Intermittent microclimate cooling during exercise-heat stress in US army chemical protective clothing

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2min on-off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30 degrees C, 30% relative humidity wearing the LCG under the MOPP3 during 80min of treadmill walking at 224 +/- 5 W (.) m(-2). Water temperature to the LCG was held constant at 21 degrees C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 +/- 0.2 degrees C) in NC, which was greater than IC (0.5 +/- 0.2 degrees C) and CC ( 0.5 +/- 0.3 degrees C) (p < 0.05). Mean skin temperature was higher during NC (36.1 +/- 0.4 degrees C) than IC ( 33.7 +/- 0.6 degrees C) and CC (32.6 +/- 0.6 degrees C) and mean skin temperature was higher during IC than CC (p < 0.05). Mean heart rate during NC (139 +/- 9 b (.) min(-1)) was greater than IC ( 110 +/- 10 b (.) min(-1)) and CC ( 107 +/- 9 b (.) min(-1)) (p < 0.05). Cooling by conduction (K) during NC (94 +/- 4 W (.) m(-2)) was lower than IC ( 142 +/- 7 W (.) m(-2)) and CC ( 146 +/- 4 W (.) m(-2)) (p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing.