Empirical Cycling Podcast Watts Doc #20: The Fick Equation Part 1 - A VO2 Difference
Jun 2, 2020
A deep dive into the Fick equation focused on how muscles extract oxygen. They explore oxygen diffusion mechanics, roles of hemoglobin and myoglobin, and how capillary geometry and density shape uptake. Studies on one‑leg training and angiogenesis are discussed, plus why whole‑body VO2max is often limited by cardiac output rather than diffusion alone.
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Fick Equation Shows Delivery Dominates Utilization
- VO2max is the product of cardiac output and arterial-venous O2 difference, so utilization alone can't increase uptake without delivery.
- Cole A. Moore explains VO2max = stroke volume × heart rate × AVO2 difference and why the terms aren't equally limiting.
How AVO2 Difference Is Measured And Reported
- AVO2 difference measures how much oxygen is removed from arterial blood as it passes tissues, often reported as milliliters O2 per 100 ml blood.
- Cole A. Moore notes common reporting formats like volume percentage and mixed venous (V̄) values from femoral or brachial samples.
Globins Boost Solubility But Do Not Actively Transport O2
- Myoglobin and hemoglobin reversibly bind O2 via a heme group with iron, increasing O2 solubility but not actively moving it.
- Cole A. Moore explains myoglobin's high affinity and heme structure that permits reversible O2 binding.