For the past few months, I’ve been working in various capacities with Phil Maffetone, who has made many important contributions to exercise science and the endurance sports. He is a proponent that aerobic function—the ability of the aerobic system to utilize fat and oxygen to power the body—is the foundation for all health and athletic achievement.

In a recent article, I discussed this view from an evolutionary perspective: the aerobic system is in charge of the long-term upkeep of the body. Conversely, the functioning of the anaerobic system (which burns sugar in the absence of oxygen) is tied to the autonomic stress response, and necessarily coincides with a high heart rate. The organism primarily uses the anaerobic system to survive an imminent threat to its existence, or (in the case of predators) to capitalize on an opportunity for its survival.

When the anaerobic system stays on for too long—or becomes responsible for the body’s upkeep—chaos ensues. The Maffetone Method (also known as MAF) is all about bringing order to this chaos, and therefore facilitating the body to develop correctly.

A majority of people who try out Phil’s recommendations for the first time—(train at a heart rate that guarantees aerobic function while excluding all anaerobic function)—find that this means running very, very slow. And furthermore, a number of people don’t observe changes to their “aerobic fitness” for some time.

The problem isn’t that the method “doesn’t work.” It’s just that some of our bodies (and in particular, our aerobic engines) are in a state of utter disrepair—and the body is an extremely smart investor. The body will sometimes use the fledgling aerobic system to patch itself up and fill in the cracks before using its newfound potential for anything else.

I often hear that the aerobic system develops slowly. I believe that it develops astonishingly quickly. But while our attention is on the “fitness” we so desperately want—which we want so much that we rarely bother to define it—we miss the fact that the aerobic system is diligently working to achieve it.

Often, the body’s last priority is increasing athletic ability—as it should be. Think about it: if we are succumbing to infections because our aerobic system is struggling to power our immune response, or our bones have insufficient density due to increased acidity (which the aerobic system potently counteracts), then the last thing that we want is to be subjecting this engine to more stress.

This is car engine whose piston rings are rotten. Its valve springs are rusting off and its fuel injection system is all clogged up. Not only do we have no business racing this engine, but the very last thing we should do to it is add a turbocharger. That’s not what this engine needs. But the systems of the human body are so opaque to us, and the cultural narratives around athleticism so damaging, that this is exactly the position that we find ourselves maneuvered into—and outright believing.

Before the body is ready to be challenged with anaerobic exertion, the aerobic system must have achieved 3 benchmarks of competence: (1) as mentioned above, it must provide the overwhelming majority of the energy for the body’s basic upkeep, (2) it must be powerful enough to sustain a high level of brain function—while the muscles are hybrid engines, the brain is exclusively an aerobic animal—and (3) it must be able to adequately absorb the stresses incurred from present lifestyle.

When an underdeveloped aerobic system is being trained, any gains that are made will go towards securing the body’s basic upkeep: if there were chronic issues—such as carbohydrate intolerance, infections, etc—all gains will go first to combat those, and to make sure that they do not reappear. Speed will not increase.

Once that step is complete, any gains in aerobic function will go towards maintaining a high level of stable cognitive function throughout the day: if you had low or fluctuating energy levels, any gains will go towards stabilizing those. Speed will not increase.

And there’s the issue of present anaerobic function: if your your lifestyle or work demands a heightened level of focus, (or hell, you run two blocks with a backpack to catch the bus every day), your aerobic system will have to be that much more robust before it will be able to start contributing anything to your athletic output. Speed will not increase.

Phil Maffetone’s approach to health and athletic achievement does not just require us to develop the aerobic system. When discussing why our aerobic system is so underdeveloped, the Maffetone Method helps us realize that the present fitness culture (and the assumptions and beliefs that surround it) need a major overhaul.

Two people—one with a hugely powerful aerobic system and one without—will find that they have a very different “training response.” One will be able to tolerate a magnificent training volume, and one won’t. Present exercise science—and our own fitness instructors—will often tell us that the issue is genetic, or that we’re not good athletes. But a lot of times, that simply isn’t the case.