Tapering can be an effective way of enhancing performance after a period of intensive training, but the mechanisms for this ergogenic effect are unclear. It was hypothesized that overload training will increase oxidative stress through an accumulative effect of repeated high-intensity exercise, whereas tapering will improve the antioxidant defense system and alleviate oxidative stress. Purpose: To study the oxidative stress response to overload training and tapering. Methods: A group of eight well-trained male endurance athletes (30 +/- 6 yr; 73 +/- 13 kg; 64 +/- 6 mL/kgmin performed two 4-wk periods of training in a crossover design. Each period included a 2-wk build-up phase followed either by 2 wk of training at the same load (control) or by a week with a 40% increase in training load (overload) preceding a week with a 60% reduction in training load (taper). Performance was monitored through weekly 15-min cycling time trials preceded by a 45-min preload at 70% Wmax. Blood samples were taken before and after the time trials and analyzed for oxidatively modified heme (OxHm), methemoglobin (metHb), and glutathione redox status. Results: Cycling time trials induced significant postexercise increases in levels of OxHm (+3.8%; P < 0.001) and oxidized glutathione (GSSG: +13.9%; P < 0.05) and decreases in metHb (-12.1%; P < 0.001), reduced glutathione (GSH: -14.4%; P < 0.001), and GSH/GSSG (-29.7%; P < 0.001). Tapering was shown to significantly increase performance (+4.9%; P < 0.05). Training modifications did not influence resting levels or exercise-induced changes of markers of oxidative stress. Conclusion: A short period of tapered training improves performance but does not seem to be associated with substantial changes in exercise-induced oxidative stress.
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