Evaluating the NIRS-derived microvascular O(2) extraction “reserve” in groups varying in sex and training status using leg blood flow occlusions

It has been demonstrated that the plateau in the near-infrared spectroscopy (NIRS) derived deoxygenated hemoglobin and myoglobin (deoxy[Hb+Mb]) signal (i.e., deoxy[Hb+Mb](PLATEAU)) towards the end of a ramp-incremental (RI) test does not represent the upper-limit in O(2) extraction of the vastus lateralis (VL) muscle, given that an O(2) extraction reserve has been recently observed. This study aimed to investigate whether this O(2) extraction reserve was present in various populations and whether it exhibited sex- and/or training- related differences.Sixteen men- 8 untrained (27±5 years; 83±11 kg; 179±9 cm), 8 trained (27±4 years; 82±10 kg; 182±8 cm) and 9 trained women (27±2 years; 66±10 kg; 172±6 cm) performed a RI cycling test to exhaustion. The NIRS-derived deoxy[Hb+Mb] signal was measured continuously on the VL as a proxy for O(2) extraction. A leg blood flow occlusion (i.e., ischemia) was performed at rest (LBF(OCC) 1) and immediately post the RI test (LBF(OCC) 2).No significant difference was found between the deoxy[Hb+Mb] amplitude during LBF(OCC) 1 and the deoxy[Hb+Mb](PLATEAU) (p>0.05) nor between baseline (bsln) deoxy[Hb+Mb] values. deoxy[Hb+Mb] amplitude during LBF(OCC) 2 was significantly greater than LBF(OCC) 1 and at deoxy[Hb+Mb](PLATEAU) (p<0.05) with group means ~30–45% higher than the deoxy[Hb+Mb](PLATEAU) and LBF(OCC) 1 (p<0.05). No significant differences were found between groups in O(2) extraction reserve, regardless of sex- or training-statusThe results of this study demonstrated the existence of an O(2) extraction reserve in different populations, and that neither sex- nor training-related differences affect the amplitude of the reserve.