This study was conducted to evaluate the effectiveness of a commercial, personal ice cooling vest on tolerance for exercise in hot (35°C), wet (65% relative humidity) conditions with a nuclear biological chemical suit (NBC). On three separate occasions, 10 male volunteers walked on a treadmill at 3 miles per hour and 2% incline while (a) seminude (denoted CON), (b) dressed with a nuclear, biological, chemical (NBC) suit with an ice vest (V) worn under the suit (denoted NBCwV); or (c) dressed with an NBC suit but without an ice vest (V) (denoted NBCwoV). Participants exercised for 120 min or until volitional fatigue, or esophageal temperature reached 39.5°C. Esophageal temperature (T(es)), heart rate (HR), thermal sensation, and ratings of perceived exertion were measured. Exercise time was significantly greater in CON compared with both NBCwoV and NBCwV (p < 0.05), whereas T(es), thermal sensation, heart rate, and rate of perceived exertion were lower (p < 0.05). Wearing the ice vest increased exercise time (NBCwoV, 103.6 ± 7.0 min; NBCwV, 115.9 ± 4.1 min) and reduced the level of thermal strain, as evidenced by a lower T(es) at end-exercise (NBCwoV, 39.03 ± 0.13°C; NBCwV, 38.74 ± 0.13°C) and reduced thermal sensation (NBCwoV, 6.4 ± 0.4; NBCwV, 4.8 ± 0.6). This was paralleled by a decrease in rate of perceived exertion (NBCwoV, 14.7 ± 1.6; NBCwV, 12.4 ± 1.6) (p < 0.05) and heat rate (NBCwoV, 169 ± 6; NBCwV, 159 ± 7) (p < 0.05). We show that a commercially available cooling vest can significantly reduce the level of thermal strain during work performed in hot environments.

This is the first study to quantify how much 14 d of heat acclimation can increase whole-body evaporative heat loss, which can improve by as much as approximately 11%.

Hardcastle S, Kenny GP. Whole body heat loss is reduced in older males during short bouts of intermittent exercise. Am J Physiol Regul Integr Comp Physiol 305: R619 -R629, 2013. First published July 24, 2013 doi:10.1152/ajpregu.00157.2013.-Studies in young adults show that a greater proportion of heat is gained shortly following the start of exercise and that temporal changes in whole body heat loss during intermittent exercise have a pronounced effect on body heat storage. The consequences of short-duration intermittent exercise on heat storage with aging are unclear. We compared evaporative heat loss (HE) and changes in body heat content (⌬Hb) between young (20 -30 yr), middle-aged (40 -45 yr), and older males (60 -70 yr) of similar body mass and surface area, during successive exercise (4 ϫ 15 min) and recovery periods (4 ϫ 15 min) at a fixed rate of heat production (400 W) and under fixed environmental conditions (35°C/20% relative humidity). HE was lower in older males vs. young males during each exercise (Ex1: 283 Ϯ 10 vs. 332 Ϯ 11 kJ, Ex2: 334 Ϯ 10 vs. 379 Ϯ 5 kJ, Ex3: 347 Ϯ 11 vs. 392 Ϯ 5 kJ, and Ex4: 347 Ϯ 10 vs. 387 Ϯ 5 kJ, all P Ͻ 0.02), whereas HE in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 Ϯ 13, Ex2: 355 Ϯ 13, Ex3: 371 Ϯ 13, and Ex4: 365 Ϯ 8 kJ). HE was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater ⌬Hb in older (267 Ϯ 33 kJ; P ϭ 0.016) and middle-aged adults (245 Ϯ 16 kJ; P ϭ 0.073) relative to younger counterparts (164 Ϯ 20 kJ). As a result of a reduced capacity to dissipate heat during exercise, which was not compensated by a sufficiently greater rate of heat loss during recovery, both older and middle-aged males had a progressively greater rate of heat storage compared with young males over 2 h of intermittent exercise. evaporative heat loss; aging; calorimetry; thermal transients A NUMBER OF STUDIES HAVE EXAMINED age-related differences in thermoregulatory control during prolonged exercise (range 30 -90 min) in the heat [range: 30 -49°C/20 -60% relative humidity (RH)] (4, 11-13, 20, 23, 26, 29, 33, 34). Some studies reported no differences in thermoregulatory function (4,20,23,29,33), whereas others found significant age-related impairments in heat loss capacity (e.g., reduced local sweating rate/onset/sensitivity and/or greater increments in core and skin temperatures) (11-13, 26, 34). It is possible that these discrepancies reflect that in some studies, older adults were able to achieve heat balance, while in other studies, heat load exceeded their physiological maximal sweating capacity; hence, differences in local sweat rate and/or core temperature were evident. What these studies did not examine, however, is whether age-related impairments in heat loss capacity occur during exercise of short duration (i.e., 15 min) when the rate of heat storage has been shown to be the greatest (21).At the onset of exercise, the rate of metabolic heat production increases immediately and is not i...

We examined differences in dynamic heat balance between males and females during intermittent exercise. Six males (M) and six females (F) performed three 30-min bouts of exercise (Ex1, Ex2, Ex3) at a constant rate of metabolic heat production (M - W) of approximately 500 W separated by three 15-min periods of inactive recovery. Rate of total heat loss (M - W) was measured by direct calorimetry, while M - W was determined by indirect calorimetry. Esophageal (T (es)) was measured continuously. Exercise at a constant M - W of approximately 500 W, was paralleled by a similar HL between sexes at the end of Ex1 (M: 462 +/- 30 W, F: 442 +/- 9 W, p = 0.117), Ex2 (M: 468 +/- 28 W, F: 508 +/- 18 W, p = 0.343), and Ex3 (M: 469 +/- 17 W, F: 465 +/- 13 W, p = 0.657). Consequently, changes in body heat content were comparable after Ex1 (M: 218 +/- 21 kJ, F: 287 +/- 35 kJ, p = 0.134), Ex2 (M: 109 +/- 18 kJ, F: 158 +/- 29 kJ, p = 0.179), and Ex3 (M: 92 +/- 19 kJ, F: 156 +/- 35 kJ, p = 0.136). However, females had greater overall increases in T (es) at the end of Ex3 (M: 0.55 +/- 0.25 degrees C, F: 0.97 +/- 0.26 degrees C, p

The current study demonstrated that heat balance was not achieved and ΔTb and ΔHb were inconsistent, suggesting that the TLV may not adequately protect workers during work in hot conditions.