Abstract
The benefits of physical activity (PA) and the negative impacts of sedentary time (SED) on both short- and long-term health in youth are well established. However, uncertainty remains about how PA and SED jointly influence maximal oxygen uptake ([Formula: see text]). Therefore, the aim of this study was to determine the joint influence of PA and SED on [Formula: see text] using compositional analyses. 176 adolescents (84 girls, 13.8 ± 1.8 years) completed an incremental ramp test and supramaximal validation bout on a cycle ergometer, with PA and SED recorded for seven consecutive days on the right hip using a ActiGraph GT3X accelerometer. Time spent in Sleep, SED, light, moderate and vigorous PA was analysed using a compositional linear regression model. Compositions with 10 minutes more time in vigorous PA (> 27.5 mins⋅day-1) compared to the average 17.5 mins⋅day-1 were associated with a + 2.9% - 11.1% higher absolute and scaled [Formula: see text] whilst compositions with less (> -10 mins⋅day-1) VPA were associated with a reduced absolute and allometrically scaled [Formula: see text] (-4.6% - 24.4%). All associations were irrespective of sex, maturity, and training status. The proportion of time spent sedentary had little impact on absolute and scaled [Formula: see text] (0.01-1.98%). These findings therefore highlight that intensity of PA may be of greater importance for increases in [Formula: see text] than reductions in SED and should be incorporated into future intervention designs.