Effects of exercise intensity on postexercise oxygen consumption of the vastus lateralis

Postexercise muscle oxygen consumption (mV̇o₂) rate may contribute to understanding responses to and recovery from exercise. To measure postexercise mV̇o₂ of the vastus lateralis (VL) muscle after various exercise intensities using near-infrared spectroscopy (NIRS). Twenty healthy individuals, 18-35 yr old, participated in two testing sessions. An NIRS device was placed on the belly of the VL to measure differences in oxygenated and deoxygenated hemoglobin (Hb_diff). Electrodes were placed proximally and distally to the NIRS device, and a cuff capable of rapid inflation was placed on the upper leg. mV̇o₂ at rest was assessed as the slope of the Hb_diff signal (% s^-1) during 3 × 30-s cuff inflations at 300 mmHg. Neuromuscular electrical stimulation (NMES) was applied for 30 s, and mV̇o₂ was assessed 5 min later. Participants performed maximal and submaximal (60% V̇o_2peak) cycling tests 1 wk apart, and mV̇o₂ was assessed 15 min later. Desaturation slopes (% s^-1) were calculated in Hb_diff signals to measure mV̇o₂. On average, mV̇o₂ 5 min post-NMES was 1.8-fold higher compared with resting (P < 0.001). mV̇o₂ was 4.2-fold and 2.7-fold higher 15 min after maximal and submaximal cycling, respectively, compared with resting (both P < 0.001). Blood lactate was elevated 10 min after maximal (10 ± 3 mmol/L) and submaximal (4 ± 3 mmol/L) cycling (both P < 0.001). Muscle metabolism remained highly elevated 15 min after cycling exercise. NIRS-based mV̇o₂ may have value as an indicator of postexercise muscle metabolism.NEW & NOTEWORTHY We found that the muscle oxygen consumption rate 15 min after cycling exercise remained three- to fourfold higher than at rest. Higher-intensity exercise resulted in higher postexercise muscle oxygen consumption despite having the same total work during exercise. The detected elevations in muscle metabolism 15 min postexercise are comparable with those observed during light to moderate intensity exercise. Monitoring postexercise muscle metabolism may have practical applications for training and rehabilitation.