Effect of base layer materials on physiological and perceptual responses to exercise in personal protective equipment.

Ten men (non-firefighters) completed a 110 min walking/recovery protocol (three 20-min exercise bouts, with recovery periods of 10, 20, and 20 min following successive bouts) in a thermoneutral laboratory while wearing firefighting personal protective equipment over one of four base layers: cotton, modacrylic, wool, and phase change material. There were no significant differences in changes in heart rate, core temperature, rating of perceived exertion, thermal discomfort, and thermal strain among base layers. Sticking to skin, coolness/hotness, and clothing humidity sensation were more favorable (p < 0.05) for wool compared with cotton; no significant differences were identified for the other 7 clothing sensations assessed. Separate materials performance testing of the individual base layers and firefighting ensembles (base layer + turnout gear) indicated differences in thermal protective performance and total heat loss among the base layers and among ensembles; however, differences in heat dissipation did not correspond with physiological responses during exercise or recovery.

The effect of precooling on cardiovascular and metabolic strain during incremental exercise.

The purpose of this study was to investigate the effect of precooling on the chronotropic index defined as the slope of the heart rate (HR) and oxygen uptake during incremental exercise. Ten men performed incremental exercise following 2 conditions: control (rest in a thermoneutral laboratory, 21.5 ± 0.7 °C; performed first) and precooling (cold-water immersion, 23.1 ± 0.2 °C). Prior to exercise, core temperature was significantly lower for precooling (36.6 ± 0.3 °C) compared with control (37.1 ± 0.4 °C; p < 0.001) and remained lower throughout exercise (p < 0.05). Time to volitional fatigue during the incremental exercise test was significantly longer in the control (914 ± 97 s) compared with precooling (889 ± 97 s; p = 0.015). Precooling reduced HR by 8-10 beats·min(-1) compared with control throughout exercise (peak HR: precooling, 178 ± 9 beats·min(-1); control, 188 ± 6 beats·min(-1); p = 0.001). Oxygen uptake did not differ between conditions (p > 0.05). The chronotropic index did not differ between conditions (p = 0.301); however, the y intercept was significantly lower (p = 0.009) for precooling (53.6 ± 11.0) compared with control (67.3 ± 11.0). Thus, the benefit of precooling was a lower HR that was maintained throughout exercise rather than a reduced rate of rise in HR. These results suggest the potential use of precooling to mitigate cardiovascular strain in individuals working at elevated metabolic rates. However, the reduced exercise time warrants consideration.