Effect of inspiratory resistance to prolonged exercise in a hot environment wearing protective clothing

The effects of inspiratory resistance on prolonged work in a hot environment wearing a nuclear, bacteriological and chemical warfare (NBCW) mask and overgarment were assessed in 10 males. Subjects walked on a treadmill at 5 km/hr, 2% gradient, until their core temperature reached 39 degrees C or for a duration of 90 min. Rectal temperature, heart rate, ventilation, oxygen consumption and rate of perceived breathing were measured. There were no differences between break-point time without the canister (62.2 +/- 21 min) and with the canister (58.9 +/- 17 min). Regression analysis indicated that the mean core temperature increased by 0.02 degrees C for every minute of work performed and heart rate by 6 beats/min for every increase of 0.2 degrees C in core temperature. Reduction in heat transfer brought about by wearing the protective overgarment and mask with or without the canister will significantly increase core temperature and limit the performance of moderate work to approximately 1 h in a moderately fit individual.