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FLUID REPLACEMENT AND HEAT STRESS
damage. Plasma renin activity was measured in the men before they arose in the morning and again before the noon meal.
Table 10-1 shows average values for total body K+, urine K+, and K+ from clothing eluates for the subjects studied in both hot and cool weather. In the six subjects studied during training in hot weather, the potassium deficit measured on day 4 averaged 348 mEq, and on day 11 it averaged 463 mEq (Knochel, 1977a; Knochel et al., 1972). The maximum deficits ranged between 370 and 572 mEq. In two men, the maximum deficit appeared on day 4, and in one man it appeared on day 18; in the remainder of the men it occurred on day 11. The average maximum deficit was 510 mEq. Total body potassium as a function of lean body mass fell from 52.2 to 42.5 mEq/kg, thus suggesting a reduction of intracellular muscle potassium content. Thereafter, total body potassium rose during successive weeks, so
Table 10-1 Potassium as Measured in Hot and Cool Weather
a In cool weather, 42K was not availabel for the 18 day study.
b Average of 5 subjects only.
that by week 5 the amount of potassium restored was about 200 mEq. The value of 42K per lean body mass was the same upon completion of training as it was during the first measurement. Potassium deficiency, defined as a reduction of 42Ke, did not occur during training in the winter. In the men who trained in the winter, total body potassium steadily increased from an initial value of 3,330 mEq to a final value of 3,716 mEq. When values for total body potassium over lean body mass were matched, there was a rise