Abstract des Autors

21 experienced runners were studied during a marathon race to ascertain whether either depletion of energy substrate or rise in body temperature, or both, contribute to late-race slowing of running pace. 7 runners drank a glucose/electrolyte (GE) solution ad libitum throughout the race; 6 drank water and 8 drank the GE solution diluted 1:1 with water. Although average running speeds for the 3 groups were not significantly different during the first 2/3 (29 km) of the race, rectal temperature was significantly higher and reduction of plasma volume was greater in runners who replaced sweat losses with water. During the last 1/3 of the race, the average running pace of the water-replacement group slowed by 37.2; the pace slowed by 27.9 in the 8 runners who replaced sweat loss with GE diluted 1:1 with water (1/2 GE) and 18.2 in runners who replaced fluid loss with full-strength solution (GE). 11 runners (5 water group, 4 1/2 GE group and 2 GE group) lapsed into a walk/run/walk pace during the last 6 miles of the race. 10 of these had a rectal temperature of 39 deg C or greater after 29 km of running, and plasma volume was reduced by more than 10. Only 1 runner among those who ran steadily throughout the race had such an elevation of temperature and reduction of plasma volume. A significant reduction in plasma glucose concentration was present in 5 of the 11 walk/run/walk subjects and in none of those who rand steadily. Thus, late-race slowing results from high body temperature, diminished plasma volume and low blood sugar.