Skeletal muscle V<scp>o</scp>₂kinetics by the NIRS repeated occlusions method during the recovery from cycle ergometer exercise

Abstract

Near-infrared spectroscopy (NIRS) has been utilized as a noninvasive method to evaluate skeletal muscle mitochondrial function in humans, by calculating muscle V̇o₂ (V̇o₂<i>m</i>) recovery (off-) kinetics following short light-intensity plantar flexion exercise. The aim of the present study was to determine V̇o₂<i>m</i> 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 (V̇o₂<i>p</i>; HEAVY). V̇o₂<i>p</i> 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 V̇o₂<i>m</i> calculation. All subjects tolerated the repeated occlusions protocol without problems. The quality of the monoexponential fitting for V̇o₂<i>m</i> off-kinetics analysis was excellent (0.93≤<i>r</i>²≤0.99). According to interclass correlation coefficient, the test-retest reliability was moderate to good. V̇o₂<i>m</i> 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 V̇o₂<i>m</i> off-kinetics were lower (<i>P</i> < 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 V̇o₂<i>m</i> off-kinetics. Only following MODERATE the V̇o₂<i>m</i> off-kinetics were faster than the V̇o₂<i>p</i> off-kinetics. V̇o₂<i>m</i> 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.<b>NEW & NOTEWORTHY</b> This is the first study in which muscle V̇o₂ 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 V̇o₂ 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.