Working skeletal muscle under low-oxygen conditions runs glycolysis anaerobically, regenerating NAD⁺ via lactate dehydrogenase:
Glucose + 2 ADP + 2 Pi → 2 Lactate + 2 ATP
That lactate leaves the muscle, travels through the bloodstream, and enters the liver, where gluconeogenesis runs the pathway in reverse — rebuilding glucose, but at a much higher energetic price:
2 Lactate + 6 ATP-equivalents → Glucose + 6 ADP
The new glucose is released back into the blood and can return to the muscle, completing the Cori cycle. Hepatic uptake is modelled with Michaelis–Menten saturation:
clearance = Vmax · [Lactate] / (Km + [Lactate])
Vmax = capacity slider · rate constant, Km = 2 mM (fixed)
- Exercise intensity — sets how fast the muscle dumps lactate into the blood (anaerobic glycolytic flux).
- Liver capacity — the liver's Vmax for converting lactate back to glucose (fed/well-perfused liver vs. fasted/impaired).
- Blood flow — how fast lactate and glucose packets physically transit the vessel between organs.
- Net ATP balance — muscle nets +2 ATP per glucose-equivalent shuttled out as lactate, but the liver spends 6 ATP-equivalents rebuilding it, so the whole-body balance of the cycle itself is negative: the liver is effectively subsidising the muscle's ATP with energy from its own fat oxidation. This is the textbook "cost of the Cori cycle."
- The kinetics panel plots hepatic clearance rate against blood lactate directly from the same Michaelis–Menten equation driving the diagram — the dot marks where the model currently sits on that saturating curve, and where it crosses the flat production-rate line is the steady state the lactate level is converging toward.
Real-world relevance: this shuttle is why blood lactate rises during sprints and heavy lifting, why it clears over the following minutes at rest, and why liver disease or a fasted state can blunt that clearance and prolong post-exercise lactate elevation.