As part of my digression into the effects of exercise, I tested the effect of a 15-minute walk (= on a treadmill at about 2.8 miles/hour) twice more. Here are the results:

Here is the result (posted earlier) of the first test:

Here is a test of a 40-minute walk:

What do I learn from all this? For my omega-3 experiments, which might cover 6 hours, I should keep the walking involved under 15 minutes. If I want to get some sort of mental benefit from walking, I should spend 40 minutes or more. Less obvious is this: I take these results to indicate the existence of a mechanism that “turns up” our brain when we are doing stuff and turns it “down” when we are inactive. This suggests what Stone-Age activity consisted of: more than 15 minutes of walking. This also suggests that whatever the benefits of exercise, they require more than 15 minutes of walking to obtain.

The practical question these results raise is how to use this effect to help me with what I do all day — most of which, such as writing, seems to be incompatible with walking. Walking breaks every few hours? What about running 10 minutes every few hours?

Gary Taubes’ new book on food and weight comes out today. Taubes agrees with what I say in The Shangri-La Diet: Exercise is a poor way to lose weight. The results above provide a different reason to exercise, of course. But the details should change. My impression is that most people focus on burning calories; whereas these results suggest choosing exercise that best produces this reaction-time-lowering effect.

Exercise reduces reaction time, I’ve found. What’s the threshold? I wondered — how little exercise do you need to get the effect? I wanted to know so that in my omega-3 experiments, I could be active — e.g., walk to a cafe — without distorting the results. Also, for practical reasons, I wanted to produce the effect as easily as possible.

To learn more about the threshold, I walked on my treadmill for 15 minutes at a comfortable speed (2.8 miles/hour). Here’s what happened:

If anything, the short walk increased reaction time. Thirty minutes of walking produced a clear (and repeatable) decrease, so the the effect appears to require between 15 and 30 minutes of walking.

I did this experiment three days ago. Self-experimentation is many times easier than conventional science; blogging is many times easier than conventional publishing. A powerful combination, I hope.

How little exercise will produce the reaction-time-lowering effect I’ve found (here and here)? I decided to measure the effect of a 10-minute walk from a BART stop to a cafe. (Nicely integrating work and work.) But I got off BART at the wrong stop and my 10-minute walk took 40 minutes.

Here is what happened:

Just as with a 30-minute treadmill walk, the effect was delayed.

This is more support for the idea that exercise temporarily improves brain function. The novelty in this particular experiment is that the exercise was “real” rather than on an indoor treadmill.

For comparison, here are earlier results from much more strenuous exercise (30 minutes walking uphill on a treadmill):

The effect of more strenuous exercise was larger and lasted longer. With the easier exercise (the stroll) there was a downward spike in reaction time; with the more difficult exercise (the climb) there was a more crater-like effect. The spike shape suggests the effect was sub-maximal; the crater shape suggests that the maximum effect was reached. Which makes sense because the climb was close to maximum effort, whereas the stroll was far below it.

A kind reader pointed to a NY Times article on the brain effects of exercise. “Exercise can, in fact, create a stronger, faster brain,” says the article. “Create” refers to neurogenesis. The effects I’ve observed are more temporary — more like adding better fuel to a car.

“The human brain is extremely difficult to study, especially when a person is still alive,” says the article. Not entirely true.

During my omega-3 tests, I noticed that exercise seemed to be reducing reaction time (= better brain function). When I tested this, the results surprised me: Reaction time wasn’t lower immediately after exercise but became lower later. Did exercise have a delayed effect or was the shower I took soon after exercise responsible?

To find out, I did a little experiment. The earlier exercise was 30 minutes on a flat treadmill at about 2.8 miles/hour; this time I walked 30 minutes on a steep treadmill at higher speed (about 3.7 miles per hour). Here are the results:

Vertical lines show when the exercise started and stopped. This time there was improvement immediately after the exercise (unsurprising, given that it was much more intense) but even more improvement a half-hour later. I took a shower several hours later; it had no clear effect. The improvement lasted several hours before starting to diminish.

The data are very clear. They imply the earlier results can be believed: Exercise does improve brain function in an unanticipated way. Losing weight with exercise is hard; improving brain function with exercise appears easy. I want to study this effect in detail. Not only should it teach me how to improve brain function, it should also suggest the best dose of exercise for the rest of my body.