Interaction Of 4% Hypohydration And 3,048 M Altitude On Aerobic Exercise Performance

Abstract

Body water deficits (3-4% of body weight) degrade aerobic exercise performance in temperate and hot environments. Hypoxia will induce body water deficits (hypohydration, HYP), however, the effects of HYP on aerobic exercise performance at high altitude has not been reported. PURPOSE: Determine effects of HYP (∼4% body weight loss) on aerobic exercise performance at sea-level (SL) and high-altitude (ALT, 3,048 m). We hypothesized that HYP and ALT would each degrade exercise performance relative to SL-euhydrated (EUH) conditions and combining HYP and ALT would further degrade performance more than one stressor alone. METHODS: Seven men (25 ± 7 yr; 82 ± 11 kg; mean ± SD) completed 4 separate experimental trials. Trials were: a) SL- EUH; b) SL-HYP; c) ALT-EUH; and d) ALT-HYP. The day before each trial, subjects walked for ∼2.5 h in the heat (50°C) either with (EUH) or without (HYP) fluid replacement. In HYP, exercise continued until 4% of body weight was lost. Subjects maintained hydration status overnight and the following morning entered a hypobaric chamber where they completed submaximal exercise (cycle ergometry) at 45% VO2max (20 min) and 60% VO2max (10 min) immediately followed by a 30-min performance time-trial (TT) at an ambient temperature of 27°C. Performance was assessed by the total amount of work (kJ) completed during the TT. RESULTS: Total TT work (kJ, mean ± SD) for each trial was: SL-EUH (334 ± 64), SL-HYP (278 ± 87, p<0.05 vs. SL-EUH), ALT-EUH (293 ± 33, p=0.06 vs. SL-EUH), and ALT-HYP (227 ± 95, p<0.05 compared to the other 3 trials). The change in performance, relative to the SL-EUH, trial was -18.6 ± 12.2% for SL-HYP, -11.0 ± 10.4% for ALT-EUH, and -33.7 ± 22.3% for ALT-HYP. Individual performance changes, relative to SL-EUH, demonstrated that 6/7 volunteers did worse during ALT-EUH, while 7/7 subjects did worse during SL-HYP and ALT-HYP. The total work during ALT-HYP was significantly lower (P<0.05) vs. the other trials. CONCLUSION: These data support the hypothesis that moderate body water deficits and high-altitude degrade aerobic performance, and that when these two stressors are combined, aerobic performance is degraded in an additive manner. These findings demonstrate the importance of maintaining euhydration on sustaining aerobic exercise performance at high-altitude. Author‘s opinion: not govt. policy