PURPOSE: This study investigated the impact of intensified training (IT) and carbohydrate (CHO) supplementation on resting and exercise-induced oxidative stress. METHODS: Male cyclists (n = 13, mean ± SD: age 25 ± 6 years; [Formula: see text] 72 ± 5 ml/kg/min) undertook two 9 day periods of endurance-based IT. In a counter-balanced, crossover and double-blinded study design, participants completed IT whilst ingesting high (H-CHO) or moderate (M-CHO) CHO beverages before (H-CHO: 24 g vs. M-CHO: 2 g), during (H-CHO: 60 g/h vs. M-CHO: 20 g/h) and after training sessions (H-CHO: 44 g vs. M-CHO: 10 g). Participants completed fasted performance trials without CHO on days 2, 6 and 10. Blood samples were taken before and immediately after exercise to assess plasma oxidative stress. RESULTS: Resting thiol (-SH) and catalase (CAT) activities decreased following 6 days of IT, independent of CHO condition [-SH (µM oxidised NADPH): H-CHO-14.0 ± 18.8, M-CHO-20.4 ± 20.3 and CAT (nmol/min/ml): H-CHO 12.5 ± 12.5, M-CHO 6.0 ± 4.5; all p < 0.05]. Resting total antioxidant capacity (TAC) was reduced after IT in M-CHO. All exercise bouts elicited significant increases in CAT, TAC, protein carbonylation (PC) and lipid hydroperoxides (LOOH), independent of CHO condition (p < 0.05). The magnitude of increase in PC and LOOH was greater on days 6 and 10 compared to day 2 in both conditions. CONCLUSIONS: Short-term IT caused reductions in resting antioxidant capacity in trained cyclists. Exercise-induced increases in PC and LOOH were exaggerated as a result of IT; however, these responses were independent of carbohydrate intake before, during and after the preceding IT sessions.
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