The purpose of this study was to measure O2 consumption of nonexercising skeletal muscles (VO2nonex) at rest and after aerobic exercise and to investigate the stimulant factors of O2 consumption. In experiment 1, we measured the resting metabolic rate of the finger flexor muscles in seven healthy males by 31P-magnetic resonance spectroscopy during a 15 min arterial occlusion. In experiment 2, the VO2nonex of the finger flexor muscles was measured using near infrared continuous wave spectroscopy at rest, immediate postexercise, and 3, 5, 10, 15, and 20 min following a cycling exercise at a workload corresponding to 50% of peak pulmonary O2 uptake for 20 min. We also monitored deep tissue temperature in the VO2nonex measurement area and determined catecholamines and lactate concentrations in the blood at rest and immediate postexercise. VO2nonex at rest was 1.1 +/- 0.1 microM O2/S (mean +/- standard error) and VO2nonex after exercise increased 59.6 +/- 7.2% (p < 0.001) from the resting values. There were significant correlations between the increase in VO2nonex and the increase in epinephrine concentration (p < 0.01), and between the increase in VO2nonex and the increase in lactate concentration (p < 0.05). These results suggest that epinephrine and lactate concentrations are important VO2nonex stimulant factors.