“If exercise were a drug, it would be the best drug we have. . . .. But like with any drug, you’ve got to get the dose right.” — James O’Keefe

I’ve been wearing a continuous glucose monitor for the better part of the last few weeks.

It is perhaps the single best thing I’ve ever done for understanding my health. I’ll be writing several blog posts over the coming weeks with the lessons I’ve learned. The first few posts will be lessons I’ve learned about exercise.

Harder exercise isn’t necessarily better.

For most things in life, the relationship between effort and effect is linear. If we run harder, we go further. If we work harder, we make more money. Since this is how most things work, we apply this model to thinking about exercise.

However, when it comes to blood sugar and metabolic health, once we start burning calories faster than our aerobic system can handle it — things go a little haywire. Walking, swimming, gentle cycling, and even weightlifting where we are not losing our breath — these things lower our blood sugar consistently. Here are two recent examples. Note that blood sugar goes down and stays low after the workout (the light blue line ends because I ate afterwards).

Aerobic exercise feels like this:

You can breathe through your nose.

You can say a seven syllable sentence without taking a breath.

Your heart rate is below 180 — your age.

This is also known as “Zone 2” training, “Base training”, or “Maffetone Training”.

Here’s what happens to your blood sugar when you are anaerobic:

Notice that blood sugar does not go down. Your body is stressed, releasing cortisol, and dumping blood sugar into your system to make sure you survive.

In other words, hard/anaerobic exercise is STRESSFUL and RAISES blood sugar. And while a little bit of stress is good and helps you adapt, a lot is maladaptive. The research seems to bear this out: as exercise volume increases beyond moderate levels, lifespans actually go down.

And let’s remember that the person who pretty much invented high intensity training, Casey Viator, DIED AT 62 from a massive heart attack.

What’s the answer? Famous longevity expert Peter Attia suggests doing about 80% of your workouts aerobically. He says these are some of his “least favorite workouts”, since he is a Type A personality who loves to push hard.

Runner’s world suggests doing 80% to 90% of your training at this baseline/aerobic zone. Is this boring? A bit.

However, thanks to my CGM, I’m convinced that this is the right way to train for better health. In the next article, we will look at how and whether exercise can overcome bad diet choices.