Using Exercise Stress Tests to Reveal Dysfunction

In this episode I am joined by Dr Iñigo San Millán, exercise physiologist, researcher, and coach to Tour de France champion Tadej Pogačar. His work places lactate at the centre of human health, showing it as a fuel and biomarker rather than a waste product.

We discuss how lactate offers a new lens on mitochondrial health, what Zone 2 training really achieves, and why these insights apply to both elite athletes and anyone seeking longevity.

What We Cover

• Lactate myths and the truth about its role in energy
• Differences between athletic and diseased lactate profiles
• Zone 2 training and mitochondrial health
• Balancing training methods for metabolic flexibility
• Diet, lactate, and critiques of Zone 2

This conversation shows why understanding lactate could be key to improving performance, preventing disease, and ageing well.

You can connect with Dr Iñigo San Millán on Instagram and Twitter, where he shares insights on exercise physiology, metabolism, and performance. Follow along to learn more about his research and practical applications for both athletes and everyday health.

• Understanding Lactate as a Biomarker and Signalling Molecule (00:00)
• Historical Misconceptions About Lactate and Fatigue (04:03)
• How the Body Uses Lactate as a Fuel Source (06:09)
• Lactate in Health, Metabolic Function, and Disease (10:25)
• Exercise, Lactate Dynamics, and Energy Balance (16:39)
• What Research Reveals About Lactate and Mitochondrial Function (19:03)
• Exercise Prescription and Training Zones Explained (26:20)
• High-Intensity Exercise: What Happens to Lactate Levels? (37:87)
• VO₂ Max, Mitochondria, and Aerobic Fitness (45:02)
• Supporting Mitochondrial Function for Disease Prevention (48:37)
• Designing Exercise Programmes for Longevity and Healthspan (51:19)
• Resistance Training and Its Impact on Metabolic Health (1:00:10)
• How Diet and Exercise Influence Mitochondrial Function (01:04:42)
• Is Zone Two Training Really the Key to Endurance? (01:10:39)
• Final Reflections on Lactate, Training, and Metabolic Adaptation (01:19:47)

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Simon Hill, MSc, BSc (Hons)

• Creator of theproof.com
• Host of The Proof with Simon Hill
• Author of The Proof is in the Plants

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