It is axiomatic that individuals with a greater peak O2 uptake (Vo2peak) sustain greater perfusive and diffusive O2 conductance across the active musculature in toto. However, it is unclear how these O2 conductances are regulated among knee extensor muscles that are spatially heterogeneous in blood flow, fiber type, and motor unit recruitment, in individuals whom vary in Vo2peak. PURPOSE: Using quantitative near infrared spectroscopy (NIRS) from rest to maximal exercise, we tested the hypotheses that with greater Vo2peak the vastus lateralis (VL) and rectus femoris (RF) muscles would evince: 1) a greater increase in deoxyhemoglobin concentration ([HHb], an index of O2 extraction) and [hemoglobin] ([tHb], an index of diffusive O2 potential); and 2) a right-shift in the [HHb] half-time (f50, an index of relative perfusion); together suggesting that a greater aerobic capacity is associated with improvements in both perfusive and diffusive O2 transport. METHODS: 22 healthy subjects completed ramp incremental cycling exercise (20 W·min-1) to the limit of tolerance. Pulmonary Vo2 was measured breath-by-breath. [HHb] and [tHb] were quantified in the VL and RF by time-resolved NIRS. Each NIRS profile was modeled with a sigmoid (y = B + A / [1 + exp-(-c+dx)], B is baseline, A is amplitude, c is a constant dependent on d, d is the slope of the sigmoid, and f50 = c/d). RESULTS: Vo2peak ranged from 37.7 to 66.4 ml·kg-1·min-1. Vo2peak was associated with the exercise-induced increase in [HHb] for both muscles (VL, r = 0.432; RF, r = 0.529; P < 0.05), and exercise-related increase in [tHb] for RF (r = 0.473, P < 0.05). However, Vo2peak did not correlate with f50 for [HHb]. CONCLUSIONS: As expected, greater Vo2peak during cycling was achieved, in part, via an increased capacity for O2 extraction in the knee extensors reflected in the greater amplitude for [HHb]. However, a greater capacity for diffusive O2 conductance (increase in [tHb]) to support increased O2 exchange, only related to Vo2peak in the RF muscle. These results support that a greater Vo2peak requires an increase in the maximal capacity for O2 conductance across the active musculature, while a regional change in the kinetics of O2 conductance at a given submaximal relative work rate is not an obligatory adaptation. Supported by JSPS-15K16476, 24247046, 26560362