When is the best time to exercise? The science of circadian rhythms has some clues.
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Jacobs Stock Photography Co., Ltd./Getty Images
When is the best time to exercise? The science of circadian rhythms has some clues.
Jacobs Stock Photography Co., Ltd./Getty Images
For years, I was in the habit of working out early in the morning. He was the type of person you would often see trudging to the gym as soon as the door was unlocked, or running around the neighborhood when the coffee shop was quiet.
However, this feeling of devotion rapidly disintegrated as the days progressed. In fact, training that deviates from your usual routine can feel almost unbearable.
Karin Esser recalls a similar experience in graduate school when she tried to run in the afternoon instead of in the morning.
“There were things that could be done, but I always felt like something was wrong,” said Esser, now chair of the department of physiology and aging at the University of Florida College of Medicine.
when you do that teeth What is the best time to exercise? The truth is, there is no scientific consensus. When you dig into the details, this question becomes surprisingly tricky. Who is exercising? What on earth are they doing? What is their goal?
Still, the past decade has seen a new wave of research into the interaction between exercise timing and circadian rhythms (our physiological and behavioral patterns that fluctuate over a 24-hour period). These advances have provided new insights into how workout timing impacts both health and athletic performance.
“A large part of our physiology is under the control of this molecular clock,” says Julien Zielas, professor of physiology at Karolinska Institutet in Sweden. “What we're trying to understand is how can we fine-tune the exercise prescription?”
Here are four discoveries from the latest science.
1. Exercise helps synchronize your body's circadian rhythms
If you've ever experienced jet lag, you've probably experienced a classic example of your body clock being out of sync, a phenomenon scientists call circadian misalignment.
But it's not just travel that confuses us.
All kinds of behaviors can disrupt your circadian rhythm, like staying up late on the weekend or eating at unusual times. This can be uncomfortable and, depending on how long it lasts, can have far-reaching effects on our health.
Circadian rhythms are not only related to the central clock in the brain. That's because every organ and tissue has its own molecular timekeeper, which scientists call the peripheral clock.
“Under normal conditions, our clocks are aligned and in the same time zone,” Esser explains. “The problem occurs when our clocks are off, so the brain's clock thinks it's here, and the liver and pancreas think it's something else.”
Light is the most powerful external time cue that aligns your circadian rhythm with the outside world, and is technically known as the zeitgeber. This is what the brain clock likes to follow and ultimately influences all kinds of biological processes and behaviors, especially when we wake up and go to bed.
Although not as powerful as light, exercise can also be a powerful signal for our circadian system, especially our peripheral clock.
This means that physical activity can be another tool to attune and synchronize your body to your sleep-wake cycle.
However, it is difficult to study exactly how this happens in the real world. This is because our bodies constantly listen to information from other times, such as light and food. Although the results aren't completely consistent, a recent clinical trial found that exercising in the morning or early afternoon may speed up your rhythm.
On the other hand, physical activity at night seems to slow down the clock, but this may not be the case for people with slow chronotypes, or night owls.
2. Muscles follow a clock and timing affects performance
Scientists have learned that the clocks within our cells are intertwined with the critical roles of their specific tissues and organs.
“Every cell in our body has a circadian clock,” says Katya Ramia, associate professor of molecular and cell biology at the Scripps Research Institute. “That means that so many aspects of our physiology differ depending on the time of the day.”
For example, the pancreatic clock is responsible for producing insulin, which varies throughout the day, and the liver clock regulates blood sugar levels and how certain drugs are metabolized, she says.
Then there's the muscle clock.
Esser, a pioneer in this field of research, said the muscle clock is key to guiding when cells take breaks for rest and repair, such as storing energy, and when they prepare for action. There is.
“Clocks are really part of homeostasis, taking care of business inside the cell,” she says.
As a result, these timekeepers are closely tied to our metabolism and how we use energy, with muscles playing a major role in things like processing glucose.
Scientists have discovered that the clock is involved in the pathway that uses sugar for energy and the pathway that transports that glucose from the outside of the cell to the inside.
The efficiency of mitochondria, the cell's powerhouses, also varies throughout the 24-hour cycle, with studies showing that it peaks in the late afternoon.
And these fluctuations in your muscles can affect your performance.
Their exact contribution isn't entirely clear, but they partly explain long-standing findings that people tend to lift the most weight, run the fastest, and break the most world records later in the day. may be explained.
