Reduced serum concentrations of reactive oxygen and nitrogen species following strenuous exercise in the heat are not associ-ated with an upregulation in serum antioxidative capacity

Abstract

Introduction: Reactive oxygen and nitrogen species (RONS) are produced as a response to exercise and play a part in guiding the adaptive response to physical training. Exercise in the heat has been shown to further increase accumulation of RONS in systemic circulation; however, a high antioxidative response or heat acclimatization mechanisms could attenuate this response. In a previous study, we found reduced RONS concentrations in trained athletes following strenuous cycling in the heat. Therefore, this secondary analysis assessed whether these reduced RONS serum concentrations are induced by an increased serum antioxidant capacity. Methods: Twelve male cyclists (V̇O2peak: 60 ± 4 ml ∙ kg-1 ∙ min-1) completed a 60-minute constant workload trial (55% peak power output, ambient temperature 30.4 ± 0.6°C) with and without ice vest in a randomized order. The core body temperature (Tcore) was measured by an ingestible capsule. Blood samples were collected before and after each trial to determine superoxide dismutase (SOD) and catalase (CAT) activity, total antioxidant capacity (TAC) and RONS. Due to the absence of between-group differences, data of both conditions were pooled. Results: Tcore statistically increased (p < 0.001) over the experimental trials (+6.0 ± 1.6%, effect size (ES) = 5.6). Concentrations of RONS (-17.2 ± 15.5%, p < 0.001, ES = 1.0) and TAC (-8.9 ± 22.9%, p = 0.04, ES = 0.7) statistically decreased, while the activity of CAT (+15.5 ± 84.0%, p = 0.90, ES = 0.04) and SOD (+9.2 ± 58.7%, p = 0.98, ES = 0.01) remained unchanged. Conclusions: Reduced serum RONS concentrations after strenuous cycling in the heat were not associated with upregulation of serum antioxidant capacity in trained athletes. The prooxidant-antioxidant balance may rather be regulated at a myocellular level and should be further assessed in future studies.

Keywords

• antioxidants
• catalase
• reactive oxygen species
• superoxide dismutase
• sports medicine
• total antioxidant capacity