Optimization of cooling regimes in a Liquid Cooling Garment (LCG) to support thermal balance and comfort of the human body during exercise.

Abstract

The primary purpose of the study was to assess the effectiveness of different cooling regimes within a liquid cooling garment (LCG) to provide physiological thermal balance and subjective thermal comfort during different intensities of physical exertion. The second purpose was to examine the dynamics of finger temperature (Tfing) and finger heat flux (HFfing) responses to changes in thermal indices reflecting the thermal status of the body core and/or shell. Eight males ages 28.9±8.3 completed an exercise protocol consisting of 4 stages of treadmill walking/running (300-600 Watts) and one rest stage. Four different cooling regimes were tested in separate sessions: subjective cooling control by participant selecting the skin surface cooled (CON1); choice of different inlet water temperatures (Tin), whole body cooling (CON2); fixed Tin; at 7°C, whole body cooling (CON3); adjusted Tin based on different metabolic rates of exercise, whole body cooling (CON4). CON1/2 were acceptable means of LCG cooling control, but showed disadvantages because of delays in self-initiated cooling and frequent failure to select an appropriate cooling intensity. CON3 exhibited the highest amount of heat flow, but was not significantly more effective than CON4 in lowering core temperature (Tcore), heart rate, and perceived exertion. In addition, CON3 caused thermal discomfort and a high level of cold on the skin surface. CON4 appeared an effective cooling regime to support thermal balance and subjective comfort. Sweat rate was positively related to increase in Tcore; however, effects of regional skin wetness on development of thermal discomfort were inconclusive. The dynamics of Tfing/HFfing were highly associated with body heat content and mean body temperature and indicated its potential use as thermal indices to monitor thermal balance of the body. In addition, attention needs to be paid to non-thermoregulatory factors that also influence the dynamics of these indices. The findings suggest that future studies need to focus on harnessing human thermodynamic characteristics to advance the cooling capacity and design of a LCG. The combination of both conductive and convective cooling regimes seems optimal to better support human thermal balance and comfort under physical exertion.