Influence of aerobic fitness and body fatness on tolerance to uncompensable heat stress

Abstract

This study examined the independent and combined importance of aerobic fitness and body fatness on physiological tolerance and exercise time during weight-bearing exercise while wearing a semipermeable protective ensemble. Twenty-four men and women were matched for aerobic fitness and body fatness in one of four groups (4 men and 2 women in each group). Aerobic fitness was expressed per kilogram of lean body mass (LBM) to eliminate the influence of body fatness on the expression of fitness. Subjects were defined as trained (T; regularly active with a peak aerobic power of 65 ml · kg LBM−1 · min−1) or untrained (UT; sedentary with a peak aerobic power of 53 ml · kg LBM−1 · min−1) with high (High; 20%) or low (Low; 11%) body fatness. Subjects exercised until exhaustion or until rectal temperature reached 39.5°C or heart rate reached 95% of maximum. Exercise times were significantly greater in TLow(116 ± 6.5 min) compared with their matched sedentary (UTLow; 70 ± 3.6 min) or fatness (THigh; 82 ± 3.9 min) counterparts, indicating an advantage for both a high aerobic fitness and low body fatness. However, similar effects were not evident between THigh and UTHigh(74 ± 4.1 min) or between the UT groups (UTLow and UTHigh). The major advantage attributed to a higher aerobic fitness was the ability to tolerate a higher core temperature at exhaustion (the difference being as great as 0.9°C), whereas both body fatness and rate of heat storage affected the exercise time as independent factors.

Expression of intracellular cytokines, HSP72, and apoptosis in monocyte subsets during exertional heat stress in trained and untrained individuals

“…No respirator, gloves, or overboots were worn, but the hood was over the head. The total thermal resistance of this protective ensemble has been reported previously (67), but it should be noted that these values will be slightly lower in the current study due to the absence of impermeable gloves, boots, and respirator.…”

“…It is well documented that a primary mechanism conferring improved heat tolerance in aerobically fit individuals is the ability to tolerate higher rectal temperatures (T re ) at exhaustion during uncompensable EHS (67,68). Moreover, our laboratory recently reported in the same cohort of subjects a decreased heat tolerance accompanied by enhanced circulating TNF-␣ and endotoxin concentrations in sedentary-untrained compared with endurance-trained subjects for a given level of thermal strain (68).…”

“…Subjects were divided into two groups of endurance-trained (TR, n ϭ 12) or sedentary-untrained (UT, n ϭ 11) individuals based on baseline measurements of peak O 2 consumption (V O2peak) expressed relative to lean body mass (LBM), percent body fat, and activity profiles as described previously (67,68). TR subjects were defined as actively participating in a cardiovascular training program more than three times per week and having a V O2peak Ͼ 65 ml ⅐ kg LBM Ϫ1 ⅐ min Ϫ1 .…”

Exercise does not feel the same when you are overweight: the impact of self-selected and imposed intensity on affect and exertion

“…One possibility is that overweight individuals might have compromised thermoregulatory ability, resulting in higher core or brain temperatures. [54][55][56][57] These are known to be associated with reduced ratings of pleasure and comfort during exercise. 58 Another possibility, supported by anecdotal reports collected during the present study, is that, as the intensity increases, overweight adults tend to experience more skeletal and muscular aches and pains than normalweight adults.…”

Insulated skin temperature as a measure of core body temperature for individuals wearing CBRN protective clothing

“…Collapse from heat stroke is usually associated with a T c of > 40 °C (Armstrong, 2003). While in reality many individuals will cope at temperatures between 39 °C to 40 °C, this is not an acceptable upper limit in a working environment, especially taking into consideration that the critical T c for individuals working in conditions of uncompensable heat stress is often reported as 38.5 °C (Montain et al, 1994, Selkirk andMcLellan, 2001). Using this criterion (38.5 °C), and the SEE of 0.20 °C, individuals would have to be removed from work at a predicted T re of 38.1 °C.…”