Exercise and Water-Electrolyte Balance

摘要

After oxygen, water becomes of prime importance for maintaining the health and well being of the human organism. Healthy people can live 3 to 4 weeks without food but less than 18 days without water (Wolf, 1958); the exact time depends upon the rate of the negative water balance. Physical exercise exerts a powerful influence upon the dynamic body-fluid and electrolyte equilibrium. In most circumstances exercise is associated with an increase in body temperature and the effects of the various degrees of heating must be considered when fluid and electrolyte shifts are discussed. If sweating occurs and the water and electrolytes are not adequately replaced-a common occurrence-the compensatory reactions to water depletion must be added to those of heat in determining the mechanisms involved in the maintenance of fluid-electrolyte homeostasis during exercise. In this review the term exercise refers to the movement of the body in the upright position. The profound effects of immobilization, changes in body position, and simulated weightlessness on water and electrolyte balance are beyond the scope of this paper: there has been a renewed interest in these three areas by workers in space medicine and nutrition. There are large gaps in our knowledge of the nutritional aspects of water and electrolyte balance associated with various levels of physical exercise in normal healthy people. I will attempt to briefly summarize the normal water and electrolyte distribution, followed by a discussion of the effects, singly and in combination, of exercise, heat, and hypohydration on the water and electrolyte balance in general, the resultant changes in circulatory and renal functions, and the subsequent effects on thirst and drinking in particular. The effects of water depletion upon physical performance will also be discussed with some practical remedial suggestions. The term hypohydration refers to the state of diminished water content in the body; normohydration to the normal, ad libitum water balance; and hyperhydration to an increase in water content above normal.