Sixty-nine whites (38 men and 31 women) aged 17 to 88 years and 48 blacks (19 men and 29 women) aged 17 to 61 years were studied. Each person walked in desert heat for 1 hour at a rate requiring 40% of aerobic capacity. Observations were recorded on their rectal temperature (Tre), skin temperature (Tsk), heart rate (HR), blood pressure, and sweat rate (SR). Older men and women of both races were able to complete their walks without any ill effects. Age, per se, did not significantly reduce elderly individuals' ability to tolerate the combined stress of dry heat and exercise. Men of both races had higher sweat rate and lower heart rate and rectal and skin temperature than women working at the same percentage of aerobic capacity. Success of thermoregulation at 40% of aerobic capacity of blacks and whites was equal, but in both races men thermoregulated more successful than women. Our data suggest that thermoregulatory capacity of humans under desert conditions differs between sexes and is not influenced significantly by age or race except for differences in aerobic capacity.

Many investigators have sought, but failed to find, ethnic differences in the number and regional distribution of active sweat glands. In this study measurements have been made of sweat secreted on one hand and also on the whole body of Whites and Blacks walking in desert heat. Whites numbered 31 men and 27 women, ages 30 to 88 years; there were 21 Black men and 31 Black women, ages 16 to 61 years. Each walked on three occasions for 1 hour at a rate that required an oxygen consumption of about 40% of aerobic capacity. Ambient temperature ranged from 32 to 44 degrees C in 1979 and 1980; means were 38.4 degrees C in 1979 and 36.7 degrees C in 1980. There was no sweat in the gloves of many Blacks; this was true of only a few Whites. Volume of body sweat increased in both races with rate of walking; volume of hand sweat increased more in Whites than in Blacks. The Mann-Whitney test revealed that volumes of hand sweat were significantly greater for Whites than for Blacks. It was concluded that in desert walks most Whites and few Blacks sweat freely on their hands. In samples of hand sweat, Na+, K+, and Cl- were determined. Concentrations of each ion varied widely in both races, and were unrelated to race. Concentrations of Na+ and Cl- generally are somewhat higher in hand sweat than in body sweat; concentrations of K+ are much higher. It follows that the values for concentration of Na+ and Cl- reported in Table 3 probably are somewhat higher than would have been found in body sweat, and concentrations of K+ are probably much higher.

Aerobic capacity (VO2 max) and body fat were measured indoors and VO2 was measured at about 36 to 42 degrees C in desert walks or runs in 69 adults aged 17 to 88 years. Eleven were athletic youths, and many of the older adults had participated in jogging programs. Body fat increased and VO2 max decreased with age, although there were notable exceptions. Rates of walking and running were planned to require about 40% of VO2 max. Midway in each walk VO2 (ml O2/horizontal m . kg) served as a measure of skill; skill was high in 10 of 11 youths who did many walks or runs. Each older adult did three walks; skill improved. In four groups with some persons aged 50 and older with body fat up to 40%, skill in their third walk matched that of youths. The least fit women and the least fit men did not attain that level of skill.

The burro ( Equus asinus ) can withstand deprivation of both food and water for up to 48 hours even in summer heat. This ability depends in part on his capacious cecum and colon where food is stored and is digested by bacterial action for hours after his last meal. In eight such periods of deprivation maximum temperatures ranged from 35 to 45°C and estimated increases in osmotic pressure in two burros ranged up to 17%. Given free choice of hay and water at the end of deprivation they chose hay always when estimated increase in osmotic pressure was less than 10%. In one case the second 24-hour period included an eight-hour walk. In this case the estimated increase in osmotic pressure was 17% in both and both chose water first. Their ability to eat dry hay after long periods of dehydration is essential to their survival in hot deserts where they can graze for 24 hours before returning to a water source.

1.1. Sweat of two burros (Equus asinus) was collected after two desert walks, one at 38°C, one at 41°C.2.2. Sweat from one burro was about twice as concentrated as from the other. In that respect and in respect to concentrations of chloride, sodium and potassium their sweat was like that of man.3.3. Low concentrations of bicarbonate were present in burros' sweat contrasted with little if any in man's.4.4. Urea nitrogen plus ammonia nitrogen were found in higher concentrations in burros' sweat than in man's sweat.

Cardiac output and stroke volume were measured in two environments and at metabolic rates ranging from rest to the maximum rate that could be sustained for 25 minutes. One environment was indoors at about 23 degrees C, the other outdoors in desert sunshine and low water vapor pressure. The age range of the one female and four of the male subjects was from 19 to 40; the fifth male subject was 85 years old. Cardiac output was the same in the two environments; stroke volume was less at higher metabolic rates in the heat. The cardiac output for the old man was about one-tenth less and stroke volume about 20 ml less than that observed for the same work 50 years earlier.

