Purpose: The purpose of this investigation was to examine the effects of dehydration on the lactate threshold and performance time to exhaustion in women.
Methods: Seven moderately trained women (age = 23.6 +/- 1.6 yr) performed two graded exercise tests on separate occasions, once in a normally hydrated state (HY) and once in a dehydrated state (DE). Dehydration was achieved by a 45-min submaximal exercise the evening before testing, followed by a 12-h period of fluid restriction. VO2, VCO2, V(E), R-values, blood lactate, and catecholamine concentrations were measured at baseline and during each workload. Plasma volume and plasma osmolality were also determined. Body weight dropped significantly for the dehydrated trial (2.6 +/- 0.7%).
Results: There was a corresponding decrease in plasma volume measured (3.5 +/- 2.6%). The VO2max (3.1 +/- 0.3 L x min(-1) HY; 3.0 +/- 0.1 L x min(-1) DE) obtained was not significantly different between the hydration and dehydration trial. Plasma norepinephrine, epinephrine, and lactate concentrations were not significantly different at baseline or maximum intensity although epinephrine concentrations were higher for the dehydrated trial during submaximal workloads. Lactate concentrations were highly correlated with epinephrine (r = 0.95 HY; r = 0.97 DE). The lactate threshold occurred at a significantly lower relative percent of VO2max for the dehydrated trial (72.2 +/- 1.1% HY; 65.5 +/- 1.8% DE) as well as a lower absolute power output when compared with that in the hydrated trial. There was a significant decrease in time to exhaustion for the dehydrated trial (17.3 +/- 0.7 min HY; 16.3 + 0.7 min DE). Time to exhaustion for the dehydrated trial was correlated with the % VOmax at which the lactate threshold occurred (r = 0.74).
Conclusions: These data indicate that low levels of dehydration induced a shift in the lactate threshold, in part because of elevated epinephrine concentrations. This shift may have been one cause for the decrease in time to exhaustion for the dehydrated trial.