Effects Of Training Status On Oxidative Stress After Exercise Induced Dehydration

Abstract

INTRO: Heat stress and dehydration have been shown to increase oxidative stress, both passively and during exercise. However, the degree of oxidative stress induced in these conditions may be related to differences in training status between individuals. PURPOSE: The purpose of this study was to compare the oxidative stress response to exercise in the heat with or without dehydration between trained cyclists and sedentary individuals. METHODS: 7 male trained cyclists (TR) and 7 apparently healthy untrained individuals (UT) (power output (W) @ lactate threshold (LT): 197 ± 18 W and 100 ± 13 W) completed 90 min at 95% LT (SP) followed by a 5 km time trial (TT) in four different randomized conditions: heat dehydration (HD), heat euhydration (HE), moderate dehydration (MD) and moderate euhydration (ME). All trials were completed in a controlled environmental chamber (heat: 33.9 + 0.9°C; moderate: 23.0 + 1.0°C). Venous blood was obtained pre and post trial and analyzed for oxidized (GSSG) and total (TGSH) glutathione, thiobarbituric acid reactive substances (TBARS), and monocyte heat shock protein (mHSP) 72 concentration. RESULTS: TR subjects experienced an increase in GSSG formation during both dehydration conditions while euhydration attenuated GSSG formation (p < 0.01), with heat exposure having no additional influence. Contrary to these finding, UT subjects did not exhibit a dependence on hydration, whereby GSSG formation increased as a result of exercise regardless of environment or hydration status (P < 0.05). mHSP72 concentration was increased as a result of exercise, regardless of environment or hydration status in both groups (p 0.05). Performance was diminished during only the HD condition and to a similar extent in TR and UT, with less distance covered during SP (p < 0.01), decreased PO during TT (p < 0.05), and increased time to completion for the TT (p < 0.05). CONCLUSION: Dehydration resulted in an augmented GSSG formation during prolonged cycling in TR but not in UT subjects. This is likely due to the positive adaptations in the antioxidant defence systems exhibited by trained individuals.