Morning exercise has vastly different effects on metabolism than the same workout later in the day, according to an ambitious new animal study on exercise timing. The study, which involved healthy lab mice jogging on tiny treadmills, mapped hundreds of disparities in the number and activities of molecules and genes throughout the rodents’ bodies, depending on whether they ran first thing in the morning or later at night.
Many of these changes are related to fat burning and other aspects of the animals’ metabolism. Over time, such changes could substantially influence your health and disease risks. And while the study involved rodents, its findings are likely to have relevance to any of us wondering if it’s better to exercise before work, or if we could get as many, or more, health benefits from exercise after hours of work.
As anyone with a body knows, our internal operations and those of almost all living things follow a well-orchestrated and pervasive 24-hour circadian rhythm. Recent studies in animals and people show that almost every cell in our body contains a version of a molecular clock that coordinates with a larger body-wide time 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 decrease in repeating patterns throughout the day.
These internal rhythms, while predictable, are also malleable. Our internal clocks can recalibrate themselves, research shows, based on complex signals from inside and outside of us. In particular, they respond to light and dark, but are also affected by our sleeping habits and when we eat.
Recent research suggests that the time of day we exercise also tunes our internal clocks. In previous studies in mice, running at different times affected the animals’ body temperature, heart function and energy expenditure throughout the day and altered the activity of genes related to circadian rhythm and aging.
The researchers had the mice jog moderately on wheels for an hour early in the day and others jog the same amount at night.
However, results in people have been inconsistent. 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 at the end of the day, despite all completing 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 blood sugar control if they exercised in the afternoon than in the morning. morning. Those results echoed similar findings from 2019, in which men with type 2 diabetes who exercised vigorously first thing in the morning showed unexpected and undesirable spikes in their blood sugar levels after exercise, while same afternoon workouts improved his blood. sugar control
However, few of these studies ventured deep below the surface to analyze the molecular changes that drive circadian and health outcomes, which could help explain some of the discrepancies from study to study. Those experiments that examined the effects of exercise at the 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 decided 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, some moderately jogged on wheels for an hour early in the day and others ran the same amount at night. An additional group of mice sat on locked wheels for one hour during these same times and served as a sedentary control group.
Approximately one hour after the workouts, the researchers took repeated samples from each animal’s muscle, liver, heart, hypothalamus, white fat, brown fat, and blood and used sophisticated machinery to identify and enumerate nearly all of the molecules. in those tissues related to energy use. They also checked gene activity markers related to metabolism. They then tabulated the totals between tissues and between groups of mice.
The study investigators are working on a comparable experiment involving people
Interesting patterns emerged. Since mice are nocturnal, they wake up and wake up at night and get ready to sleep in the morning, a schedule opposite to ours (unless we’re vampires or teenagers). When the mice jogged at the beginning of their active time, equivalent to morning for us, the researchers counted hundreds of molecules that increased or decreased in number after exercise, and that differed from the levels seen in mice that ran closer to the hour. going to bed or not exercising. absolutely.
Furthermore, some of these changes occurred almost identically in different parts of the body, suggesting to the researchers that various organs and tissues were indeed communicating with each other. The muscles and livers of rodents, for example, shared many molecular changes when the animals ran in the morning, but fewer when they ran shortly before bed.
“It was quite remarkable” to see how the timing of exercise broadly affected the levels and activities of so many molecules throughout the animals’ bodies, said Juleen Zierath, a professor of integrative clinical physiology at the Karolinska Institute in Stockholm, Sweden, and executive director from the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen, who oversaw the new study.
Overall, the differences in molecular profiles between morning workouts (in mouse terms) and those done later in their days tended to indicate a greater reliance on fat than blood sugar to drive early exercise. The opposite occurred when the mice ran at dusk. If those patterns held true in people, it might suggest that morning exercise contributes more to fat loss, while later-day workouts might be better for blood sugar control.
Follow-up studies are likely to tell us whether an evening bike ride or run can prevent diabetes more effectively than a brisk morning walk or swim.
But mice are not people, and we don’t yet know if the molecular patterns hold true for us. The study investigators are working on a comparable experiment with people, Dr. Zierath said.
This study was also limited in scope, as it examined a single session of moderate aerobic exercise in male mice. It doesn’t show how other types of morning or evening exercise affect the inner workings of mice or people. Nor does it tell us whether what we eat or the time of day we eat, and whether chronotypes (whether we tend to be morning or evening people) play into these effects, or whether being female is important.
But even with its limitations, “this is a very important study,” said Dr. Lisa Chow, a professor of medicine and endocrinology at the University of Minnesota, who was not involved in this research. She underlines the power of exercise at any time of the day.
It also suggests that as additional studies build on the results of this one, we may be better able to time our workouts to achieve specific health goals. Follow-up studies are likely to tell us, for example, whether an evening bike ride or run can prevent diabetes more effectively than a brisk morning walk or swim.
But for now, Dr. Chow said, “the best time for people to exercise would be whenever they have the opportunity to do so.” – This article was originally published on The New York Times
