Implications of active lifestyles and environmental factors for water needs and consequences of failure to meet those needs.

Heat stress and exercise increase water loss from the body, primarily in the form of sweat. For some occupational groups, including miners, construction workers in hot climates, soldiers, and some athletes, daily water losses can reach 10-12 L. These losses must be replaced on a daily basis to maintain functional capacity. Both hyperhydration and hypohydration will, if sufficiently severe, impair all aspects of physiological function. Tests of strength and power are largely unaffected by dehydration of up to about 2%-4% of body mass. However, decrements in the performance of endurance tests may occur at these levels, especially in warm environments. Body water deficits, if sufficiently severe, also have adverse effects on measures of mood and on some elements of cognitive function and result in an increased subjective rating of the perception of effort. Beverages consumed during exercise can provide carbohydrates and electrolytes that may be beneficial in some situations; however, drinking in volumes required to match sweat loss may cause gastrointestinal discomfort that will generally impair performance.