for competition, and have to deal with ambient heat and detraining problems. The concerns most coaches have are team traveling and the availability of a local training facility. It is of great interest to examine the extent of heat acclimation with vigorous exercise that could occur in a very short time period. The purpose of this study was to examine the effect of 5 daily sessions of vigorous cycle exercise in the heat on SkBF in athletes trained exclusively in an indoor facility. Methods: During off-season top-ranking male badminton (n = 7) and table-tennis (n = 7) players were recruited & randomly assigned into an experimental (EXP) or control (CON) group. The EXP trained on a cycle ergometer in a hot (37.9 °C) and the CON in a thermal neutral (24.2 °C) environment for 5 consecutive days. The duration of exercise was 25 min/day for day 1 and thereafter an increment of 5 min/day was added, and the intensity was increased from 10% below (day 1) to 5% above (day 5) their ventilatory threshold levels. The experimental protocol was approved by the Institutional Sports Science Research Committee, and informed consents were given by all participants. The following were measured before and after training using an incremental maximal cycle exercise (MXT) protocol: peak VO2, time to exhaustion (min), sweat volume (kg/m2/hr), O2-pulse, biceps (SkBFb) and quadriceps SkBF (SkBFq), mean skin temperature (Ts), and ear canal temperature (Te). SkBF were studied using a LDF (Vasamedics BPM2, MN), and a hardtip pencil probe placed on the surface of the skin, and were recorded at the same time as the skin and ear canal temperatures were taken. LDF values were recorded for 10 sec, and the peak and lowest values were averaged and reported as relative perfusion units. Two-way ANOVAs and Tukey post-hoc tests were used to analyze the data. All tests of statistical significance were set at p < .05 level. Results: The EXP subjects achieved heat acclimation (except sweat volume) in 5 days of repeated heat exposure and exercise. During the incremental MXT the EXP group exhibited: 1) increase in time to exhaustion, from 16.6 to 17.7 min in the hot (p < .05) and from 17.3 to 18.1 min in the thermoneutral conditions (p > .05), 2) lower heart rate in both conditions (p < .05), 3) increase in SkBFb during exercise in the thermoneutral condition (p < .05), 4) reduction in SkBFq during exercise in the hot (p < .05) and increase in SkBFq during exercise in the thermoneutral condition (p < .05), and 5) lower ear canal temperature during exercise in the hot condition (p < .05). These observations were not found in the CON group. Discussion: Two important adaptations were observed after heat acclimation: prolonged time to exhaustion and the ability to lower body temperature and heart rate during exhaustive exercise. After heat acclimation the %SkBFb during maximal cycle exercise in the hot condition was linearly related to workloads and was greater (p < .05) than before acclimation, suggesting that the increase in SkBF to the non-active limbs was needed to enhance the convective mechanism of heat exchange. Our results were inconsistent with Hales et al. (2), and agreed with those of Roberts et al. (1) who observed that after exercise training and heat acclimation during leg exercise forearm SkBF increases. They (1) also found that the threshold for skin vasodilation was shifted to lower internal temperatures relative to pre-acclimation levels. We conclude that reduction in SkBFq decreases blood perfusion to the working tissue, while increased SkBFb enhances convective heat exchange via the skin. The latter is beneficial to these athletes who compete indoors without the advantage of air-conditioning and convective cooling.