Can we hack into the biological clock that helps dictate our sleep cycles to get more out of our exercise routine?
We’re not there just yet, but recent research is shining new light on the interplay between the body’s circadian rhythm and physical exertion.
A pair of studies
“We were expecting exercise, just like other forms of modification of our physiology, would be more beneficial, or have a stronger impact, at different times of day and night,” Paolo Sassone-Corsi, PhD, director of the Center for Epigenetics and Metabolism at the University of California Irvine and senior author of one of the papers, told Healthline.
“We just didn’t know when, and the simple fact that we did this demonstrates that the clock itself is rewired, or reprogrammed, by exercise in different ways — whether you do that during the day or during the night. We were expecting it, but this has never been done before,” Sassone-Corsi explained.
The two studies looked at lab mice, along with 12 humans. Mice are nocturnal and seemed to get the most benefit from exercising toward the end of their active time — “mouse evening,” in other words.
Humans, meanwhile, are diurnal, meaning they’re active during the day. However, similar results were found between people and mice in the study.
It’s too early to definitively say what time of day is best for effective exercise, but the research does help flesh out how circadian rhythms affect the body.
It’s long been understood that the human body undergoes hormonal changes throughout the course of a circadian cycle.
“We know a lot of things that do change from hour to hour. Some hormones change reliably. Everybody has a built-in body clock,” Dr. Steven Feinsilver, director of sleep medicine at Lenox Hill Hospital in New York, told Healthline.
“It affects a lot more than just sleep. Lots of hormones change by the clock. Growth hormone is produced in the middle of the night while cortisol is produced in the early morning,” he said.
Based off this, Feinsilver says it makes sense that certain times of day might work better than others for meeting specific exercise goals.
Still, exercising at times the body is unaccustomed to has the potential to disrupt the body’s natural rhythms.
“A lot of people generally find it difficult to do vigorous aerobic exercise in the evenings and go to sleep,” said Feinsilver. “Might be a great time to exercise in terms of burning calories, but it might be hard to fall asleep after that. Not for everybody, but for a lot of people.”
A 2018 study on National Football League (NFL) athletes dovetails with these two more recent studies.
Data suggests that NFL teams tend to play better during night games (starting at 8 or 9 p.m.) than they do in day games (starting at 1 or 4 p.m.), likely due to circadian rhythms.
There are complicating factors — notably, frequent travel and time zone changes.
But the preliminary findings would appear to fall in line with data suggesting that early evening is the best time for effective exercise.
Humans are naturally diurnal, but many people don’t rise with the sun and go to sleep at night, due to shift work or general sleeplessness.
When it comes to establishing a good sleep pattern — even for shift workers who sleep during the day — the best bet is to utilize the body’s natural reaction to light.
“When you want to wake up at night, find any light you can to put on, or even park yourself in front of a light box to produce full spectrum light for maybe 20 minutes or so,” advises Feinsilver. “And if you’re driving home from work in the morning, wear the darkest sunglasses you can find. If you’re trying to get to sleep in the morning, you don’t want any light, so you need a very dark bedroom.”
It also helps to get the body moving once you get out of bed.
“People who aren’t sleeping very well should take the time to wake up in the morning, get exposed to light, and exercise,” said Feinsilver. “For most people, we tell them to get up, get out of bed, and walk outside. That’s a natural way to wake people up.”
It can be tough maintaining good sleep hygiene. But setting a consistent time to wake up in the morning — no matter how badly you slept the night before — is one way to improve sleep hygiene.
“Nobody can keep a perfect schedule. But the closer you can get to that, the better,” said Feinsilver. “Rule number one is that if your sleep is OK, you can do whatever you want. Nobody has to follow all the rules, necessarily. But if you’re not sleeping well, go back to the basic rules for sleep.”
Following these rules isn’t always easy — particularly when a Netflix binge occupies you long into the night. But the rewards are self-evident.
“You’ll feel better, sleep better,” said Feinsilver. “Sleep is a biological drive. If you don’t mess it up, it tends to work. But we mess it up all the time, and the major way we mess up is not keeping a consistent schedule.”
As researchers tease out more details about the body’s circadian rhythms, more data will be added to the existing body of knowledge.
Sassone-Corsi says he and his colleagues intend to continue delving into circadian rhythms, with the next study incorporating bloodwork.
“The study we just discussed looks at what happens in the muscle,” he said. “But the question is: what happens in other tissues? Is exercise having a similar or different type of effect in the fatty tissues, in the gut, in the brain? How much of that can we reveal by looking at the blood? This is what we’re doing right now.”
Researchers are finding more details on the connection between exercise efficiency and time of day.
There isn’t enough data to recommend exercising at one time or another, but researchers say evening might be the best time to get in your workout.
They also say it’s also important to recognize the role that circadian rhythms play in sleep hygiene.