creasing the power-to-mass ratio. This study examined the effects of a reduction in body mass attributable to unreplaced sweat losses on simulated cycling hill-climbing performance in the heat. METHODS: Eight well-trained male cyclists (mean +/- SD: 28.4 +/- 5.7 yr; 71.0 +/- 5.9 kg; 176.7 +/- 4.7 cm; VO2peak: 66.2 +/- 5.8 mL x kg(-1) [...]

The purpose of this study was to identify and to compare the effects of ingesting liquids during a 16-km military march under moderate environmental conditions. Twenty-six volunteer male subjects were randomly divided into two groups. Group GW received water (n=12), and group GP received an electrolytic carbohydrate solution (n=14). Blood and urine samples were obtained [...]

During exercise, sweat output often exceeds water intake, producing a water deficit or hypohydration. The water deficit lowers both intracellular and extracellular fluid volumes, and causes a hypotonic-hypovolemia of the blood. Aerobic exercise tasks are likely to be adversely effected by hypohydration (even in the absence of heat strain), with the potential affect being greater [...]

This study determined whether 1) exhaustion from heat strain occurs at the same body temperatures during exercise in the heat when subjects are euhydrated as when they are hypohydrated, 2) aerobic fitness influences the body temperature at which exhaustion from heat strain occurs, and 3) curves could be developed to estimate exhaustion rates at a [...]

The effect of hydration status on plasma vasopressin release was studied in six healthy volunteers undergoing a 15-min bicycle ergometer exercise. The hydration states were dehydration, produced by a 14-h abstinence from fluids, euhydration, and hyperhydration caused by drinking 20 ml kg-1 water 2 h before the exercise. The exercise load was individually adjusted to [...]

This study examines the effect of the initial state of hydration on hormone responses to prolonged exercise in the heat. Five subjects at two initial hydration levels (hypohydrated and hyperhydrated) were exposed to a 36 degrees C environment for 3 h of intermittent exercise. During exercise, the subjects were either fluid-deprived, or rehydrated with water [...]

During exercise, increased capillary hydrostatic pressure caused by elevation of arterial pressure produces plasma volume shifts from the vascular space to the interstitial fluids. Following a rapid efflux of vascular fluid within minutes of exercise, there is very little further reduction in plasma volume during long-term exercise, suggesting protective mechanisms against loss of circulating blood [...]

Dehydration leads to the aggravation of gastrointestinal (GI) complaints during exercise. The aim of this study was to examine the effect of dehydration on various GI parameters during strenuous exercise. Ten healthy well-trained men were investigated in dehydrated and in euhydrated conditions. Dehydration took place before the experiments using a dehydration regimen in a sauna [...]

Three groups of five men each were dehydrated overnight in the heat (115 degrees F) on two occasions (D1 and D2) to approximately 5.5% of their starting body weight. During the 3-week period between D1 and D2, one group (AC) was acclimatized to heat and physically conditioned, the second group (C) was physically conditioned and [...]

Dehydration refers both to hypohydration (dehydration induced prior to exercise) and to exercise-induced dehydration (dehydration that develops during exercise). The latter reduces aerobic endurance performance and results in increased body temperature, heart rate, perceived exertion, and possibly increased reliance on carbohydrate as a fuel source. Although the negative effects of exercise-induced dehydration on exercise performance [...]