Elite Endurance Athletes Consume 120g Carbs Per Hour During Races. New Research Says You Only Need 10g (Here’s Why)

Heart rate training has become one of the most debated topics in endurance sports.

Yet few approaches have stood the test of time quite like Dr. Phil Maffetone’s MAF method.

Developed in the late 1970s, the MAF 180 formula remains as relevant today as it was over four decades ago, helping runners build aerobic fitness while staying healthy and injury-free.

In a recent episode of the Endurance Lab podcast, Dr. Maffetone shared the origins of his formula, how it aligns with modern concepts like zone 2 and aerobic threshold, and why so many athletes still misapply it.

The Birth of the MAF Formula

Dr. Maffetone began his practice in 1977 in a New York City suburb, right in the middle of the running boom. He quickly noticed a troubling pattern: runners were sacrificing their health for fitness.

I was into healthcare. I wanted to help people get healthy. And here come all these competitive runners early on, willing to sacrifice their health, willing to get injured and sick. And unfortunately, some of them die to get better, to get faster. And that was not acceptable for me.

He began working with injured runners, watching them train, and using primitive heart rate monitors available at the time. What he discovered changed everything: runners performed better with improved gait mechanics when their heart rates were lower than where they typically trained.

For years, he worked clinically with individual athletes, manually determining the right training heart rate for each person. Then one day during a lecture, someone asked how others could replicate his approach.

I was a little embarrassed because I didn’t have an answer. And I went home and I thought there must be a formula because this is human endeavor. This is activity. This is a logical thing. I’m not doing anything mystical or magical.

The result was the MAF 180 formula: 180 minus your age, adjusted by one of four modification categories based on training history and health status.

What the MAF Formula Actually Measures

At the time Dr. Maffetone created the formula, he didn’t have access to lactate testing or gas exchange analysis. He relied on clinical observation, gait analysis, and basic heart rate data.

Only later did laboratory testing confirm what he had discovered intuitively: the MAF heart rate corresponds with aerobic threshold, the point where fat oxidation is maximized and lactate begins to accumulate.

The laboratory evaluations started coming in and people started sending me stuff from their labs about how the measures we found using your formula correspond to maximum fat burning and lactate aerobic threshold.

This aligns closely with what many today call zone 2 training or the first lactate threshold, where blood lactate remains at or below 2 millimoles per liter.

How Most Athletes Misapply the Formula

Despite its simplicity, runners frequently misapply the MAF formula. The most common mistake? Adding extra beats because the prescribed heart rate feels “too slow.”

You put on a heart monitor, you go out, and during your workout, you’re thinking, ‘This can’t be right. This is so slow. I have to walk the hills.’ No. What you found is your aerobic system is at that level. That’s how bad you are aerobically speaking.

Dr. Maffetone explains that this discomfort reveals the true state of your aerobic fitness. If your MAF heart rate forces you to walk uphills, that’s your current aerobic baseline.

The solution isn’t to cheat by raising the heart rate. It’s to stay patient and let your aerobic system develop.

You want to bring your aerobic system up higher, develop it really well. You’ll burn off the excess body fat. And because you’re burning more fat for energy, you’ll have more energy for running. Therefore, you could run faster at the same aerobic heart rate.

When in Doubt, Go Lower

One of Dr. Maffetone’s most practical pieces of advice: if you’re uncertain about your MAF heart rate, choose the lower number.

When in doubt, choose a lower heart rate because you can’t go wrong by doing that. So it takes you an extra month to break a PR in your runs. You’re going to be a lot healthier for it and you’re going to break more PRs in the future.

This conservative approach ensures you’re truly building aerobic capacity without dipping into higher intensities that can impair recovery and long-term progress.

The MAF Test: Your Progress Tracker

The MAF test is simple: run a set distance (like a 5K or specific route) at your MAF heart rate and track your pace over time. If you’re getting faster at the same heart rate, your aerobic system is improving.

If your pace plateaus or slows, something is wrong—often the heart rate is too high, recovery is insufficient, or diet is interfering with fat metabolism.

If the MAF test is still improving, if your MAF test is constantly improving, then whatever you’re doing is working.

Adjusting for Heat, Illness, and Life Stress

Environmental factors like heat, humidity, and low barometric pressure can significantly affect heart rate. Dr. Maffetone recommends keeping the same MAF heart rate even in challenging conditions, which may mean slowing down considerably.

