Purpose: The determinants of aerobic capacity are oxygen delivery by the cardiopulmonary system and oxygen extraction by the skeletal muscles. However, the impact of the oxygen extraction capacity of the skeletal muscle is unclear. This study aimed to examine the associations between aerobic capacity; muscle strength, endurance, mass, and quality; and oxygen extraction capacity. Methods: Twenty-seven healthy young men (mean age, 20.7 +- 0.8 years; body mass index, 21.6 +- 3.2 kg m-2) were recruited. The following parameters were determined: peak work rate (WR) and oxygen uptake (VO2) corrected for body mass using the cardiopulmonary exercise testing; muscle strength and endurance using isokinetic muscle testing; muscle mass using bioelectrical impedance; muscle quality (muscle echo intensity) using an ultrasound imaging device, and muscle oxygen extraction rate (MOER) using near-infrared spectroscopy. Multiple regression analysis was performed using WR/kg peak and VO2/kg peak as dependent variables and each assessment index as an independent variable. Results: Multiple regression analysis with WR/kg peak as the dependent variable resulted in the adoption of SMI (ß 5 =0.41, P 5 0.036), muscle echo intensity (ß 5 =0.45, P 5 0.012) and DMOER (ß 5 0.73, P < 0.001) as significantly associated factors. Multiple regression analysis with VO2/kg peak as the dependent variable resulted in DMOER (ß 5 0.65, P 5 0.001) being adopted as a significantly associated factor. Conclusion: These findings suggest that muscle oxygen extraction rate is associated with aerobic capacity. MOER is a useful indicator because it is not affected by body mass.  Kulcsszavak: aerobic capacity, muscle oxygen extraction rate, near-infrared spectroscopy, peak work rate, skeletal muscle