fitness · research

Why it doesn’t matter whether you exercise in the morning or evening

This week, the NY Times published an article with the headline “Is is better to exercise in the morning or evening?” The answer, when I dug into their article and the original research paper, was this: we learned many groovy facts about male mouse metabolism this week, but we still don’t know what time of day is best for you (a human) to exercise. Or even them (the mice), really.

Huh. You might be wondering why, after the NYT went to all the trouble to write this headline, that they don’t have an answer for us. And then there are those scientific researchers, who published this paper that shows a lot of results and many beautiful multicolored charts and graphs.

And yet. I maintain that we still don’t know what time of day is better for exercising. Why not? Here are some reasons.

No one has worked out and gotten other people to agree about what counts as a “better” or “best” time to exercise. Better in what sense? Feels best? Burns the most calories? Burns the least calories? Results in quickest muscle recovery? Contributes most efficiently to this or that training goal?

These are all really different ways to optimize on an exercise session. The researchers do mention time-dependent metabolic processes and effects on the mice-bros, but don’t offer general recommendations. The NYT article cites some studies (here and here) done on type-2 diabetic dudes (always and only the dudes… sigh) that show preferential effects from afternoon exercise. But that’s a particular sub-group, so the results don’t apply to everyone.

This study was done ON MICE. So, any effects they found, they found IN MICE. Yes, animal studies are common and often helpful in directing further investigation. But these results don’t tell us much of anything about humans. Which is no one’s fault, because the research subjects were MICE.

Mouse on a mouse-exercise wheel. Go mouse, go!
Mouse on a mouse-exercise wheel.

The study used only male subjects. In this case, it was male mice. Argh. So, if you’re a non-male person reading this, then you can’t know if the study results (if they had something even approaching advisory, which they don’t) apply to you. This is not a one-off case. Recall the research articles the NYT cited testing the metabolic effects of different exercise times on type-2 diabetes. They only used male subjects, too.

Woman fit to be tied, about to pull her hair out. Yeah, that's me.
Woman fit to be tied, about to pull her hair out. Yeah, that’s me (metaphorically).

What the research article never mentions and what the NYT saves until the end of their piece is the number one reason why it doesn’t matter whether I exercise in the morning or evening: the best time to exercise is the time I actually can and will and do exercise; it doesn’t matter when I move; it matters THAT I move. Here’s what the NYT said:

…as additional studies build on this one’s results, we may become better able to time our workouts to achieve specific health goals. Follow-up studies likely will tell us, for instance, if an evening bike ride or run might stave off diabetes more effectively than a morning brisk walk or swim.

But for now, Dr. Chow said, “the best time for people to exercise would be whenever they can get a chance to exercise.”

Yes, I can fully endorse that recommendation.

Readers, do you need to know what ways you can optimize on your physical activity? Do these results matter to you? Do you have your own optimal times, or do you mix it up in your workout schedule? I’d love to hear from you.

2 thoughts on “Why it doesn’t matter whether you exercise in the morning or evening

  1. Thanks for your analysis Catherine! I read this article earlier in the week and thought so what? But the extremely limited study of male mice stayed on my mind. And this morning on my bike ride (fueled by a pretty big breakfast) I thought “did the mice eat before they exercised?” Would that change the fat or sugar they burned? And because it was a little chilly–did the researchers control for temperature? Cold weather exercise burns more calories than hot weather exercise. I’m always disappointed in the NY Times when they publish these click-baity exercise articles that don’t really tell us anything. But I do agree with you and the researcher: the best time to exercise is when you can exercise!

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