Post-exercise rehydration in man
The experiments of this thesis have confirmed and widened much of the previous knowledge concerning recovery from moderate levels of exercise-induced dehydration. A protocol for inducing sweat loss and monitoring recovery has been established and verified, and a reliable methodology for the collection and analysis of whole body sweat developed. In general, intermittent exercise at an intensity corresponding to 60% 2max was undertaken in a warm (approximately 34°C), humid (60-70% rh) environment. Subjects were dehydrated by approximately 2% of their body mass and rehydrated with a fluid volume equivalent to 3% of their body mass. The composition of the rehydration fluid was determined by the aims of each particular study. By systematically varying the sodium concentration of rehydration fluids, the importance of sodium consumption for the retention of the ingested water was confirmed. However, when the sodium intake was extremely high (206 mmol from consumption of a 100 mmol l-1Na+ drink), fluid balance restoration was achieved at the expense of an excess of sodium retention and an increased potassium excretion. This effect on potassium levels must be considered to be undesirable for anything other than the short term situation. Alcohol consumption in the form of beer is the beverage of choice of many individuals following exercise but is frequently advised against because of the diuretic actions of the alcohol. However, this thesis demonstrates that the diuretic effect of alcohol is substantially blunted when alcohol is consumed following a moderate level of hypohydration induced by exercising in the heat; there appears to be no difference in recovery, in terms of fluid balance, from dehydration whether the rehydration beverage is alcohol-free or contains up to 2% alcohol and sufficient volume is consumed.