It found that, for women, morning workouts shed belly fat and improved blood pressure better than afternoon workouts. For men, nighttime exercise led to greater fat burning and better blood pressure control. Evening exercise also amplified the benefits of strength training, but more so for women.
Exercise timing studies are part of the burgeoning science of chronobiology, which focuses on how our internal clocks affect nearly every aspect of our physiology.
Human bodies, like those of other mammals, plants, reptiles and insects, function innately 24 hours a day. circadian rhythmwith a master clock system in our brains that sends and receives biochemical signals that coordinate with molecular clocks within our cells to direct an amazing symphony of biological processes.
This rhythm, in turn, responds to signals from the outside world, especially daylight and darkness, but also when we eat, sleep, and exercise.
Recent mouse studies it allowed large groups of rodents to run on exercise wheels at different times of the day. The studies showed that the animals’ heart rate, fat burning, gene expression, and body weight all change substantially, depending on when they exercise, even if the exercise itself is the same.
However, human studies on exercise time have been more conflicting. Some show that people burn extra fat and lose more weight exercising early, especially before breakfast, while others suggest that we get greater health benefits from the afternoon or night workouts.
But most of these studies were small, involving only men with metabolic conditions, such as type 2 diabetes, high blood pressure, or obesity. Therefore, we know little about the optimal time to exercise for healthy men, and even less about the best time for women. That’s why the new study is so significant.
A real-world study of exercise time
Published in May in Frontiers in Physiology, the research was designed to reflect real-world demographics, said Paul Arciero, director of the Laboratory of Human Nutrition, Performance and Metabolism at Skidmore College in Saratoga Springs, N.Y., and lead author of the study. .
All volunteers identified themselves as male or female, and more than half of the 56 participants were female. They were also all healthy and physically active, but not athletes.
The researchers assessed the volunteers’ health, strength and fitness and then randomly divided them into two groups, with equal numbers of men and women. One group was asked to exercise four times a week in the morning between 6 a.m. and 8 a.m. The other group was instructed to exercise in the evening between 6:30 and 8:30 p.m.
Each group participated in identical training. Once a week they lifted weights. The next day, they did about 35 minutes of interval training (running, swimming, or cycling as hard as possible for about a minute, rest, and repeat). Another day, they did yoga or pilates. They finished the week with about an hour of running, cycling, or other aerobic exercise.
The groups maintained this routine for 12 weeks and then returned to the lab for retesting.
Everyone in the studio was leaner, faster, fitter, stronger, healthier and more flexible, whether they exercised early or late.
Do you want to eliminate belly fat? Or build strength?
But there were relevant differences between the groups based on the time of day they exercised. This is what the researchers found:
- For women, fat burns best in the morning. Women who exercised early lost, on average, about 3 percent more total body fat than those who exercised at night, with much of the loss coming from their waistlines. Those who exercise in the morning shed about 7 percent more abdominal fat than women who exercise in the evening. (None of the volunteers’ total body weights decreased, as they gained muscle as they lost fat.)
- Morning exercise also lowered blood pressure in women who exercised significantly better than the same workouts at night.
- Meanwhile, the women’s nocturnal exercise increased strength gains. Overall, those who exercised at night improved upper body strength by 7% more than the morning group, and also performed more sit-ups and push-ups.
- For men, evening exercise was the clear winner in terms of health. Those who exercised in the evening significantly lowered their cholesterol levels, while those who exercised in the morning surprisingly raised them slightly. Evening exercise also boosted the men’s fat burning. At the end of the study, the bodies of men who exercised at night burned about 28 percent more fat during workouts than they did at the beginning, a change that can fuel body fat loss. The morning group’s fat burning increased only slightly.
- However, any time was the right time for men to increase their strength and fitness. Among the men, those who exercised in the morning and at night increased their strength in the bench press, leg press, sit-ups, push-ups and other strengths to the same extent, whether they exercised early or late.
What these results mean in practical terms is that women with specific health or fitness goals may want to fine-tune the timing of their workouts, Arciero said. If you’re a woman hoping to lose inches around the middle, consider morning workouts. If her goal is strength, night workouts may be more effective.
For men, exercising early or late seems comparable for strength and fitness, but nighttime exercise might have special health advantages, Arciero said.
Still, “it’s still early days when it comes to providing individualized recipes for the optimal time of day for exercise,” said John Hawley, director of the Nutrition and Exercise Research Program at the Australian Catholic University in Melbourne, Australia, who he has studied exercise metabolism and time, but did not participate in this study.
She noted that the new study did not control for the women’s menstrual cycles or track people’s chronotypes, whether they were naturally early risers or evening risers, both of which could influence responses to exercise. It also didn’t include midday exercise or investigate why men and women reacted so differently to exercise time. Arciero suspects hormones and other cellular and genetic effects, and plans follow-up studies to learn more, she said.
For now, the key takeaway from the study is that time can fine-tune what we gain from exercise. But we benefit regardless, so “whatever time of day you choose to exercise is the right time,” Hawley said.
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