Figure 4. The effect of superimposing reactive hyperemia on the recovery from plantar flexion exercise on the relationship between microvascular partial pressure of O2 (PO2) and initial post exercise PCr resynthesis rate, an index of O2 utilization, in the context of diffusive and convective O2 transport. Muscle O2 utilization was inferred from the initial post exercise PCr resynthesis rate as this process is derived almost exclusively from oxidative phosphorylation . Microvascular PO2 was derived from the tissue oxygen index , assuming that the near infrared spectroscopy signal mainly originates from hemoglobin , and then computed from the O2-hemoglobin dissociation curve . Oxygen consumption, VO2; blood flow, Q; arterial oxygen content, CaO2; venous oxygen content, CvO2; diffusional conductance, DO2; Mean Capillary PO2, PCapO2.