Skeletal muscle V̇O 2 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 (V)over dotO(2) ((V)over dotO(2)m) recovery (off-) kinetics following short light-intensity plantar flexion exercise. The aim of the present study was to determine (V)over dotO(2)m 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 (V)over dotO(2) ((V)over dotO(2)p; HEAVY). (V)over dotO(2)p and vastus lateralis muscle fractional O-2 extraction by NIRS (Delta[deoxy(Hb+Mb)]) were recorded continuously. Transient arterial occlusions were carried out at rest and during the recovery for (V)over dotO(2)m calculation. All subjects tolerated the repeated occlusions protocol without problems. The quality of the monoexponential fitting for (V)over dotO(2)m off-kinetics analysis was excellent (0.93 <= r(2)<= 0.99). According to interclass correlation coefficient, the test-retest reliability was moderate to good. (V)over dotO(2)m 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 (tau) of (V)over dotO(2)m 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 (V)over dotO(2)m off-kinetics. Only following MODERATE the (V)over dotO(2)m off-kinetics were faster than the (V)over dotO(2)p off-kinetics. (V)over dotO(2)m 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. NEW & NOTEWORTHY This is the first study in which muscle (V)over dotO(2) recovery kinetics, determined noninvasively by near-infrared spectroscopy (NIRS) by utilizing the repeated occlusions method, was applied following standard cycle ergometer exercise of different intensities. The results demonstrate that muscle (V)over dotO(2) recovery 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, overcoming significant limitations associated with the traditionally proposed protocol.