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Dr. Jack Daniels explains why Easy (E) running is foundational for all runners. A massive aerobic base is a

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what it claims

Building the large majority of your running volume at an easy pace ("E pace," below the aerobic threshold) before adding harder sessions is a solid, widely-shared coaching principle — even though the exact "ideal" percentage of easy running isn't scientifically fixed.

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Stripped of Jack Daniels' name and authority, the claim amounts to a classic endurance-training principle: an aerobic base built at easy intensity (65-79% of max heart rate per…

noli's read

Stripped of Jack Daniels' name and authority, the claim amounts to a classic endurance-training principle: an aerobic base built at easy intensity (65-79% of max heart rate per Daniels' formula) precedes and supports harder quality sessions. This is consistent with the polarized training model, where even elite athletes spend roughly 80% of their volume at low intensity. The mechanisms invoked (mitochondrial density, capillarization, cardiac strength) are plausible and documented in exercise physiology, but the Storoschuk et al. (2025) review notes that evidence for this zone's specific superiority over other approaches at matched volume remains limited and mixed. The practical advice — don't skip the aerobic base before jumping into hard sessions — is solid and widely agreed upon among coaches, but presenting one precise percentage of easy training as a fixed scientific rule would go beyond what the literature supports.

the sources

Claimed by V.O2. Noli grades the claim, never the person.

Decoded by Noli · August 3, 2026 · the original post

What the graded evidence says

Evidence: C

Effect: endurance performance (VO2max, time trial) polarized vs threshold intensity distribution — polarized modestly favored in a small meta-analysis (only 3-4 RCTs); a larger 2024 review found no clear superiority over other distributions
Measured on: trained endurance athletes (>2 years experience); mechanistic mitochondrial data in adults

The head-to-head evidence for a specific intensity split is limited to a handful of small trials with mixed results, so precise prescriptions like exact Zone 2 percentages shouldn't be treated as settled science.

V.O2 in the Register1 claims gradedSee their record →

Noli has read similar claims

Other advice in the Register that leans on the same research.

Deliberately running slow (zone 2, conversational effort) builds long-term aerobic base — but framing it as THE method that "grows your heart" and beats every other approach goes further than the evidence supports.

mixedThe Running Week

Aiming for 180-200 minutes a week of zone 2 cardio (an effort where you can still hold a conversation) matches the protocols Peter Attia has published, and that intensity genuinely leaves room to work or listen to a podcast at the same time.

holds upAndrew Huberman, Ph.D.

"Zone 2" does burn a higher percentage of fat during the effort itself, but overall fat loss depends on total calories burned across the day, not the intensity zone — and walking and running burn very similar calories over the same distance. It's not a shortcut to weight loss.

holds upJeremy Ethier, BKin

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