In this episode of The Athletes Compass, Dr. Paul Laursen and the team break down the science and practical application of the second threshold — also known as LT2, VT2, FTP, or critical power. They explain what physiologically happens when you cross this boundary, why base training is essential before adding threshold work, and how over-unders, tempo sessions, and VO2 max intervals raise performance. The conversation explores common mistakes athletes make (especially doing too much intensity), the role of durability, and how to assess threshold progress without lab testing. If you want to train smarter, improve pacing, and sustainably increase performance, this episode delivers a masterclass in intensity control.

1. LT1 vs LT2: LT1 (aerobic threshold) = top of Zone 2, sustainable “all-day” effort. LT2 (second threshold) = highest sustainable steady-state effort before rapid fatigue.
2. Above LT2: Glycolytic demand increases, lactate accumulates faster, heart rate drifts, and fatigue accelerates.
3. Functional vs Lab Testing: FTP and critical power are practical field markers of LT2. Lab tests measure physiology, but field tests often matter more for performance.
4. Day-to-Day Variation Is Real: Sleep, fueling, equipment, environment, and training phase can significantly affect test results.
5. Base Training First: A strong aerobic base (mitochondrial development) improves tolerance to threshold work and increases fat oxidation capacity.
6. Over-Unders Work Because: They stimulate mitochondrial adaptations by forcing lactate clearance and improving aerobic durability.
7. Intensity Control Matters: Spending more time in the correct zone is more beneficial than constantly pushing the top end.
8. Most Common Mistake: Too much high-intensity work without sufficient aerobic base.
9. Durability Is the Goal: Threshold training should build resilience so performance doesn’t break down late in races.

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