Kangaroo rats deprived of food ran themselves to death in 48 h in wheel cages. Despite the loss of 14.5% of body weight the ratio of water to protein was the same after the run as it was in control rats. Metabolic measurements at rest and in the running wheel and weight loss in the 48-h run were used to estimate fuels used and water expended. Two-thirds of the initial amount of fat and 9% of the protein were metabolized. The terminal mean percentage of body fat was about twice that observed in rats trapped in the spring of 1967, when seed production was low: death in the 48-h run could not have been due to depletion of body fat alone. The powerful activity drive seen in hungary kangaroo rats presumably is intensified in dry years when food is scarce and may deplete their reserves enough to result in death from starvation.

Annals of the New York Academy of SciencesVolume 301, Issue 1 p. 550-560 A PHYSIOLOGICAL PROFILE OF A JOGGING CLASS: YOUNG AND OLD, MALE AND FEMALE* A. Goldman, A. Goldman Mathematics Department University of California Davis, California 95616 Mathematics Department, University of Nevada Las Vegas, Las Vegas, NV 89154.Search for more papers by this authorD. B. Dill, D. B. Dill Laboratory of Applied Physiology Desert Research Institute Boulder City, Nevada 89005Search for more papers by this author A. Goldman, A. Goldman Mathematics Department University of California Davis, California 95616 Mathematics Department, University of Nevada Las Vegas, Las Vegas, NV 89154.Search for more papers by this authorD. B. Dill, D. B. Dill Laboratory of Applied Physiology Desert Research Institute Boulder City, Nevada 89005Search for more papers by this author First published: October 1977 https://doi.org/10.1111/j.1749-6632.1977.tb38229.xCitations: 2 * This work was supported in part by National Institutes of Health Grant AG 00437-04A1 and by a University of Las Vegas research grant. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume301, Issue1The Marathon: Physiological, Medical, Epidemiological, and Psychological StudiesOctober 1977Pages 550-560 RelatedInformation

1. 1. For four species of rodent, man, and burro, we measured the rates of evaporation required to maintain homeothermy during exposure to desert heat. 2. 2. Required rates of evaporation for laboratory mice, laboratory rats and men were exponentially related to body weight. Kangaroo rats required a significantly lower amount of evaporation than the laboratory mice and rats. 3. 3. During walks in the open desert, man and burro required a two to three-fold increase in evaporation. 4. 4. When the metabolic cost of walking is expressed as a proportion of resting metabolism where unity equals one met, the evaporative requirement is directly related to the met with a slope of 0.33% body weight evaporated/hr/met. 5. 5. For man, the extreme hourly evaporation rate is 2.9% of the body weight. From this we calculated a limiting value for steady state exercise in desert heat that is about one-half the value sustained by a marathon runner in cool weather.

Tolerance for sustained activity in the desert at about 40 degrees C was assessed on high school students, mostly athletically oriented and scholastically superior. The 14 males compared with the 12 females had an aerobic capacity greater by about one-half and a percentage of body fat smaller by about one-half. Each sex attained about the same percentage of aerobic capacity in their maximal sustained effort. This involved an increase in metabolic rate of 3 to 5 fold in females and 6 to 8 fold in males. In maximal sustained effort responses of males and females were alike in respect to rectal and skin temperatures and heart rate. At a rate at which nearly all walked for one hour, 100 m/min, there were no significant differences in metabolic rate, sweat rate nor in composition of sweat. Running at 120 m/min required maximal effort by most females; their maximal sweat rates ranged from 7.4 to 14.2 ml/m2.min. Most males were able to run at 160 m/min for one-half hor to one hour; their maximal sweat rates ranged from 11.3 to 14.6 m/m2.min. Superior capacity of males over females for sustained exercise in desert heat is related to their higher aerobic capacity and not to a difference in capacity for thermoregulation.

Laboratory of Environmental Patho-Physiology, Desert Research Institute, Boulder City, Nevada, and the USAF School of Aerospace Medicine, Brooks AFB, TX Indiana University School of Medicine Myers Hall Bloomlngton. IN 47401

lb Oddershede, Laboratory of Environmental Patho-Physiology, Desert Research Institute, University of Nevada, Boulder City, Nevada Supported by NIH Grant (RO1 HD0565-04A1). Desert Research Inst. 500 Date St. Boulder City, NV 89005

Seven young men undertook a desert walk of 30 km at a rate of 100 m/min. Six finished; the seventh stopped after 24 km. Each satisfied his thirst with cool tap water each hour. Periodic observations included metabolic rate, blood pressure, heart rate, rectal and skin temperature, body weight, and volume of water drunk. Hand sweat was collected each hour and body sweat residues on the skin were collected at the end of the walk. Subjective reports revealed portents of breakdown: aching muscles, painful joints, hot or blistered feet, hunger, and boredom. Cardiovascular adjustment and temperature regulation maintained tolerable conditions. The volumes of water evaporated by the 5-h walkers were about the same. Wet bulb temperatures were below 25 degrees C; all sweat evaporated and was available for temperature regulation. The volume of water drawn from body reserves was closely correlated with concentration of chloride in body sweat; the volume of water that satisfied thirst maintained osmotic pressure.