NOTE: This is an unusually journal-entry-ish post for me. But I think it has some pretty useful concepts. I hope you like it. (Any mention of today refers to Friday, Sept 18, 2015).

For about 2 months now, I’ve been building my aerobic base under the MAF (Maximum Aerobic Function) principle, proposed by Phil Maffetone. I’ve seen an improvement of about 1 minute to my MAF pace—the speed at my aerobic heart rate, which is 148—and yet, I feel like today is the first day I really understood what running MAF is like.

The idea behind MAF training is to lower the intensity at which we train, in order for the aerobic base to kick in with theoretically no anaerobic function. This removes the majority of chemical stress associated which exercise, which comes from the release of hydrogen ions (H⁺). These ions acidify the body and create an added burden for recovery.

Training under this “aerobic threshold” allows the aerobic base to be developed quickly and efficiently. Typically, 3 to 6 month long period of exclusive MAF training strengthens the aerobic base to the point where it can efficiently absorb the stresses of high-intensity (anaerobic) exercise.

As editor on the MAF website, I answer a lot of difficult questions in the comment sections. For people are first calculating their MAF heart rate, a predictable question always pops up:

“Are you sure that my MAF Heart Rate is 148?” (or whatever). “This can’t be! I’m, like, really athletic. I stuck my first vault at 4 months of age. At two, I was running 5 minute miles. Are you sure it’s not at least 151?”

And honestly, I often feel exactly that way. It’s as if everyone (myself included) is trying to negotiate their way into a higher heart rate—thinking it is the highest possible heart rate (aerobic or otherwise) that will bring the most benefit.

I constantly tell commenters what it has taken until now for me to truly absorb: we have to lower the intensity to maximize the aerobic benefit. Trying to always be right on top of that aerobic threshold—what I’ve decided to call greenlining (as a riff on “redlining”)—is that very same high-intensity mentality, haunting a game that’s all about going low, not high.

Don’t get me wrong: when I run MAF—usually 1 hour, 5 days a week—I scrupulously bookend my workout with 15 minutes of warm-up and cool-down, in which I slowly and steadily bring my heart rate 3 or 4 BPM under my aerobic threshold.

Every warm-up, I notice the same thing: my heart rate oscillates its way up to MAF. It doesn’t climb steadily. Even once I do get close to MAF, it keeps oscillating. It goes up and down some 4 heart beats every 30 seconds or so, meaning that if I want to stay under MAF (which for me is 148) I have to stick with 143.

As a perfectionist, I always try to iron these things out. Maybe it’s fine for the heart rate to oscillate as long as it remains under MAF. But it’s still important to consider what oscillations mean. It means that metabolic work (and my speed) is rising and falling continually, when in theory we want to stay at the same metabolic output.

Maybe I’m overthinking this far and away, but to me this seems like a car lurching down the highway when a few tweaks to the engine would be all that’s needed to create a smoother ride.

Almost by accident, that is exactly what i did. It had been an uncharacteristically bad run: I went out after an hour of having eaten, and I just didn’t want to take my heart rate up there. I did my warm-up, and then dropped back down to 20 under MAF. I just felt like jogging.

As the minutes passed, my heart rate—and my speed—slowly began to increase, at a rate of about one beat per minute. And like that, over the next 20 minutes, I slowly approached MAF. My heart rate came to within 1 BPM, and for the next 40-45 minutes, held constant.

Today’s run was exceptional: I had far better joint stacking. It was extremely easy to keep my breathing in sync with my steps—three steps to an exhale and two to an inhale—and my breathing was also deeper than usual. The experience of running was one of incredibly little stress. When I did get up to MAF speed, I was faster by a full 15 seconds per mile.

And two hours after the run, I was full of energy, and my leg muscles, instead of feeling empty, felt warm and fuzzy. I’m not kidding.

But this makes perfect sense to me: calibration, not raw power, is the primary source of performance. Think of a 1000-horsepower engine with a timing belt that’s just a tiny bit loose. It can’t express a bit of that power. Think of that same engine attached to a gear box with all the wrong ratios, or mounted on a car whose tires are too pressurized. When that engine expresses all of its power, that car is going sideways.

Too often, as athletes and fitness enthusiasts we try to add horsepower when we should be checking the timing belt, or changing the stiffness of our valve springs. I think that in today’s workout—which feels like the highest-quality workout of my life—I enabled my body to focus on the small stuff . . . and get it right.

I’m willing to bet that this very long, very easy warm-up, which “sacrificed” time spent training at a higher intensity, was a central part of it. And I expect my bet to pay dividends in speed.

UPDATE: On Saturday I had an even more protracted warm-up. My speed increased by yet another 20 sec/mile.