And other new research indicates there may be unique benefits to exercising in the morning, suggesting that the best time to exercise depends on what we expect from a workout.
Why worry about when to exercise?
There is already a growing body of evidence that the health effects of exercise depend, to some extent, on when we are active. In previous research, people at risk for diabetes improved their blood sugar control more if they exercised in the evening than in the morning, while in other studies people lost more body fat if they exercised. exercise early rather than late in the day.
But most of these studies were small and their results narrow and inconsistent, so it’s been hard to draw conclusions about when we should exercise.
However, one of the new studies helpfully eliminates any concerns about study size. Published this month in Nature Communications, the new study brings together data from 92,139 men and women who had joined the UK Biobank, a UK adult health study, and worn an activity tracker for a week. .
Using the readings from the trackers, the researchers categorized the volunteers by how often and when they moved, checked mortality records up to seven years after people joined the Biobank, and compared the displacement patterns and deaths.
The strongest and least surprising correlation they found was that men and women who engaged in moderate or vigorous physical activity (the equivalent of brisk walking) most often lived longer than people who s rarely trained, no matter what time of day. got up and moved.
But the researchers also found subtle links between midday exercise and even better chances of a long life.
People who lumped in their physical activity between 11 a.m. and 5 p.m. or spread it out throughout the day were less likely to die prematurely from heart disease or other causes (except cancer) than people who primarily exercised. exercise before 11 a.m. or after 5 p.m.
This afternoon time, the researchers point out, coincides perfectly with the time of day when, statistically, people are least likely to suffer a heart attack.
The benefits of afternoon exercise for longevity were most pronounced for men and the elderly. But, overall, the findings suggest that the timing of exercise “may have the potential to maximize the health benefits of daily physical activity,” the researchers conclude.
Morning exercise targets body fat
But for many of us, afternoon exercise in the middle of the workday is either a logistical challenge or an unwanted temper.
For these people, a new study featuring healthy mice on tiny treadmills offers some hope.
The research builds on a separate, ambitious study last year in which researchers at Stockholm’s Karolinska Institute and other institutions listed almost every molecule that changed in the body tissues of mice, according to the when they ran.
To their surprise, they noticed that the changes were particularly pronounced in the fatty tissue of the animals. “We didn’t expect fat to be so affected,” said Juleen Zierath, professor of integrative clinical physiology at Karolinska Institutet and one of the study’s lead authors. She and her co-authors predicted that the animals’ muscles and liver, which help fuel exercise, would show the most molecular alterations.
So for the new study, they decided to focus on fat and how the timing of exercise changed it. They had male mice run for an hour on tiny treadmills or stand on the same treadmills as a control. Some ran for a few hours after waking up, which equals mid-morning for us.
Others ran a few hours after the start of the period when the animals would normally slow down and rest
Some of the animals skipped eating before their training; others nibbled beforehand on croquettes at will.
The researchers took blood and fatty tissue from the animals repeatedly in the hours after they exercised. And they found a lot more in animal fat that ran a few hours after waking up. Their fat released far more fatty acids, the building blocks of fat, into the animals bloodstream ready to be used as muscle fuel. And remnant adipose tissue showed greater increases in biochemical markers of heat production and mitochondrial activity than fat from evening runners (in mouse terms), as well as activity in some genes related to fat metabolism.
Indeed, a single exercise session early in the day created conditions in the animals’ fatty tissue that would likely lead to greater fat burning and loss over time than the same exercise in the evening, Zierath said. .
How to choose the best time to exercise?
“This study has identified some fascinating effects,” said University of Michigan professor Jeffrey Horowitz, who studies exercise and metabolism. He did not participate in the new study.
But it also complicates the question of when to train. Is afternoon exercise better if our goal is longevity, while morning exercise is better for shrinking our waistline?
In reality, any difference “will be marginal,” Zierath said.
After all, the greatest gains in the longevity study came from frequent activity, regardless of the time of day.
And any increase in fat burning after morning workouts would likely be small, Zierath said.
“We talk about tweaking,” she says. But, over months, years or a lifetime, “these small changes can be significant.”
So if you want to burn a little more fat with each workout and slowly reduce your body’s fat stores, there may be benefits to exercising before noon. But if your main goal is more life, then get up and move more during the afternoon, if possible.
But the most important thing is to get up and move.
Do you have a fitness question? E-mail YourMove@washpost.com and we may answer your question in a future column.