[Methodological studies on estimating the loss of sodium, potassium, calcium and magnesium exemplified by a 10-km run]

An estimation of the electrolytic losses through the skin was evaluated in a run over a distance of 10 km on a 400 m track. Na, K, Ca and Mg excreted by the skin were collected in standardised clothes and thereafter washed out. The remaining electrolytes on the skin were collected by washing the body with deionized water. In addition the concentrations of hormones and metabolites in blood before and after the race were measured. Mean ambient temperature and relative humidity amounted to 21 degrees C and 35%, respectively. The mean performance was 40.5 min. and the average body weight loss was 1.45 kg (1.95% of body weight). The only significant changes in the serum concentrations were the increases of free fatty acids and glycerol. This can be explained, together with a slight increase of glucose and a decrease of insulin, by a higher sympathoadrenergic activity. In the mean 20 mg calcium, 5 mg magnesium, 200 mg potassium and 800 mg sodium were lost by the skin per kg body weight loss. These values compared well with corresponding data found in literature. The described method can therefore be proposed for further experiments.