Compound or practice · Training

Zone 2 training

The unglamorous aerobic base that moves resting HR, mitochondria, and long-term health risk more than anything else per hour.

Overall grade: Grade A
Last revised: Jun 22, 2026; 4
graded outcomes: 3
references listed

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A hand-written entry in Prometheus's bundled library. Its grades are the entry's own reading of the evidence, not a peer-reviewed review.

5 at grade A · 3 at grade B — 8 graded rows

What is known

Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.

Outcome	Grade	Effect size	Agreement
Resting heart rate3–6 bpm over 8–16 weeks at 3–4h/week	Evidence grade A	Moderate	high
VO₂max (untrained→trained)Base volume sets the floor; intervals set the ceiling	Evidence grade A	Large	high
Fat oxidation capacityDirectly trained at this intensity	Evidence grade A	Moderate	high
All-cause mortality (cohort)Observational but dose-responsive and robust	Evidence grade B	Large	high

Resting heart rateEvidence grade A
3–6 bpm over 8–16 weeks at 3–4h/week
Moderatehigh
VO₂max (untrained→trained)Evidence grade A
Base volume sets the floor; intervals set the ceiling
Largehigh
Fat oxidation capacityEvidence grade A
Directly trained at this intensity
Moderatehigh
All-cause mortality (cohort)Evidence grade B
Observational but dose-responsive and robust
Largehigh

Conditions

How the entry reads its effect on diagnosed conditions: the direction first, then the grade. Never a substitute for the person who treats you.

Hypertension ImprovesEvidence grade A5–8 mmHg systolic — first-line lifestyle therapyGrade A
Type 2 diabetes ImprovesEvidence grade AInsulin sensitivity scales with weekly aerobic volumeGrade A
Depression ImprovesEvidence grade BEffect sizes rival first-line treatment in mild-moderate casesGrade B
Knee osteoarthritis May improveEvidence grade BLow-impact modalities; pain drops with graded volumeGrade B

Weekly minutes vs mortality-risk reduction · dose–response

Up: risk reduction %. Across: min/week. The curve keeps bending past the guidelines — 150 min captures most of it, 300 is the sweet spot.

Resting HR on 3–4h/week of base · time course

Up: bpm vs start. Across: weeks. Slow and compounding — this is the metric your Cardio agent forecasts from.

The evidence in words

What it is

Steady work at the top of your purely-aerobic range — conversational pace, nose-breathing possible, roughly 60–70% of max HR. The physiological target is maximal fat oxidation and mitochondrial signaling without meaningful lactate accumulation.

What the evidence shows

Aerobic base volume is the single strongest trainable predictor of resting HR decline and VO₂max floor. 150–300 min/week of moderate cardio maps to the largest all-cause-mortality risk reductions in cohort data, and interval work stacks on top of a base — it doesn't replace it. Chest-strap HR is worth using: wrist optics drift exactly in this intensity band.

What to expect

Weeks 1–4: pace at a fixed HR improves noticeably. Months 2–4: resting HR down 3–6 bpm, HRV trend up. It should feel almost too easy — if you need music to survive it, you're in zone 3.

How it is used

As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.

Minimum effective: 2 × 45 min/week keeps the base; 3–4 × 45–60 min builds it.
Intensity check: Talk test: full sentences comfortably. HR: ~180 minus age as a crude ceiling, or 65–70% of true max.

Goes with

Caffeine + L-Theanine3–6 mg/kg caffeine pre-session is the best-evidenced ergogenic there isEvidence grade B
Omega-3 (EPA/DHA)The cardio-risk stack: base volume + lipid controlEvidence grade A

Questions people ask

Can I just do HIIT?

Intervals raise VO₂max fast but plateau without base volume underneath — and the injury/recovery cost per adaptation is worse. Do both; weight the base.

Incline walking count?

Fully, if HR lands in the band. Modality is irrelevant; time-in-zone is the currency.

Entries that share this one's tags or conditions.

Sleep architectureThe recovery system everything else compounds on — deep and REM timing matter more than raw hours.Evidence grade A
Beetroot / Dietary NitrateDietary nitrate lowers the oxygen cost of exercise — a legit endurance aid, best in recreational athletes.Evidence grade B
Beetroot / Dietary Nitrate for Blood pressureEvidence grade B — Modest reductionEvidence grade B
Beetroot / Dietary Nitrate for Endurance / O2 costEvidence grade B — Larger in recreational athletesEvidence grade B

Sources

As this entry records them: title, journal and year. None carries a DOI or PubMed id, so none is linked as a verified paper. Each link searches PubMed for the title; check that what you find is what the entry describes.

1.Physical activity and all-cause mortality: dose-response meta-analysis — BMJ, 2019. Search PubMed (opens in a new tab)
2.Training-intensity distribution in endurance athletes — Sports Med, 2015. Search PubMed (opens in a new tab)
3.Maximal fat oxidation intensity in trained and untrained adults — Int J Sports Med, 2003. Search PubMed (opens in a new tab)

Last revised Jun 22, 2026. A grade is this entry's reading of the evidence, not medical advice.