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  • For those who want a little extra from their workouts, exercising earlier in the day could be the way to go, at least according to a recent study in mice.
  • The new study gives us a better understanding of how the timing of exercise impacts metabolism at a specific tissue level.
  • But experts say the most important factor is to get the workout in, no matter what time of day it is.

When it comes to physical activity, all exercise counts, no matter what time of day you do it. And for many, the best workout schedule is whatever helps you move more often and regularly.

But for those who want a little extra from their workouts, exercising earlier in the day could be the way to go, at least according to a recent study in mice.

“Our results suggest that late morning exercise could be more effective than late evening exercise in terms of boosting the metabolism and the burning of fat,” study author Juleen Zierath, PhD, a professor in the Department of Molecular Medicine and Surgery and the Department of Physiology and Pharmacology at the Karolinska Institutet in Stockholm, Sweden, said in a news release.

While mice and humans have similar physiological functions, including metabolism, there are important differences between the two.

As a result, “more studies are needed to draw any reliable conclusions about the relevance of our findings to humans,” Dr. Zierath said.

In the study, published February 13 in the journal Proceedings of the National Academy of Sciences (PNAS), researchers studied the fat (adipose) tissue of mice after a session of high-intensity exercise performed during the early active phase and early rest phase of their daily cycle.

Mice are nocturnal, so their daily cycle differs from that of humans. These phases, though, correspond to morning and evening for people.

Researchers found that when mice did physical activity during the early active phase, there was an increased expression of certain genes, indicating a higher metabolic rate.

The affected genes are involved in the breakdown of adipose tissue, heat production (thermogenesis), and proliferation of mitochondria (the cellular “power houses”).

These effects did not occur when mice exercised during the early rest phase; they were also not affected by what the mice ate.

This study “revealed that the impact of exercise on metabolism in adipose tissue relies on when to exercise,” Shogo Sato, PhD, an assistant professor from the Department of Biology and the Center for Biological Clocks Research at Texas A&M University in College Station, told Healthline.

In particular, the results indicated “that the early active phase is the appropriate time of exercise for metabolic adaptation in adipose tissue,” Dr. Sato said.

He was not involved in this particular study, but has worked with the same group of researchers on related studies.

The new study was funded by the Novo Nordisk Foundation, the Swedish Diabetes Foundation, the Swedish Research Council for Sport Science, and the Swedish Research Council.

This research is a follow-up to a separate mouse study by Sato and some of the same researchers, published last year in the journal Cell Metabolism.

In that study, researchers measured the impact of exercise done at different times of day on blood samples and on different tissues, including brain, heart, muscle, liver and fat.

This provided them with a comprehensive “map” of signalling molecules that are present in different tissues as a result of exercise at different times of day.

Sato also pointed to another study in mice that he worked on with the same researchers, published in 2019 in the journal Cell Metabolism.

This research focused on skeletal muscle, which Sato said is “sensitive to exercise stimulation.”

In that study, researchers found that exercise during the early active phase had a strong impact on certain metabolic pathways, including glycolysis, lipid oxidation and the breakdown of branched-chain amino acids.

Overall, the new study and earlier research gives us a better understanding of how the timing of exercise impacts metabolism at a specific tissue level, said Sato.

This information could potentially be used to develop time-of-day-based exercise programs that improve metabolic function in people with type 2 diabetes or other metabolic diseases.

Along these lines, other research by Zierath and her colleagues has looked at whether exercising at certain times of day might benefit people with type 2 diabetes.

However, “an appropriate time of exercise in humans, depending on different disease risks, such as cardiovascular diseases and aging, is [not yet clear],” said Sato.

Before doctors can recommend that patients exercise at specific times of day, Sato said more research is needed to better understand the molecular mechanisms underlying the time-of-day-related impact of exercise on metabolism.

Haley Perlus, a peak performance coach with a PhD in sport and exercise psychology, said other research supports exercising at certain times of day.

For example, exercising at 7 am or between 1 and 4 pm may shift the body clock (aka circadian rhythm) to an earlier time.

This can make “your body naturally more alert in the morning and more tired during nighttime,” said Dr. Perlus, “helping you fall asleep earlier.” In turn, sleeping better can help muscles recover from exercise, she said.

In contrast, working out in the afternoon and early evening may be a good option for building muscle, she said, as a result of fluctuations in hormone levels and core body temperature at that time.

“Ultimately, the best time to exercise is whenever it’s most convenient and enjoyable for you,” she said. “That way, you’ll be motivated to commit to a routine.”

This depends not only on what else you have going on during your day, but also what type of exercise you do, she said.

For example, if you like to bike or run outside, exercising early in the day might not work, especially in the winter when it is dark and cold in the morning.

So, when thinking about your exercise schedule, “the most important thing is that you consistently work out, regardless of the time you choose,” Perlus said.