Regional and Total Body Sweat Composition of Men Fed Controlled Diets

Abstract

Sweat was collected from acclimatized young men during work on a cycle ergometer in a temperate environment. The men were divided into two matched groups of six each and fed for 6 weeks either a diet of the type used for Project Gemini or a purified formula. Sweat was extracted from plastic-covered patches placed on the arm, back, and chest; collected in a plastic arm bag; and recovered from bath and laundry water. Sodium, nitrogen, and potassium were measured in all samples; in the total body sweat, these three and chloride, calcium, and magnesium were measured. There was considerable variation in the concentrations of the various constituents between the regional sites and the total body sweat. With the single exception of sodium, arm-bag sweat was the most concentrated; for all constituents measured, total body sweat was the least concentrated. The following factors were related: Sweat sodium and chloride were directly related to dietary intake; osmolality of arm-bag sweat varied directly with sodium concentration within and between dietary groups; and nitrogen concentration of total body sweat varied inversely with the volume of sweat lost in the constant 40-min work test. Although the concentrations were dissimilar, sodium contents of arm-bag and total body sweat were closely related (r = 0.83). This was not true of nitrogen and potassium levels. Thus, arm-bag sweat cannot be used to predict body losses of these components. The results suggest that variation among published total body sweat nitrogen data may be rationalized by consideration of sweat rate.