Efficacy of air and liquid cooling during light and heavy exercise while wearing NBC clothing

Background: Studies, to date, have not revealed the extent to which the hea t strain of continuous heavy exercise while wearing NBC protective clothing can be reduced by providing liquid- or air-cooling and whether one system is more effective than the other in aiding heat transfer from the body and the clothing. It was of interest to know to what extent present-day cooling technologies can reduce the heat strain of light and heavy exercise in NBC clothing and to compare these reductions to other strategies that have emp loyed changes in clothing design. Hypothesis: It was hypothesized that ther e would be no difference between the liquid and air cooling systems and tha t sufficient cooling power would be delivered to the body to reduce the hea t strain of heavy exercise to a level similar to that experienced with ligh t exercise when no cooling was provided. Methods: Eight males performed 6 r andomized exposures for a maximum of 3 h at 40 degrees C and 30% relative h umidity that involved either light (L) (walking at 3.5 km.h(-1) or heavy (H ) (walking at 4.8 km.h(-1) and a 5% grade) exercise while wearing the NBC p rotective clothing ensemble with no cooling (N), liquid (L) or air (A) cool ing. Results: For L exercise, tolerance time was significantly increased fr om 100 min with N to the maximum of 3 h with either cooling system. There w as no difference between L and A cooling in the extent of the changes in re ctal temperature, heart rate and heat flow. For H exercise, tolerance time was significantly increased 150% from 57 min with N to 149 min with L and 1 40 min with A. These latter values for HL and HA were not different from ea ch other but both were significantly greater than L exercise with N. Rectal temperature increased more quickly during HL compared with HA during the f irst 60 min of exposure but there were no differences between cooling trial s for the remainder of the heat exposure. Conclusions: It was concluded tha t sufficient cooling power could be delivered to the body to effectively re duce the heat strain of wearing NBC protective clothing during heavy exerci se in a hot environment to a level comparable to or slightly lower than tha t experienced with light exercise and no cooling.