The Effects of Acute Dehydration on the Anaerobic Threshold During Incremental Cycle Ergometer Exercise.

Abstract

Much of the previous research concerning dehydration and performance has centered around prolonged submaximal work while seemingly little attention has been focused upon short term incremental exercise. Numerous investigators have suggested that dehydration may alter carbohydrate metabolism in muscle. Theoretically, altered glycolytic flux in exercising muscle could result in a change in the rate of blood lactate (La) accumulation, and thus shift the anaerobic threshold. Anaerobic threshold (AT(,La)) has been formally defined as the oxygen uptake (V(,O(,2))) at which there is a systematic increase in blood La. Additionally, the AT(,La) has been estimated from a nonlinear increase in expired ventilation (AT(,V(,E))) during incremental exercise. The purpose of this study was to investigate the effect of acute dehydration on the onset of AT(,La) during graded exercise. Six trained male subjects performed an incremental cycle ergometer test to exhaustion during which the work rate was increased by 30 watts every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every third minute during the test. Subjects were tested twice, once in a normally hydrated condition (N) and once in a thermally dehydrated condition(D). The treatment order was counter balanced, and tests were one week apart. Acute thermal dehydration was induced by intermittent sauna exposure. Subjects were dehydrated until they had lost 5% of their initial body weight. Blood La showed a trend towards higher concentrations across time in the D condition but the differences were not significant, F(1,5) = 1.40, p > .29, between the experimental conditions. However, the AT(,La) occurred at a significantly, t(5) = -2.02, p < .09, lower V(,O(,2)) during exercise in the D condition when compared to work in the N condition. The correlation between AT(,La) and AT(,V(,E)) in the N condition was r = -.51 (p < .30) while the relationship between the AT(,La) and AT(,V(,E)) in the D experiment was r = .16 (p < .77). These data suggest that acute dehydration may alter the AT(,La). Also, the low correlations between the AT(,La) and AT(,V(,E)) in both experimental treatments indicated that there may be factors other than blood La concentrations which affect respiratory control during incremental exercise.