A debate has raged for years over whether it’s better to exercise in the morning or evening. New research suggests there’s not a simple one-size-fits-all answer.
“In clinical practice, we see that patients respond differently to the same exercise programs,” says the lead study author, Arsalan Tariq, DPT, a researcher at the University Institute of Physical Therapy at the University of Lahore in Pakistan.
“I was interested in whether timing of exercise, based on an individual’s natural body clock, could help explain these differences and improve outcomes in patients at cardiovascular risk.”
“The key novelty is showing that when you exercise matters, not just how often or how intensely,” Dr. Tariq says.
The findings “suggest a strategy to help us optimize the beneficial effects of exercise,” says Cheng-Han Chen, MD, an interventional cardiologist and the medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, California, who was not involved in the study,
For Clues About the Best Time to Exercise, Look to Your Sleep Schedule
All participants were ages 40 to 60 and had at least one risk factor for heart disease, such as being overweight or having obesity or high blood pressure. They also reported doing very little or no structured exercise in the previous three months.
Researchers randomly assigned the participants to exercise at a time that matched their chronotype — between 8 am and 11 am for early birds, or between 6 pm and 9 pm for night owls — or at a time that didn’t match it. During their allotted time, participants completed 40-minute brisk treadmill walking sessions in a lab, five days a week for 12 weeks.
Once before the trial started, and again three days after workouts concluded, researchers took these measurements:
Overall, 134 participants completed all 60 exercise sessions. Of those, 70 were early birds and 64 identified as night owls.
After analyzing the data, the researchers found that participants in both groups saw improvements in heart disease risk factors, aerobic fitness, and sleep quality after 12 weeks. But participants whose chronotype matched with exercise timing had greater improvements in blood pressure, heart rate, aerobic capacity, metabolic markers, and sleep quality than those who didn’t work out around their chronotype.
The biggest improvements were in sleep quality and systolic blood pressure. In the chronotype-aligned group, sleep quality improved by 3.4 points, compared with a 1.2 point improvement for the unaligned group.
Systolic blood pressure — the maximum pressure against artery walls when the heart beats and contracts, and the top number in a blood pressure reading — fell by 10.8 mm/Hg in the aligned group, compared with an average 5.5 mm/Hg drop in those who were mismatched.
Participants who had high blood pressure at the start of the study saw an even larger drop in systolic blood pressure.
There Are Likely a Few Things Behind the Extra Benefits
The study didn’t explore the reason for this link; it merely found an association. But there are a few theories.
“It may be that people with disruptions to their natural circadian rhythms, such as those with irregular work and sleep schedules, benefit from exercise that properly matches their circadian timing,” Dr. Chen says. “Or it may simply be that people are more motivated and exercise better when the timing of assigned exercise corresponds to their preferred time.”
Tariq says matching your exercise timing to your body clock reinforces your circadian rhythm and makes the process of working out more seamless.
“The body operates on a circadian rhythm that regulates heart function, hormones, metabolism, and sleep,” he says. “When exercise is performed at a time that matches this rhythm, the cardiovascular system responds more efficiently, hormonal balance is optimized, and sleep patterns improve.”
When exercise happens at a time that’s not aligned with a person’s body clock, it “may create physiological stress and reduce these benefits,” Tariq says.
Circadian Rhythms Are Closely Linked to Physical Activity and Heart Health
“Exercise serves as a cue for the body to help it align the underlying circadian biological signals,” Chen says. Disrupting that internal clock can impact the regulation of vital systems that control heart rate, blood pressure, and metabolism.
“Over time, this can then lead to high blood pressure and obesity, which may potentially result in increased risk of developing heart disease,” he says. “And of course, we know that physical inactivity is itself a risk factor for heart disease.”
The Study Has a Few Limitations
Participants in the study were recruited from government hospitals in Lahore. As a result, the findings may not apply to people from different countries or people of different ages.
The study also excludes any potential participants who had an “intermediate” chronotype, meaning they didn’t fit neatly into early bird or night owl groups.
Doctors Recommend Listening to Your Body
“We often tell people to exercise more, but we rarely tell them when to do it,” Tariq says. “Our findings suggest that listening to your body’s internal clock can make a real difference.”
If you can only work out at a time that doesn’t align with your chronotype, Chen still recommends doing it when you can. “Any exercise is better than none,” he says. “We are just beginning to learn how the timing of exercise during the day can make it even more effective.”
But if given the choice, Tariq suggests trying to match your exercise time to your chronotype. “By exercising at the time your body is naturally most ready, you can improve your heart health, sleep better, and make exercise feel easier to maintain,” he says.