intensity — the sweet spot for and .
Studying elite cyclists and metabolic patients, San-Millán and Brooks showed — roughly 60–70% of maximum heart rate, or just below the first — is where fat oxidation peaks and where is most strongly stimulated per hour.
What the researchers did
The team measured blood lactate and substrate use across intensities in both elite endurance athletes and metabolically-impaired patients, mapping the intensity where fat oxidation was highest.
The key finding
At 60–70% HRmax, lactate stays around 2 mmol/L and fat oxidation peaks. This is the intensity that maximises gains — the underpinning both and health span.
Why it matters
is where you build the engine. It should feel conversational — you can hold a full sentence but not sing. Ninety minutes at Zone 2 does more for your mitochondria than 20 minutes of moderate-hard .
Get 2–4 hours a week at 60–70% HRmax (conversational pace). Nose-breathing is a decent proxy.
- 1.6–2.2Daily protein intake that maximises hypertrophy.
- 7–9Nightly sleep for recovery, hormones and growth hormone release.
- 8,000Daily step count where all-cause mortality risk levels off — largely a NEAT effect.
- 3–5Creatine monohydrate dose — no loading needed.
- 3–6Pre-training caffeine dose that reliably improves strength and endurance output.
- 25–38Daily fibre intake linked to lower all-cause mortality and a healthier gut microbiome.