Antioxidant supplementation blunts the proteome response to 3 weeks of sprint interval training preferentially in human type 2 muscle fibres

Sprint interval training (SIT) is a time-efficient type of endurance training that involves large type 2 muscle fibre recruitment. Effective antioxidant supplementation may mitigate positive training adaptations by limiting the oxidant challenge. Our aim was to test whether SIT affects type 2 more than type 1 muscle fibres, and whether the muscular training response is mitigated by antioxidant treatment. Young men performed three weekly SIT sessions (4-6 × 30 s all-out cycling) for 3 weeks while treated with antioxidants (vitamin C, 1 g day^-1; vitamin E, 235 mg day^-1) or placebo. Vastus lateralis biopsies were taken to measure (i) activation of genes for reactive oxygen/nitrogen species (ROS) sensors and inflammatory mediators with quantitative RT-PCR and (ii) fibre type-specific proteome adaptations using MS-based proteomics. Vitamin treatment decreased the upregulation of genes for ROS sensors and inflammatory regulators during the first SIT session. The 3 weeks of SIT caused generally larger proteome adaptations in type 2 than in type 1 fibres, and this included larger increases in abundance of proteins involved in mitochondrial energy production. Vitamin treatment blunted the SIT-induced proteome adaptations, whereas it did not affect the training-induced improvement in maximal cycling performance. In conclusion, (i) the large type 2 fibre recruitment and resulting proteome adaptations are instrumental to the effectiveness of SIT and (ii) antioxidant supplementation counteracts positive muscular adaptations to SIT, which would blunt any improvement in submaximal endurance performance, whereas it does not affect the improvement in maximal cycling performance, where O₂ delivery to muscle would be limiting. KEY POINTS: Sprint interval training (SIT) is a time-efficient type of endurance training that involves large recruitment of fast-twitch muscle fibres. Treatment with antioxidants may mitigate the positive effects of endurance training. Fibre type-specific proteomics performed on muscle biopsies obtained from young men before and after 3 weeks of SIT showed larger training effects in fast- than in slow-twitch fibres. Antioxidant treatment in the form of vitamin C and E pills counteracted the positive muscular adaptations to the 3 weeks of SIT. These results increase our understanding of why SIT is an effective endurance training regime and provide further evidence against the common belief that antioxidant supplements are beneficial in a physical exercise context.