This trend is “incredibly consistent,” Esser said.
Raphael Kneier, an exercise physiologist at the University of Basel in Switzerland who reviewed the evidence, said afternoon time is certainly the best. However, this study is primarily from young men and is of low quality, so it is still difficult to generalize. It is wonderful.
“Just because the afternoon is on average the best time for a certain population doesn't mean it's the best time for everyone,” he says.
Scientists speculate that everything from changes in core body temperature to hormones and neural activation may be responsible for this morning-to-afternoon fluctuation.
Muscle clocks are also a possible explanation.
“This evidence is highly suggestive that circadian clocks in muscles, and perhaps other organs, are important in driving differences in exercise performance,” Lamia says. “It just hasn't been proven yet.”
3. You may be able to shift your muscles' circadian rhythms to your preferred training time
In recent years, scientists like Esser have discovered that muscle clocks run on their own schedules. In fact, they respond very well to exercise.
Laboratory experiments on human muscle cells have shown that simply applying an electric shock to mimic movement “causes the muscle cells to twitch and generate force, which is enough to change the clock's settings.” Esser says this has become clear. Animal studies have shown that exercise actually overrides the effects of the brain clock.
Despite the data favoring the afternoon, preliminary findings from Dr. Esser's lab suggest that regular exercise in the morning can train the muscle clock to function similarly to that time of day. There are some interesting studies though.
The study found that mice that ran early in their active phase (which corresponds to our morning hours, since mice are nocturnal) had lower endurance levels than a group that ran during our afternoon hours. did.
But after using the treadmill at the same time every day for about 3 to 6 weeks, the “morning” runners performed just as well as the afternoon runners.
Analysis of muscle tissue showed that in the early groups, the muscle clocks shifted about four hours earlier, Esser said.
What is the impact?
“Clock phase is trainable,” she says, and you can change it to maximize performance.
This study has not yet been published and has limitations. The same carefully controlled, invasive experiments would be difficult to perform in humans. But the idea that consistency is important is also reflected in human data.
“There is good evidence that if you exercise regularly during the same times of the day, your performance tends to improve the most during those times,” Lamia says. This is why athletes prefer to train around competition schedules.
4. The secret to good health may lie in the timing of your exercise.
Even if you're not obsessed with being competitive, it's probably beneficial in the long run to exercise around the same times to adjust your body clock, Esser says.
“Clocks don't have to be accurate because they're not accurate. There's a two-hour, three-hour, sometimes four-hour window,” she says.
Scientists are also trying to pinpoint specific times when people with the condition may reap additional benefits.
Disturbances in circadian rhythms are associated with many health conditions, including cancer, diabetes, cardiovascular disease, and mental illness. This is believed to be the reason why night shift workers are at increased risk of all kinds of illnesses.
“If we can learn how to better synchronize our circadian systems, we may be able to prevent or reverse some of these health problems,” said Shawn Youngstead, a chronobiologist at Arizona State University. ” he says.
This latest frontier of research focuses on metabolic syndrome or diabetes.
There is strong evidence that disruption of circadian rhythms can wreak havoc on blood sugar and insulin. This can also occur in healthy people whose clocks become out of sync over a relatively short period of time. Several recent studies recommend afternoon exercise for people with type 2 diabetes and metabolic disorders.
“We're trying to use exercise to basically reset the rhythm of the muscle clock,” and in doing so “reset the metabolism,” said Zieras of the Karolinska Institutet.
A study in mice conducted by Geelas' team showed that exercising during the early morning hours in humans may be more effective at boosting metabolism and burning fat.
A study conducted by Zieras in men with type 2 diabetes found that while high-intensity training in the afternoon improved blood sugar levels, the morning session actually worsened blood sugar levels.
Other research supports exercising later in the day to help people with metabolic disorders, but this is not yet “scientifically established” because there are so many variables. Mr. Zieras emphasizes.
“Is this because we only studied men with diabetes? We also want to know what happens to people with normal glucose tolerance,” she says.
In fact, these results are not uniform, and other studies have actually found that mornings may be better for metabolic syndrome. For healthy people, evening exercise may improve blood pressure for men, but morning exercise is more effective for women.
“In general, we're at a fairly early stage in trying to understand this,” says Scripps Research's Lamia.
One thing, she says, is absolutely clear. She says, “I think the best time to exercise is when you actually exercise.”
