The effects of pre-cooling on skin blood flow during exercise in the heat and subsequent performance

Abstract

Introduction: Exercise disturbs the homeostatic state of the human body causing an increase in heat production which is exacerbated in hyperthermic conditions. Ice vest cooling both before and during exercise has been shown to alleviate thermal strain and attenuate a rise in core temperature. It has been proposed that skin blood flow may be significantly reduced during cooling and blunted during subsequent exercise with increases in skin blood flow, due to exercise, cooling the perfusing blood which abate a rise in core temperature on return.
Aims: The purpose of this study was to determine whether pre-cooling (COOL), with an ice vest, reduces skin blood flow compared to a no cooling control (CON), and whether subsequent exercise and 3-km performance times in the heat are improved on a cycle ergometer. A secondary aim was to determine the effects of ice vest cooling on the physiological responses during seated rest and heat exposure to observe the responses of cooling without exercise metabolic heat production. 
Methods: Eight male participants volunteered to take part in the study. The mean (±SD) age, height, weight and maximal oxygen uptake (V̇O_2max) were; 24.5 ±5.0 years, 178.7 ±2.6 cm, 77.5 ±13.7 kg, and 43.4 ±8.6 ml.min.^-1kg.^-1, respectively. Ice vest cooling was applied in cool conditions for 20 min prior to exercise and seated rest in the heat (35.4 ±0.4°C, 26.3 ±4.1% RH). The intermittent exercise protocol was carried out on a cycle ergometer and consisted of nine × five min bouts of exercise consisting of; 2 min 30 seconds at 40% V̇O_2max, 1 min 30 seconds at 60% V̇O_2max, 30 seconds at 100% V̇O_2max, and 30 seconds of unloaded cycling at a cadence of 70 rev.min.^-1. Following this, a three kilometre performance trial (PT) was performed at a resistance set at 60% V̇O_2max with the instruction to complete the distance as fast as possible. Seated rest in the heat was undertake for 45 min. Rectal (T_rec) and aural (T_aur) temperature, mean skin temperature (T_ms), skin blood flow (SkBF), heart rate (HR), oxygen uptake (VO₂), blood lactate ([BLa]), perceived exertion (RPE), thermal strain (RPTS), and profile of mood states (POMS) were recorded throughout the trial. A two-way analysis of analysis of variance (ANOVA) with repeated measures on both factors (trial × time) was used to determine statistical differences. 
Results: SkBF was not significantly affected by ice vest cooling at any time point during cooling, seated rest in the heat or exercise trials (P>0.05). No significant interactions were observed during cooling for both T_aur and T_rec (P>0.05). T_aur throughout the seated rest trial (P<0.01) remained significantly lower following a cooling period compared to CON. T_aur was significantly lower from 5-25 min of exercise (P<0.01) following a cooling period compared to CON. T_rec was significantly lower at the end of the seated rest trial in the heat following a cooling period compared to CON (P<0.01) but did not differ at any time point during the exercise trial (P>0.05). T_ms and RPTS was significantly lower during cooling compared to CON (P<0.01) but did not differ thereafter. No significant difference was observed for performance between trials. 
Discussion: It appears that the attenuated rise in core temperature is not due to a blunted rise in SkBF during exercise. It is possible that following cooling there is a significant heat sink created at the skin which cools the perfusing blood in the cutaneous circulation which would cool the core on return. Despite this, there were no physiological or POMS data to demonstrate that ice vest cooling improved exercise in hyperthermic conditions. As it was shown in the present study T_rec only significantly differed after 45 min of seated rest in the heat following cooling, therefore future research should assess the optimum post cooling time for which exercise should begin.

Date of Award	2012
Original language	English
Awarding Institution	Coventry University
Supervisor	Mike Price (Supervisor) & Mathew Hill (Supervisor)