Purpose: To evaluate the effect of different fractions of inspired oxygen (FIO2) on oxidative stress during a high-intensity interval workout in trained endurance athletes residing at altitude. Methods: Subjects (N = 19) were trained male cyclists who were residents of moderate altitude (1800-1900 m). Testing was conducted at 1860 m (PB 610-612 torr, PIO2 ~128 torr). Subjects performed three randomized, single-blind trials consisting of a standardized interval workout (6 x 100 kJ) while inspiring a medical-grade gas with FIO2 0.21 (PIO2 ~128 torr), FIO2 0.26 (PIO2 ~159 torr), and FIO2 0.60 (PIO2 ~366 torr). Serum lipid hydroperoxides (LOOH) and whole-blood reduced glutathione (GSH) were measured 60 min preexercise and immediately postexercise, and analyzed using standard colorimetric assays. Urinary malondialdehyde (MDA) and 8-hydroxydeoxyguanosine (8-OHdG) were measured 24 h preexercise and 24 h postexercise, and analyzed via HPLC and ELISA, respectively. Results: Compared with the control trial (FIO2 0.21), total time (min:s) for the 100-kJ work interval was faster (5% in FIO2 0.26; 8% in FIO2 0.60 (P < 0.05)) and power output (W) was higher (5% in FIO2 0.26, 8% in FIO2 0.60 (P < 0.05)) in the supplemental oxygen trials. There was a significant pre- versus postexercise main effect (P < 0.05) for LOOH and GSH; however, there were no significant differences in LOOH or GSH between the FIO2 trials. MDA and 8-OHdG were unaffected by either the interval training session or FIO2. Conclusion: Supplemental oxygen used in conjunction with high-intensity interval training at altitude ("live high + train low via supplemental O2" (LH + TLO2)) results in a significant improvement in exercise performance without inducing additional free radical oxidative stress as reflected in hematological and urinary biomarkers.
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