Skeletal muscle V̇o2 kinetics by the NIRS repeated occlusions method during the recovery from cycle ergometer exercise

Near-infrared spectroscopy (NIRS) has been utilized as a noninvasive method to evaluate skeletal muscle mitochondrial function in humans, by calculating muscle V̇o2 (V̇o2m) recovery (off-) kinetics following short light-intensity plantar flexion exercise. The aim of the present study was to determine V̇o2m off- kinetics following standard cycle ergometer exercise of different intensities. Fifteen young physically active healthy men performed an incremental exercise (INCR) up to exhaustion and two repetitions of constant work-rate (CWR) exercises at 80% of gas exchange threshold (GET; MODERATE) and at 40% of the difference between GET and peak pulmonary V̇o2 (V̇o2p; HEAVY). V̇o2p and vastus lateralis muscle fractional O2 extraction by NIRS (Δ[deoxy(Hb+Mb)]) were recorded continuously. Transient arterial occlusions were carried out at rest and during the recovery for V̇o2m calculation. All subjects tolerated the repeated occlusions protocol without problems. The quality of the monoexponential fitting for V̇o2m off-kinetics analysis was excellent (0.93≤r2≤0.99). According to interclass correlation coefficient, the test-retest reliability was moderate to good. V̇o2m values at the onset of recovery were ~27, ~38, and ~35 times higher (in MODERATE, HEAVY, and INCR, respectively) than at rest. The time constants (τ) of V̇o2m off-kinetics were lower (P < 0.001) following MODERATE (29.1 ± 6.8 s) vs. HEAVY (40.8 ± 10.9) or INCR (42.9 ± 10.9), suggesting an exercise intensity dependency of V̇o2m off-kinetics. Only following MODERATE the V̇o2m off-kinetics were faster than the V̇o2p off-kinetics. V̇o2m off-kinetics, determined noninvasively by the NIRS repeated occlusions technique, can be utilized as a functional evaluation tool of skeletal muscle oxidative metabolism also following conventional cycle ergometer exercise.