You squeeze in a workout whenever your schedule allows, racing to a morning spin class, power walking at lunch or hopping on the treadmill after the sun goes down. While there is never a wrong time to exercise, there might be advantages to working out at certain times of the day.
In a new study published in the journal Cell Metabolism, co-author Paolo Sassone-Corsi, PhD, professor and director of the Center for Epigenetics and Metabolism at the University of California at Irvine, put mice on a treadmill and monitored changes in their muscle tissues. Morning workouts, he found, had the most significant impact on glucose breakdown and fat burning.
Sassone-Corsi believes a protein, HIF1-alpha, which influences circadian rhythms, also influences how your body responds to exercise at certain times of the day. He compares the different responses to exercise with the different responses to food.
“We know that eating the exact same food at midday and midnight has different impacts on your body,” he says. “Exercise is the same.”
MORNING WORKOUTS HAVE IT
Other studies have reported similar benefits to morning workouts: A new study published in the International Journal of Obesity found those who exercised in the morning lost more weight than those who waited until after 3 p.m. to break a sweat.
Anthony Hackney, PhD, a professor of exercise physiology at the University of North Carolina at Chapel Hill, believes hormones might influence how your body responds to exercise at certain times of the day: Levels of cortisol, the stress hormone, are higher in the morning and cortisol helps burn fat. In the evening, your cortisol levels drop, shifting your body into carbohydrate-burning mode.
“At the elite level, these small differences have the potential to have a big impact on performance and could mean the difference between winning a medal [or not],” Hackney says.
BUT THERE’S A TWIST
While average exercisers could benefit from working out in the morning, evening workouts might be better for elite athletes (or those aiming for a new PR).
A separate study, published in the same issue of Cell Metabolism, found mice that ran on treadmills in the evening used less oxygen, making their workouts more efficient. The result: You might be able to work out longer and at a higher intensity later in the day.
Shifting to a nighttime workout might also help reduce ghrelin, the hormone that controls appetite. As long as you’re not doing a hardcore workout in the hour before bed, Swedish researchers found evening workouts had no impact on sleep.
WHEN WEIGHT LOSS IS YOUR GOAL
If losing weight is your goal, scheduling your workouts in the morning or evening might not be as important as exercising around the same time each day, according to a 2019 study. Those who lost at least 30 pounds were more apt to maintain their weight loss if they maintained a consistent workout schedule, regardless of the time of day.
THE BOTTOM LINE
Hackney believes it’s interesting to research how small, subtle changes can influence how your body responds to exercise but cautions against getting too caught up in the science. Instead, he suggests exercising at the time of day that feels best for you.
“If you’re forcing yourself to ignore your internal clock, you might not be exercising at the right intensity or you might get bored and [cut your workout short],” he says. “There might be some physiological factors that make exercising at some times of day better than others, it’s more important to get out there and just do it than to obsess over scheduling a workout at the ‘right’ time of day.”