The Thiol Oxidation State of Albumin Is Associated With Training Load Across an Australian Football Pre-Season

Australian football is a demanding contact sport where high training loads during the pre-season have been identified as a potential cause of non-contact injuries. The level of thiol-oxidised albumin, a marker of oxidative stress, might be related to the training load, and thus could be used to indirectly quantify the impact of training loads upon an athlete. The aim of this study was to investigate whether the level of thiol-oxidised albumin was affected by the pre-season training load in a team of professional Australian Football League (AFL) athletes and compare the effect of lower pre-season training loads caused by COVID-19 restrictions on the level of thiol-oxidised albumin. Forty-five participants collected daily dried blood spots in the morning prior to each training session to measure thiol-oxidised albumin using a novel methodology (OxiDx). Training load, which was operationally defined as the total distance covered during training as well as distance at certain velocities, and change of direction (COD), was measured using global positioning units. There was an association (R² = 0.12) between the level of thiol-oxidised albumin with; (1) total distance covered (p  < 0.0001), (2) distance covered at 10-20 km/h (p  < 0.0001) and 20-25 km/h (p = 0.0082) and (3) COD running (p = 0.0025). Training loads and the level of thiol-oxidised albumin were highest in the early pre-season and lowest at the conclusion of the pre-season, when training loads were reduced as a consequence of COVID-19. The measurement of the level of thiol-oxidised albumin may provide a means to indirectly quantify the impact of training loads upon an athlete, especially given the simplicity of the OxiDx methodology for fingertip blood sample collection.