Before Zone 2 had a name, there was 180 minus age.
Decades before podcasts discovered easy aerobic training, coach Phil Maffetone was capping athletes’ heart rates with one number. The MAF 180 formula is still everywhere in endurance circles — here’s how it works and where it fits.
One cap, four adjustments.
Everything here is from Maffetone’s own write-up of the formula — including the modifiers most people skip.
Edge cases, per the same page: athletes over 65 may add up to 10 beats — but only if they qualify for the +5 group — and the formula doesn’t apply at 16 and under, where a flat 165 has been used instead.
The proof of concept won six Ironmans.
Mark Allen — six-time Hawaii Ironman champion — credits the approach directly: “Using Phil’s training program… I have been able to rack up a long list of international triathlon victories, including six Hawaiian Ironman titles.” In a later interview he described the payoff of years of patient aerobic work: running 5:30–5:45 per mile at just 155 bpm.
How MAF maps onto zones.
Run the numbers for a 40-year-old with no adjustments: MAF gives a 140 bpm ceiling, while an estimated max of 180 puts consumer-model Zone 2 (60–70%) at 108–126 bpm. MAF’s cap sits above that band — closer to the threshold-anchored “zone 2” used in sports science (roughly 72–82% of max). Different rulers, same idea: spend your base miles below the point where easy stops being easy.
If you train MAF-style with Zone2, the mapping is one step: set your Zone 2 upper limit to your MAF number in the Health app, and your watch enforces the cap in real time.
Set the cap. Keep the cap.
Zone2 is free. Point it at your MAF ceiling or your zones, and your watch taps you the moment a workout crosses the line.