Near-infrared spectroscopy (NIRS) provides a simple and reliable measure of skeletal muscle oxidative capacity; however, its relationship to aerobic fitness and sex are unclear. We hypothesized that NIRS-derived oxidative capacity in the vastus lateralis (VL) and medial gastrocnemius (MG) would be correlated to indices of aerobic fitness and independent of sex. Twenty-six participants (13 males, 13 females) performed ramp- and step-incremental tests to volitional exhaustion on separate days to establish maximal oxygen uptake (V̇O2max), peak power output (PPO), lactate threshold (LT), gas exchange threshold (GET), respiratory compensation point (RCP), and maximal fat oxidation (MFO). Data were normalized to lean body mass to account for sex-based differences in body composition. Exercise tests were preceded by duplicate measurements of NIRS-derived oxidative capacity on the VL and MG muscles (i.e., repeated arterial occlusions following a brief set of muscle contractions). Skeletal muscle oxidative capacity for the VL (mean±SD: 21.9±4.6s) and MG (22.5±6.1s) were similar but unrelated (r2=0.03, p=0.39). Skeletal muscle oxidative capacity for the VL, but not the MG (p>0.05 for all variables), was significantly correlated with V̇O2max (r2=0.24; p=0.01), PPO (r2=0.23; p=0.01), LT (r2=0.23; p=0.01), GET (r2=0.23; p=0.01), and RCP (r2=0.27; p=0.006). MFO was not correlated with VL or MG skeletal muscle oxidative capacity (p>0.05). Females (54.9±4.5mL/kg LBM/min) and males (56.0±6.2mL/kg LBM/min), matched for V̇O2max (p=0.62), had similar NIRS-derived oxidative capacities for VL (20.7±4.4s vs. 23.2±4.6s; p=0.18) and MG (24.4±6.8s vs. 20.5±4.8; p=0.10). Overall, NIRS-derived skeletal muscle oxidative capacity in VL is indicative of aerobic fitness and independent of sex in humans.