The Physiology of Endurance Running Podcast Physiological failure guaranteed... the severe intensity domain
14 snips
Jan 28, 2026 They unpack the severe intensity domain where physiological responses become unstable and cannot hold steady. Conversation covers rising VO2, heart-rate drift and fast-twitch recruitment during high-intensity work. They compare heavy and severe efforts, talk practical pacing and session design for VO2 work. They also discuss recovery limits, how often to do hard days, and why elites space intense sessions.
AI Snips
Chapters
Transcript
Episode notes
Instability Above The Second Threshold
- Above LT2 physiological variables don't reach a steady state and drift rapidly toward VO2max.
- That drift forces increasing anaerobic recruitment and rising metabolic stress until failure occurs.
What Actually Causes Fatigue Here
- Severe work produces continuous rises in oxygen uptake, heart rate and muscle metabolites across a session.
- Those dynamic changes, not glycogen depletion, are the primary fatigue drivers in this domain.
High Intensity Triggers AMPK And PGC‑1α
- ADP/AMP accumulation activates AMPK, which upregulates PGC-1α and mitochondrial biogenesis.
- Higher intensity thus stimulates mitochondria and other adaptations via distinct signaling from lower intensities.