The claimEvidence A · guideline-tier
Low-HR zone burns more fat
The evidence
Higher fat % at low intensity ≠ more fat burned in absolute terms; total expenditure + EPOC favor high intensity.
The mechanism, in brief
Zone 2 training = sustained aerobic exercise held below LT1 (about 60–70% of maxHR / 70% of VO2max / 'can still hold a full conversation'), typically 30–90 minutes per session.
Sources (3)
- Hawley, J. A., Lundby, C., Cotter, J. D., & Burke, L. M. (2018). Maximizing cellular adaptation to endurance exercise in skeletal muscle. Cell Metabolism, 27(5), 962-976. The physiological basis for low-to-moderate intensity (Zone 2) work as the dominant driver of mitochondrial biogenesis and fat-oxidation capacity.
- Coyle, E. F. (1995). Substrate utilization during exercise in active people. The American Journal of Clinical Nutrition, 61(4 Suppl), 968S-979S. Classic dataset on the fat/carbohydrate oxidation cross-over with intensity — the empirical basis for the Zone 2 'fat-burning' framing (and the limits of that framing).
- Brooks, G. A. (2018). The science and translation of lactate shuttle theory. Cell Metabolism, 27(4), 757-785. Definitive modern review establishing lactate as fuel rather than waste; the 'lactic acid burn' framing is anatomically and biochemically incorrect.