Greater [Formula: see text] O(2peak) is correlated with greater skeletal muscle deoxygenation amplitude and hemoglobin concentration within individual muscles during ramp‐incremental cycle exercise

It is axiomatic that greater aerobic fitness ([Formula: see text] O(2peak)) derives from enhanced perfusive and diffusive O(2) conductances across active muscles. However, it remains unknown how these conductances might be reflected by regional differences in fractional O(2) extraction (i.e., deoxy [Hb+Mb] and tissue O(2) saturation [S(t)O(2)]) and diffusive O(2) 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 ([Formula: see text] 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 [Formula: see text] O(2peak) would be positively correlated with [Formula: see text] 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 [Formula: see text] O(2peak). Peak deoxy [Hb+Mb] and S(t)O(2) correlated with [Formula: see text] 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(t)O(2) correlated with [Formula: see text] 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 O(2) extraction) correlated significantly with [Formula: see text] O(2peak) in both RF and VL muscles. However, only in the RF did total[Hb+Mb] (index of diffusive O(2) potential) relate to fitness.