Heart Size, Negro vs. White, Superior ability of Negroes

Heart Size

Heart size is related to constitutional type and thoracic circumference. Measurements of heart size in 233 athletes by orthodiagrams indicate moderate hypertrophy as compared with Hodges-Eyster standards. Such hypertrophy is judged to be normal for athletes. 30 If the larger than average heart is associated with a high vital capacity, the athlete usually also has a slower than average pulse rate and low blood pressure and possesses a large capacity for performance of work.

Negro vs. White

Negroes show a higher rate of sickness absenteeism in industry, but as the occupations and socio-economic status of the Negro and white males become more nearly alike the excess of the frequency rate of disabilities among Negroes tends to decrease, if not to disappear entirely. Negroes can stand humid heat better than white workers. The rate of sickness absenteeism in very humid climates is lower in Negroes than in whites.

The superior ability of Negroes to work in the heat is due in part to greater efficiency, a higher ratio of body surface to weight, the secretion of a more dilute sweat and a greater water intake. Negro and white sharecroppers and a group of northern whites were tested during a summer in Mississippi. Subjects walked for 2 hours on a motor driven treadmill at a rate which elevated the metabolism to 7 times basal. Room temperature averaged 88° F. and humidity 79 per cent. This work raised the body temperature of the partially acclimatized northern white men to intolerable levels, increased their heart rates to nearly maximal values and forced most of the men to discontinue the walk before the end of the two hours. Negro sharecroppers who were acclimatized by field work performed the walk without marked elevation of body temperature or heart rate. They perspired less but drank more water than did the northern whites. White sharecroppers, also accustomed to field work, were intermediate between the other groups in adaptability to the conditions of the experiment. The superiority of the Negro sharecroppers was related to lower energy requirements in performing the walk. Negro servants were no more successful than northern whites in regulating body temperature, but were able to sweat at much higher rates. Most of the Negroes reached an equilibrium with a rectal temperature of about 101° F. and a pulse rate of 150 as compared with about 102° F. and 170 in the white workers. Sweating was of the order of one to two liters an hour. The major item was superior cardiovascular condition. Final mechanical efficiencies were 25.6 per cent in Negroes and 27.5 per cent in whites. Of 23 Negroes, two were below the white average, and of 7 whites, one was better than the average Negro.

In maximal work Negroes reach a greater blood lactate concentration, have a slightly lower maximum oxygen consumption and breathe more rapidly, thus using a smaller fraction of the vital capacity as tidal air. The higher blood lactate indicates greater motivation. Psychological explanation on a similar basis is advanced for the frequent supremacy of the Negro in athletic competition.