For athletes who get sick more than twice a year, he suggests subtracting five beats from the MAF heart rate, even if training is progressing well.

If you are getting sick, which means your immune system is down here instead of up here. It’s not that your son is bringing germs home. It’s that your immune system cannot fight those germs.

Building an Aerobic Base Before Adding Speed

Dr. Maffetone advocates for a dedicated aerobic base-building phase lasting three to six months, depending on the athlete’s starting point. During this period, all training stays at or below the MAF heart rate—no speed work, no racing.

The goal is to develop the aerobic system fully before introducing anaerobic training.

The way you know you’ve built enough aerobic power is that your MAF test, you’ll keep getting faster and faster, and at some point you’ll hit a plateau. That’s kind of an ideal place to add speed work or add any anaerobic training or add racing.

He’s conducted studies where seasoned runners trained aerobically for months, then jumped straight into a race. 76% of them ran a personal best—without any formal speed work.

The 80/20 Rule and Aerobic Training

While Dr. Maffetone agrees that an 80/20 split between low and high intensity can work, he emphasizes it shouldn’t apply year-round.

Athletes first need to establish a strong aerobic base. Only after that foundation is built should they introduce higher-intensity work at a ratio that makes sense for their goals and recovery capacity.

Diet, Fat Burning, and the Two-Week Test

Aerobic training and fat metabolism are inseparable. Dr. Maffetone stresses that you cannot build a strong aerobic system on a diet high in refined carbohydrates and sugar.

You cannot have a good aerobic system if you’re eating junk food and you’re eating sugar. Period.

He developed the Two-Week Test, a short-term dietary reset that eliminates all refined carbohydrates and reduces high-glycemic natural carbs like fruit and juice. The goal is to shift the body into better fat-burning mode and observe changes in energy, performance, and body composition.

Some athletes see dramatic improvements in their MAF test pace—sometimes a full minute per mile faster—after just two weeks of dietary adjustment.

Rethinking Race-Day Nutrition

Conventional wisdom suggests endurance athletes need 100+ grams of carbohydrate per hour during races. Dr. Maffetone disagrees.

When the aerobic system is well-developed, the body efficiently burns fat for energy, drastically reducing the need for exogenous carbohydrates.

The average lean athlete has enough fat energy-wise to take them hundreds of miles. What a great deal that is. Hey, let’s tap into that energy during our race.

He references emerging research suggesting athletes may only need 10 grams of carbohydrate per hour—a stark contrast to mainstream recommendations. Consuming less also reduces gastrointestinal distress, a common race-day issue.

Measuring Body Fat the Simple Way

Dr. Maffetone advocates a simple method for assessing body composition: waist circumference should be less than half your height.

Measure at the level of your belly button, without sucking in. If your waist exceeds this threshold, you’re likely over-fat and insulin resistant—even if you’re a regular runner.

Your waist should be less than half your height. And if you’re not, you’re over-fat. Period. End of discussion. Very, very accurate.

Fasted Training: Not Recommended

Despite the popularity of fasted cardio, Dr. Maffetone advises against it.

As soon as you wake up, your blood sugar will gradually get more unstable. And if your blood sugar in the middle of a run starts to crash, that’s a bad thing. It’s also a bad way to train your body.

He recommends consuming something light before training—such as his “fat-burning coffee” recipe, which includes protein, fat, and caffeine—to stabilize blood sugar and support performance.

Strides and Downhill Running During Base Training

If athletes want to include faster running during base training, Dr. Maffetone suggests short 7-second strides or, even better, running downhill at MAF heart rate.

Downhill running allows for faster turnover without exceeding aerobic thresholds, providing a natural speed stimulus while staying within the aerobic zone.

Final Takeaway: Keep It Simple and Have Fun

Above all, Dr. Maffetone emphasizes that training should be enjoyable.

This is supposed to be fun. You know, you look at these runners on the highway as I drive by and I’m thinking, ‘Oh my god, that person is not having fun.’ Don’t forget to have fun, please.

He encourages athletes to resist the “no pain, no gain” mentality and remember that endurance means being able to perform well—and enjoy it—for a long time.

With a healthy brain, strong aerobic system, and proper nutrition, athletes can continue improving well into their later years.

The MAF method isn’t flashy. It won’t make for impressive social media posts. But it works—and it’s been working for over 40 years.