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Is zone 2 cardio the key to longevity?

What you hear: “Steady, easy 'zone 2' cardio is the key to living longer.”

What the studies found

Fitter people live longer: across 33 studies of 102,980 adults, each step up in fitness (about 1 km/h faster running speed) went with a 13% lower death rate. US adults meeting the aerobic activity guideline had a 29% lower death rate. Both are links from watching people; trials of exercise in about 50,000 older or ill people have not shown fewer deaths. On intensity, interval training raised fitness slightly more than steady endurance training (about 1.2 mL/kg/min more), and a 5-year trial of 1,567 older Norwegians found a non-significant trend to fewer deaths with intervals than with moderate steady exercise.

What you could do

Aim for regular aerobic exercise you enjoy at any intensity, ideally including some harder efforts, rather than worrying about staying in one heart-rate zone.

See it in the habit library, with what it means for your own longevity score.

Not medical advice. General information from published studies, not a diagnosis or a treatment plan. Talk with your doctor before starting a supplement or changing a medicine, especially if you are pregnant, take other medicines or have a health condition.

How we judged it

Partly true: Some truth, but oversold as usually said. We judge the claim as it is usually said online, not the habit itself. Trials assign people at random, so they can show cause; observed studies follow people and show a link, not proof. Last checked: October 2026.

The studies, in their own words

1. Kodama et al. JAMA 2009

   Pooled RRs of all-cause mortality and CHD/CVD events per 1-MET higher level of MAC (corresponding to 1-km/h higher running/jogging speed) were 0.87 (95% confidence interval [CI], 0.84-0.90) and 0.85 (95% CI, 0.82-0.88), respectively.

2. Zhao et al. BMJ 2020

   aerobic activity (n=113 851; 0.71, 0.69 to 0.72) were found to be at reduced risk of all cause mortality

3. Ballin et al. J Intern Med 2021

   the current evidence shows that exercise does not prevent premature mortality or CVD, with inconsistent evidence for fractures.

4. Milanovic et al. Sports Med 2015

   When compared with endurance training, there was a possibly small beneficial effect for HIT (1.2 mL·kg(-1)·min(-1); ±0.9 mL·kg(-1)·min(-1))

5. Stensvold et al. BMJ 2020

   When HIIT was compared with MICT as reference group an absolute risk reduction of 2.9 percentage points was observed (0.51, 0.25 to 1.02) for all cause mortality.

6. Storoschuk et al. Sports Med 2025

   We conclude that current evidence does not support Zone 2 training as the optimal intensity for improving mitochondrial or fatty acid oxidative capacity.

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