The Physiology of Endurance Running Podcast Between Two Thresholds: Everything you need to know about Zone 3
Jan 21, 2026
A deep dive into Zone 3, the heavy intensity domain between two physiological anchors. They unpack how lactate behaves and why heart rate and RPE help identify thresholds. Practical tips cover rep lengths, session pacing, and using races to estimate LT2. They also explore which adaptations Zone 3 best delivers and when higher intensity is needed.
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Dan’s 40k Day With Mixed Reps
- Dr Dan Osborn-Nash described a 40k day with mixed sessions including five-by-3k and mile reps off 90s rest.
- He felt the mixed metric sessions produced unexpectedly good paces and valued company for pushing efforts.
Anchor Thresholds With Data Or RPE
- Use lab tests (lactate or gas exchange) to anchor LT1 and LT2 when available.
- If no lab, use well-paced race heart-rate data and RPE to estimate thresholds and guide sessions.
Zone 3 Is An Intensity Range Not A Pace
- Zone 3 (heavy domain) sits between LT1 and LT2 and is defined by elevated but stable lactate.
- You can change speed and rep duration while keeping the same physiological stress in this domain.