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When is the best time to exercise?

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When is the best time to exercise?

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Exercising in the morning has vastly different effects on metabolism than the same workout later in the day, according to an ambitious new study on exercise timing. The study, which involved healthy lab mice jogging on tiny treadmills, mapped hundreds of disparities in the number and activity of molecules and genes in the rodents’ bodies, depending on whether they ran early in the morning or deeper in the evening.

Many of these changes were related to fat burning and other aspects of animal metabolism. Over time, such changes could significantly influence their disease risk and well-being. And while the study was in rodents, its findings are likely relevant to those of us wondering if training before work is better, or if it’s possible to get as much – or more – health benefits of exercising after hours.

As anyone with a body knows, our internal operations and those of almost all living creatures follow a well-orchestrated and pervasive 24-hour circadian rhythm. Recent studies in animals and humans show that almost every cell in our body contains some version of a molecular clock that coordinates with a larger and more comprehensive timing system to direct most biological operations. Thanks to these internal clocks, our body temperature, blood sugar, blood pressure, hunger, heart rate, hormone levels, sleepiness, cell division, energy expenditure and many other processes increase and slow down dramatically. repeated throughout the day.

These internal rhythms, while predictable, are also malleable. Our internal clocks can recalibrate themselves, according to research, based on complex cues from inside and outside of us. In particular, they react to light and dark, but are also affected by our sleeping habits and our meals.

Recent research suggests that the time of day we exercise also sets our internal clocks. In previous studies with mice, running at different times affected the animals’ body temperature, heart function and energy expenditure throughout the day and altered the activity of genes linked to circadian rhythm and aging.

Results in people have been inconsistent, however. In a small 2019 study of men who joined an exercise program to lose weight, for example, those who exercised in the morning lost more pounds than those who exercised later in the day, even though everyone performed the same exercise routine. But in a 2020 study, men at high risk for type 2 diabetes who started exercising three times a week developed better insulin sensitivity and better blood sugar control if they s trained in the afternoon than in the morning. These results echoed similar findings from 2019, in which men with type 2 diabetes who exercised intensely in the morning showed unexpected and undesirable spikes in their blood sugar levels after exercise, while the same workouts in the afternoon were improving their blood. sugar control.

However, few of these studies have ventured deep below the surface to examine the molecular changes driving circadian health and outcomes, which could help explain some of the discrepancies across studies. Experiments that looked at the effects of exercise at a microscopic level, usually in mice, tended to focus on a single tissue, such as blood or muscle. But scientists who study physical activity, metabolism and chronobiology suspected that the impacts of exercise timing would extend to many other parts of the body and involve a complex interplay between multiple cells and organs.

So for the new study, published this month as a cover story in Cell Metabolism, an international consortium of researchers set out to try to quantify nearly all of the metabolism-related molecular changes that occur during exercise. at different times of the day. Using healthy male mice, they jogged moderately on wheels for an hour early in the day, and others ran the same amount in the evening. An additional group of mice sat on locked wheels for one hour during these same times and served as a sedentary control group.

About an hour after the training sessions, the researchers took replicate samples of muscle, liver, heart, hypothalamus, white fat, brown fat, and blood from each animal and used sophisticated machines to identify and enumerate almost all molecules in these tissues related to energy consumption. They also checked for gene activity markers related to metabolism. Then they compiled the totals between tissues and between groups of mice.

Interesting patterns have emerged. Since mice are nocturnal, they wake up and become active in the evening and prepare to sleep in the morning, a schedule opposite to ours (unless we are vampires or teenagers). When the mice jogged at the start of their activity period – the morning equivalent for us – the researchers counted hundreds of molecules that increased or decreased in number after exercise, and which differed from the levels seen in mice running closer to bedtime or not exercising. at all.

Moreover, some of these changes occurred almost identically in different parts of the body, suggesting to the researchers that various organs and tissues were in fact communicating with each other. Rodent muscle and liver, for example, shared many molecular changes when the animals ran in the morning, but less when they ran shortly before bedtime.

“It was quite remarkable” to see how the timing of exercise affected the levels and activities of so many molecules in the animals’ bodies, said Juleen Zierath, professor of clinical integrative physiology at Karolinska Institutet in Stockholm, Sweden, and executive director of the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen, who oversaw the new study.

Overall, differences in molecular profiles between morning workouts (in mouse terms) and those later in the day tended to signal a greater reliance on fat than on blood sugar to fuel early exercise. The reverse happened when the mice ran in their evening. If these patterns were confirmed in people, it could suggest that morning exercise helps fat loss more, while late-day workouts might be better for blood sugar control.

But mice aren’t people, and we don’t yet know if the molecular models are true in us. The study researchers are working on a comparable experiment involving people, Dr. Zierath said.

This study was also limited in scope, examining a single session of moderate aerobic exercise in male mice. It does not show how other types of morning or evening exercise affect the inner workings of mice or humans. It also doesn’t tell us whether what we eat or when we eat, and whether chronotypes – whether we tend to be morning or evening people – play into these effects, or whether being a woman is important.

But even with its limitations, “this is a very important study,” said Dr. Lisa Chow, professor of medicine and endocrinology at the University of Minnesota, who was not involved in the research. It emphasizes the power of exercise at any time of the day.

It also suggests that as more studies build on the results of this one, we may become more adept at timing our workouts to achieve specific health goals. Follow-up studies will likely tell us, for example, whether an evening bike ride or run might ward off diabetes more effectively than a brisk walk or morning swim.

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

When is the best time to exercise?

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