DEAR DOCTOR K:
I do both aerobic exercises and resistance (strength) training exercises. Recently I heard that aerobic exercise might be better for the brain. Is there any truth to that?
You probably are referring to a study published in February 2016 that got a lot of media attention. Before getting into the details of that study, it’s worth talking more about exercise and the brain.
It’s no surprise that exercising your muscles keeps them (and the heart and lungs) in shape. And it’s no surprise that exercising the brain — like doing puzzles, learning a new language, etc. — may keep the brain in shape. What many people don’t know is that regular physical exercise may also benefit the brain, along with the muscles, heart and lungs.
The evidence for this is clearest in animals. It is less clear, however, in humans. For example, studies of people who exercised regularly for eight to 26 weeks could find no clear brain benefit. I would argue, however, that you wouldn’t expect to see brain benefits in that short a time.
In fact, this is an example of why it can be so hard to study human beings. Let me explain. If I were to design an ideal study of the effects of exercise on the brain, I would recruit at least a thousand human beings. I’d study their brain function in detail, at the beginning and end of the study, to look for changes.
Then I’d assign them, at random, to either exercise every day or to never exercise — every day, for 10 to 20 years. And I’d check in every day with each of the thousand people, to be sure they were either exercising or not exercising. I think you can see how difficult it would be to perform my ideal study.
Because human studies are hard, the study you heard about used rats — mammals like us. Their brains are built like ours, although smaller, of course. Rats don’t live long, so you can study them for a good fraction of their life span. And, at the end of the study, you can take out their brains and count the number of brain cells. Humans won’t let you do that.
The study put the rats through one of four programs: regular, sustained aerobic exercise; high-intensity interval training (HIT); resistance training; or just a constant non-exercising (sedentary) state. Upon completion of these programs, researchers counted the number of brain cells in a part of the brain that is important in memory.
The three different types of exercise were compared to the sedentary state. The regular aerobic exercise group of rats had more brain cells. That was not true of the high-intensity interval training or resistance-training groups.
The question is whether such a study in rats offers lessons to us humans. We just don’t know. But I think that it could. So I’ve voted with my feet. Instead of four aerobic and three resistance-training exercises each week, I’ve switched to five and two. Who knows? Maybe it will help.