Greater<i>V</i>O_2peakis correlated with greater skeletal muscle deoxygenation amplitude and hemoglobin concentration within individual muscles during ramp-incremental cycle exercise

Abstract

It is axiomatic that greater aerobic fitness (V˙O_2peak) derives from enhanced perfusive and diffusive O₂ conductances across active muscles. However, it remains unknown how these conductances might be reflected by regional differences in fractional O₂ extraction (i.e., deoxy [Hb+Mb] and tissue O₂ saturation [S_tO₂]) and diffusive O₂ potential (i.e., total[Hb+Mb]) among muscles spatially heterogeneous in blood flow, fiber type, and recruitment (vastus lateralis, VL; rectus femoris, RF). Using quantitative time-resolved near-infrared spectroscopy during ramp cycling in 24 young participants (V˙O_2peak range: ~37.4-66.4 mL kg^-1 min^-1), we tested the hypotheses that (1) deoxy[Hb+Mb] and total[Hb+Mb] at V˙O_2peak would be positively correlated with V˙O_2peak in both VL and RF muscles; (2) the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) during submaximal exercise would not differ among subjects differing in V˙O_2peak Peak deoxy [Hb+Mb] and S_tO₂ correlated with V˙O_2peak for both VL (r = 0.44 and -0.51) and RF (r = 0.49 and -0.49), whereas for total[Hb+Mb] this was true only for RF (r = 0.45). Baseline deoxy[Hb+Mb] and S_tO₂ correlated with V˙O_2peak only for RF (r = -0.50 and 0.54). In addition, the deoxy[Hb+Mb] slopes were not affected by aerobic fitness. In conclusion, while the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) did not differ between fitness groups the capacity to deoxygenate [Hb+Mb] (index of maximal fractional O₂ extraction) correlated significantly with V˙O_2peak in both RF and VL muscles. However, only in the RF did total[Hb+Mb] (index of diffusive O₂ potential) relate to fitness.