Endurance Performance After Modest Hypohydration Evoked By Prolonged Fluid Restriction And Exercise Or Diuretics

Abstract

Different dehydration methods may explain previous contrasting findings concerning the effect of modest hypohydration (2-3% body mass: BM) on endurance performance in a temperate environment. Greater performance decrements may be related to diuretics causing greater cardiovascular strain during exercise compared with fluid restriction and exercise. PURPOSE: To examine the effect of modest hypohydration evoked by different dehydration methods on endurance performance and cardiovascular function. METHODS: Seven males (mean ± SEM: age 25 ± 1 y; VO2peak 59 ± 3 mL·kg-1·min-1) completed three randomised trials prior to completing a time to exhaustion (TTE) at 70% peak power output on a cycle ergometer in temperate conditions (21°C, 61% RH). On the control trial (C) participants received water equal to 40 mL·kg·bm·d-1. To achieve hypohydration prior to the TTE, on one trial participants received 40 mg of the diuretic Furosemide (D) and on another trial completed exercise followed by 48 hours of fluid restriction (FR: 239 ± 129 mL·d-1). This exercise bout was also completed with fluid replacement on C and D. BM, plasma volume change (PV) and osmolality (POsm) were assessed pre and post these interventions. During the TTE heart rate (HR), stroke volume (SV), cardiac output (Q) and ratings of perceived exertion (RPE) were assessed. Data were analysed by repeated measures ANOVA and Post hoc Tukeys test. RESULTS: Prior to TTE, BM and PV were significantly decreased on D (-2.0 ± 0.3 and -9.5 ± 1.9%) and FR (-2.3 ± 0.1 and -10.2 ± 4.4%) compared with C (0.2 ± 0.3 and 3.1 ± 4.8%: P < 0.01). POsm was significantly greater on FR compared with D and C (FR, 299 ± 2; D, 293 ± 1; C, 286 ± 3 mOsmol·kg-1: P < 0.01). TTE was significantly decreased on D but not on FR compared with C (D, 17:51 ± 2:10; FR, 19:30 ± 2:40; C, 22:49 ± 2:35 min:sec: P < 0.05, ES = 0.41). Compared with C, HR was greater on D during the TTE (C, 167 ± 2; D, 173 ± 2 bpm: P < 0.01) and SV and Q were lower in the final minute of exercise on D and FR (P < 0.05). RPE was not significantly different between trials. CONCLUSIONS: These results show a detrimental effect for modest isotonic hypohydration evoked by diuretics, which may be related to greater cardiovascular strain, but no significant effect of hypertonic hypohydration evoked by exercise and fluid restriction on endurance performance in a temperate environment.