Water budget during ultra-endurance exercise

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Abstract
We examined water gains and water losses in a group of athletes after an ultra-endurance event. Thirteen male triathletes competed in a triathlon consisting of 21 km canoeing, 97 km cycling, and 42 km running. Water loss determinations included sweat rate (940 ± 163 g·h-1), urine output (41 ± 38 g·h-1), and respiratory water loss(88 ± 10 g·h-1). Water gain measurements included water intake (737 ± 137 g·h-1) and the water content of the food intake (10 ± 7 g·h-1), and we estimated the water of metabolism for carbohydrate (49 ± 5 g·h-1) and fat (41± 5 g·h-1) and the water released after glycogen utilization (104 ± 64 g·h-1). Total water gain averaged 940 ± 160 g·h-1, while the total water loss averaged 1069± 163 g·h-1. Body weight changed from 69.87 ± 7.14 kg before the race to 66.65 ± 6.75 kg after the race (-4.61 ± 2.94%). The sum of the exogenous water gains and the endogenous water gains(940 g·h-1) replaced almost 90% of the total water loss (1069 g·h-1). The difference (1334 g) represented a loss of about 1.9% of the initial body mass (69.87 kg). The exogenous water gains alone (747 g·h-1) replaced about 70% of the total water loss, and the difference represented a loss of over 4% of the initial body mass. Because of the nature of the endogenous sources of water gain, the total amount of water gain almost replaces the total amount of water loss (difference ≈ 12%) even in the presence of a reduction in body mass (>4%).

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