Methodological considerations on near-infrared spectroscopy derived muscle oxidative capacity

Abstract

Abstract Purpose Different strategies for near-infrared spectroscopy (NIRS)-derived muscle oxidative capacity assessment have been reported. This study compared and evaluated (I) approaches for averaging trials; (II) NIRS signals and blood volume correction equations; (III) the assessment of vastus lateralis (VL) and tibialis anterior (TA) muscles in two fitness levels groups. Methods Thirty-six participants [18 chronically trained (CT: 14 males, 4 females) and 18 untrained (UT: 10 males, 8 females)] participated in this study. Two trials of twenty transient arterial occlusions were performed for NIRS-derived muscle oxidative capacity assessment. Muscle oxygen consumption ($$\dot{V}$$ V ˙ O2m) was estimated from deoxygenated hemoglobin (HHb), corrected for blood volume changes following Ryan (HHbR) and Beever (HHbB) equations, and from oxygen saturation (StO2) in VL and TA. Results Superimposing or averaging $$\dot{V}$$ V ˙ O2m or averaging the rate constants (k) from the two trials resulted in equivalent k values [two one-sided tests (TOST) procedure with 5% equivalence margin—P < 0.001]. Whereas HHbR (2.35 ± 0.61 min−1) and HHbB (2.34 ± 0.58 min−1) derived k were equivalent (P < 0.001), StO2 derived k (2.81 ± 0.92 min−1) was greater (P < 0.001) than both. k values were greater in CT vs UT in both muscles (VL: + 0.68 min−1, P = 0.002; TA: + 0.43 min−1, P = 0.01). Conclusion Different approaches for averaging trials lead to similar k. HHb and StO2 signals provided different k, although different blood volume corrections did not impact k. Group differences in k were detected in both muscles.