Effects of exercise intensity on post-exercise oxygen consumption of the vastus lateralis.

Post-exercise muscle oxygen consumption rate (mVO₂) may contribute to understanding responses to and recovery from exercise. Purpose: To measure post-exercise mVO₂ of the vastus lateralis (VL) muscle after various exercise intensities using near-infrared spectroscopy (NIRS). Methods: Twenty healthy individuals, 18-35 years old, participated in two testing sessions. A 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. mVO₂ at rest was assessed as the slope of the Hb_diff signal (% s^-1) during 3 x 30 second cuff inflations at 300 mmHg. Neuromuscular electrical stimulation (NMES) was applied for 30 seconds, and mVO₂ was assessed 5 minutes later. Participants performed maximal and submaximal (60% VO₂peak) cycling tests 1 week apart, and mVO₂ was assessed 15 min later. Desaturation slopes (% s^-1) were calculated in Hb_diff signals to measure mVO₂. Results: On average, mVO₂ 5 minutes post-NMES was 1.8-fold higher compared to resting (p < 0.001). mVO₂ was 4.2-fold and 2.7-fold higher 15 minutes after maximal and submaximal cycling, respectively, compared with resting (both p < 0.001). Blood lactate was elevated 10 minutes after maximal (10 ± 3 mmol/L) and submaximal (4 ± 3 mmol/L) cycling (both p < 0.001). Conclusions: Muscle metabolism remained highly elevated 15 minutes after cycling exercise. NIRS-based mVO₂ may have value as an indicator of post-exercise muscle metabolism.