Search

Differences in oxygen consumption between individuals and also within individuals on 4 different tasks and at 2 rates of energy expenditure were examined. Criteria are proposed for indicating differences in physiological ‘ skill ’ between individuals and in some tasks such differences were found. Weight was found to be correlated with maximum oxygen intake, the factor which sets a limit to the maximum level of endurance work, and is also correlated with oxygen consumption in two of the tasks. It is considered that differences between individuals in maximum oxygen intake is more important than are differences in oxygen consumption in tasks requiring prolonged physical effort. Gross mechanical efficiencies were estimated in order to compare the mean efficiencies of this group of men when performing different tasks.

23 Bantu male subjects were studied at various levels of work on a bicycle ergometer in order to establish the level of oxygen consumption, as a percentage of their maxima, at which laotate and “excess lactate” started to increase in the blood.

The concentration of lactate and pyruvate was determined in the blood of 13 subjects at three aerobic and four anaerobic levels of work before and after a period of training on a constant work-rate bicycle ergometer. In addition each man's maximum oxygen intake was established on either the bicycle ergometer or the motor-driven treadmill, by means of the Douglas bag technique, before and after the period of training. The results obtained demonstrated that a regime of training influenced the maximum oxygen intake and also the level of oxygen intake at which “excess lactate” starts to appear in the blood. During the training of the subjects these two physiological parameters changed independently of each other but large individual differences were also observed. The mean maximum oxygen intake of the men, which was 2.888l/min before training, increased to 3.060l/min (a change of 7 per cent) after the men had trained for a period of 4 to 16 weeks. During this period of training the mean level of oxygen intake, expressed as a percentage of the maximum value, at which “excess lactate” appeared increased from 46 to 62 per cent. The relationship between the degree of fitness and the appearance of anaerobic metabolism during work is discussed. In untrained individuals the onset of anaerobic metabolism occurred at 40–45 per cent of the maximum oxygen intake, in trained individuals at 55–60 per cent and in the exceptionally well-trained men at about 70 per cent.

Bushmen in the Kalahari desert fulfill two criteria for acclimatization to heat. They exercise actively, in hunting, in relatively severe heat in midsummer. Compared with unacclimatized Bantu they have higher sweat rates per square meter and lower heart rates. However, rectal temperatures are not much lower than those of unacclimatized Bantu. River Bushmen present a paradoxical picture. In summer sweat rates are higher than in winter, but are not as high as desert Bushmen. Summer heart rates are, however, higher than in winter. Rectal temperatures in the two seasons are similar. The higher sweat rates in summer are good evidence of better acclimatization than in winter; the higher heart rates may be a reflection of differences in physical fitness in the two seasons. association of morphology and metabolism on cold exposure; cold responses of Bantu, Bushmen, and Caucasians; heat conductance and skinfold thickness in cold; metabolisms of Bantu, Bushmen, and Caucasians in cold; toe, finger, and rectal temperatures of different ethnic groups in cold Submitted on February 4, 1964

Heat reactions of 20 Caucasian and 22 Bantu males were compared, first in the unacclimatized state and then in the acclimatized state. The study was conducted at temperatures of 90 F wet-bulb and 93 F dry-bulb at a work rate of 1 liter O2/min consumption. The performances of the unacclimatized Bantu were superior to those of the Caucasians. All 22 Bantu completed the 4-hr experiment, while 10 Caucasians failed. The mean rectal temperature of the Bantu was significantly lower than that of the Caucasians, but not the mean heart rate and mean sweat rate. When both groups were highly acclimatized all men from both groups completed the 4-hr experiment, and their reactions to heat were significantly different from their reactions in the unacclimatized state. Sweat rates, particularly, increased very much. The differences between the two highly acclimatized groups in rectal temperatures, heart rates, and sweat rates (except the 4th hr) were not significant. Although superior in the unacclimatized state, the Bantu does not appear to have an inherent advantage in the ability to regulate the body temperature. Caucasians versus Bantu in reactions to heat; physiological reactions in exposure to heat Submitted on August 19, 1963

THE level of oxygen consumption, compared with the maximum intake, at which an individual can work safely for 6–8 h, from month to month, has been variously defined. The Max Planck Arbeitsphysiologie Institute group in Dortmund support the idea that the rate of oxygen intake equivalent to the “Pulsdauerleistungsgrenze” (a heart-rate of about 120 beats/min) is the safe limit. The sole basis of this criterion is that, in their experience, the heart-rate continues to rise and does not remain in a steady state when the level of oxygen consumption has caused the heart-rate to exceed 120 beats/min. The “Pulsdauerleistungsgrenze” is said to occur at about 30 per cent of the individual's maximum level of oxygen intake1. Christensen et al.2 have a sounder, even if empirical, basis for their safe limit. They found that men engaged on hard manual work, such as lumber-jacking, on high financial incentives, do not, in general, work at a level which exceeds 50 per cent of the maximum level of oxygen intake.

Eleven men per sample of Caucasian and Bantu males were exposed for 2 hr in a climatic chamber at various air temperatures ranging from 5 to 27 C, and a wind velocity of 80–100 ft/min. When expressed per square meter surface area the metabolism of the Bantu was greater in the range above 18 C and below 6 C. Average skin temperatures were similar for both groups, but between 27 and 17 C the toe and finger temperatures of the Caucasians were significantly higher than that of the Bantu—the difference at 27 C being 5 C for the fingers and 3.6 C for the toes. Rectal temperatures of both groups were similar between 27 and 17 C. With the rectal temperatures at 27 C air temperature as the criterion, it was found that as the air temperatures decreased below the 27–17 C range the rectal temperatures of the Bantu fell linearly, while the rectal temperatures of the Caucasians rose steadily. There is no doubt that in certain ranges of air temperatures there are significant differences between the cold reactions of Caucasians and the Bantu. cold adaptation; ethnic differences in response to cold; metabolic and body temperature reactions to cold; metabolic response to body temperature; metabolic reactions of ethnic groups Submitted on July 15, 1963

The physiological reactions to cold of nine female Caucasians were examined and compared with the reactions of a sample of male Caucasians. The experiment was conducted in the climatic chamber of the Applied Physiology Laboratory at air temperatures of 27 and 5 C, with a wind velocity of 80–100 ft/min. The sample of nine did not provide for intermediate temperature studies. The metabolic rates of the females were lower than those of the males, at both 27 and 5 C, but when expressed per square meter no differences were found. Finger and toe and rectal temperatures were the same for both sexes at 5 C, but the average female finger temperature was lower than that of the males at 27 C. The average female skin temperature was 2 C lower than that of the males. This indicates a greater subcutaneous insulation for females and this is confirmed by skinifold measurements. Both Caucasian sexes therefore display an increase in rectal temperature with fall in air temperature, which contrasts markedly with the Bantu and Bushman, both of whom show a decrease in rectal temperatures. Caucasian females and cold; cold responses of Caucasian females Submitted on September 17, 1963