Key Takeaway
Zone 2 training optimizes lactate clearance capacity by training mitochondria to use lactate as fuel, improving metabolic flexibility.
Summary
This landmark paper by Iñigo San-Millán and George Brooks explores the role of lactate in metabolism and how Zone 2 training specifically targets lactate clearance capacity.
The key insight is that lactate is not a waste product but a crucial metabolic fuel. Zone 2 training, performed at the intensity where lactate production equals clearance (~2 mmol/L), maximally stimulates mitochondrial adaptations that improve the body's ability to use lactate as fuel.
This explains why elite endurance athletes spend 80% of training time in Zone 2 - it builds the metabolic machinery that supports higher-intensity efforts.
Methods
- Review of lactate metabolism research
- Analysis of training zone physiology
- Integration of mitochondrial biogenesis mechanisms
Key Results
- Lactate is a primary fuel source, not waste
- Zone 2 intensity optimizes lactate shuttle training
- Mitochondrial density increases with Zone 2 training
- Improved fat oxidation occurs at Zone 2 intensity
Limitations
- Primarily a review/perspective paper
- Optimal Zone 2 protocols still being refined
- Individual variation in lactate thresholds