Tolerance for Intermittent Exercise in Military Clothing Is Improved by Wearing a Ventilated Vest in Hot, Dry Conditions

Contact person: [email protected] INTRODUCTION There has been much recent research interest in microclimate cooling for individuals working in hot climates whilst wearing protective clothing (Bomalaski et al. 1995; Chen et al. 1997; Cheuvront et al. 2003; Chinevere et al. 2008). Attempts have been made to develop cooling garments that augment convective (air cooled garments), conductive (liquid cooled garments) and evaporative cooling. The purpose of such garments is to delay any heat-related deterioration in physical and cognitive performance and prevent the onset of heat illness. Military personnel (e.g. infantry) and some occupational groups (e.g. emergency services) are particularly vulnerable to heat illness due to the requirement to work whilst wearing protective clothing that impedes heat loss. This requirement creates the need for cooling garments that should form an integrated part of the overall protective clothing assembly. Relatively few laboratory-based studies have tested the efficacy of microclimate ventilation in air temperatures above 43°C because of the risk of heat gain through forced convection and an increased risk of burning. Additionally, the test protocols used have often been short (e.g. 80 minutes, Hadid et al. 2009; 120 minutes, Verniuew et al. 2008) despite the intended use of garments for longer durations. For example, soldiers deployed with an armoured vehicle require a minimum of 6 h of effective use without battery replenishment. Shorter duration studies can demonstrate the short-term efficacy of microclimate ventilation but do little to inform about the longer term operational significance of using such a garment. A further methodological consideration is that shorter studies can be misleading by being insufficient to allow the clothing assembly to equilibrate in terms of garment temperature and moisture content. Garments like body armour can act as a large heat sink in the early stages of a test if not pre-acclimated to the test environment, and the thermal profile of individuals will alter as the clothing system equilibrates. For reasons related to battery life, the availability of a suitable heat sink, logistic and operating restrictions (i.e. noise), the tendency has been towards the use of convective/evaporative rather than conductive cooling. The aim of this study was to determine the efficacy of a ventilated vest during long duration exposure to hot, dry conditions. This study tested the hypothesis that the ventilated vest garment would extend exercise time and remain effective during rest and exercise for up to 6 h in hot (45°C), dry (10% RH) ambient conditions.