Intermittent microclimate cooling during rest increases work capacity and reduces heat stress

Abstract

Requirements for special protective equipment while working in hazardous environments can present a significantly increased thermal burden and early onset of physical fatigue. Ambulatory (backpack) or tethered personal cooling can accelerate metabolic heat removal, but is often not practical from an ergonomic standpoint. The efficacy of incorporating personal cooling during non-ambulatory rest periods was evaluated in subjects (n = 8) with varying levels of fitness. Treadmill work (approximately 475 W, 40% VO2 max) was alternately performed for 30 min followed by 30 min of rest. Subjects walked and rested under three separate experimental conditions: (1) control (C), in which light clothing was worn; (2) CPE, in which a chemical protective ensemble (CPE) was worn, and (3) CPE plus intermittent microclimate cooling (COOL). The WBGT condition for all trials was 31 degrees C. During the COOL trial the subjects additionally wore a personal cooling vest which allowed for the circulation of chilled liquid over the torso during rest. Under C conditions, relatively modest changes in rectal temperature (Tre) were observed, which stabilized over time. CPE wear resulted in a progressive rise in Tre and early fatigue. The addition of intermittent cooling during each rest cycle (COOL trial) significantly attenuated heat storage such that an oscillating, but equilibrated Tre was established and work capacity was at least doubled. Moreover, the perceived cooling effect was appreciable for all subjects. Therefore, intermittent personal cooling provided a useful means of enhancing work productivity and may have application for certain military and industrial personnel performing heavy work in hot environments. This approach should provide a practical alternative for reducing stress/fatigue when work/rest cycles are employed.