What the MAF method is
MAF stands for Maximum Aerobic Function. The term was created by American practitioner Phil Maffetone, who developed the method through the 1980s observing that many endurance athletes lived sick, injured or stagnant from training too hard most of the time.
The central proposal is simple and somewhat counterintuitive: spend most of training running slowly, within a heart rate (HR) range low enough for aerobic metabolism to dominate. The promise is that, over time, you get faster at the same effort, burning fat more efficiently and without accumulating the stress that leads to injury and overtraining.
The 180 minus age formula
The heart of the method is the 180 formula. You calculate your aerobic HR ceiling like this: take 180, subtract your age and adjust according to your history.
MAF 180 formula: 180 minus age, with adjustments: +5 for those with two or more years of consistent training and documented progress; minus 5 for those injured, with an irregular history or no evolution; minus 10 for those recovering from serious illness, using continuous medication or in chronic overtraining.
Maffetone, 180 formulaA 40-year-old runner with consistent training would have a ceiling of 140 beats per minute. All base training is done at that HR or below it. No finishing the easy run breathless. If the heart rate climbs, you slow down, or even walk, to stay under the limit.
The MAF test and the Mark Allen case
The method uses a tracking test: run a fixed distance (for example, a few kilometers on a track) always at the MAF HR and note the pace. If over the months the pace at the same heart rate improves, your aerobic base is growing. If it worsens, something is wrong with recovery, stress or stimulus.
The most cited case is Mark Allen, six-time Ironman world champion. When he started working with Maffetone, he discovered that at the target HR of 155 bpm he could not run faster than about 8:15 per mile. A year training only at aerobic intensity and, at the same heart rate, his pace dropped to about 5:20 per mile.
Mark Allen and Maffetone accountIt is a powerful story. It is worth remembering that it is an individual account, from one of the greatest triathletes in history, not a controlled study. Even so, it illustrates the principle well: improving pace without raising physiological effort.
What the evidence says about low intensity training
Here is the method's strong part. The scientific basis that most of the volume should be light is solid and comes from outside the Maffetone universe. Physiologist Stephen Seiler, in the early 2000s, analyzed how elite athletes across endurance sports actually train and found a repeated pattern.
Elite endurance athletes do about 80% of volume at low intensity (below the first threshold) and about 20% at moderate to high intensity. That is the so-called polarized distribution, or the 80/20 rule.
Seiler, early 2000sMore recent systematic reviews reinforce that the polarized model tends to improve variables like peak VO2, though the effect size is modest and clearer in already well-trained athletes. In other words: the philosophy of running a lot and slowly has backing. Where the studies converge is on light volume as the base, not necessarily on the 180 formula as the right way to define that "slowly".
Where the 180 formula meets its limits
MAF's weak point is not the idea of training light, it is the single yardstick based only on age. Two people of the same age can have very different physiologies.
- The formula ignores real maximum HR and individual lactate thresholds. For some, 180 minus age falls well below the first threshold and becomes a truly easy effort. For others, the same number is already near or above the second threshold, and then it is no longer aerobic base training.
- It is poorly individualized at the extremes: the proponents themselves recognize that athletes over 65 may need additional adjustment.
- The method's authors, in a review published in a scientific journal, admit that the theoretical relationships between the MAF HR and maximal fat burning still need to be scientifically verified.
In the review by Maffetone and Laursen (2020), the authors themselves write that the MAF approach is useful for practitioners, but does not replace laboratory testing and that its physiological relationships need scientific validation.
Maffetone and Laursen, 2020, Frontiers in PhysiologyPros, cons and who it makes sense for
In favor: the method is simple, cheap (just an HR monitor), reduces the risk of training hard every day and teaches the beginner to hold the pace, which is precisely the most common mistake of those starting out. The underlying principle, lots of light volume, is aligned with the best evidence.
Against: the formula can underestimate or overestimate your real ceiling. Always running below a limit can be frustrating at first, when you need to walk to keep the HR from spiking, and an aerobic-only plan, with no intense stimulus, can leave performance on the table for more advanced athletes who benefit from that hard 20%.
MAF is a training organization tool, not a diagnosis. The 180 formula is a useful starting point, but if you have a health condition, use medication or want precision, evidence indicates that a threshold test with an exercise physiology professional gives a far more reliable range than mental math.
