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tral environment that results in a significant elevation in maximal oxygen uptake reduces the core temperature threshold for the onset of sweating (Roberts et al., 1977) but does not necessarily increase total body sweat rate (Taylor, 1986). Sweat rates of male subjects have been found to be positively correlated with aerobic capacity (Greenleaf et al., 1972).

Heat Acclimatization

Maximal sweating capacity can rise from 1.5 liters per hour in a healthy unacclimatized man to as much as 2 to 3 liters per hour in a highly trained acclimatized soldier (Wenger, 1988). One of the highest sweat rates ever observed was recorded on Alberto Salazar during the 1984 Olympic Marathon. Salazar was running at 85 percent of (5.2 meters per second) and had a body weight loss of 5.43 kg (-8.1 percent body weight) despite an estimated fluid ingestion of 1.88 liters. This weight loss was equivalent to a sweat rate of 3.71 liters per hour (Armstrong et al., 1986).

Age and Gender

Military personnel range in age from 18 to 50 years and comprise 14 percent women. The effects of age and gender on thermoregulation, particularly the sweating response to exercise and thermal stress, have been elegantly reviewed by Drinkwater (1986). Contrary to popular opinion, differences in physiological responses to thermal stress cannot be attributed to differences in gender or age. When differences do appear among subjects of

TABLE 5-2 Mean Sweat Rates of Four Highly Trained Endurance Athletes Who Walked (3.5 mph) for 5 to 7 Hours in Hot-Wet, HotDry, and Neutral Climates

 

Sweat Rate (liters per hour)

Subject

Hot-Wet Environment*

Hot-Dry Environment

Neutral Environment

KM

778

1247

178

JC

659

1198

302

MN

838

1234

272

BC

590

1159

265

Mean ± SE

715 ± 56

1210 ± 20

254 ± 27

* 37/33°C dry bulb/wet bulb.

50/28°C dry bulb/wet bulb.

27/13°C dry bulb/wet bulb.



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