For years, I was an inveterate early morning exerciser — the kind of person you’d spot trudging into the gym just after the doors were unlocked or running through the neighborhood when the coffee shops were still silent.
But this dedication fell precipitously as the day progressed. In fact, any workout that deviated from my regular routine would feel almost excruciating.
Karyn Esser recalls a similar experience when she tried to run in the afternoon instead of the morning during graduate school.
“I could do it, but it always felt like something wasn’t right,” says Esser, now chair of physiology and aging at the University of Florida’s College of Medicine.
So when is the best time to exercise? In truth, there is no scientific consensus. The question gets surprisingly thorny as you drill down into the specifics. Who’s exercising? What exactly are they doing? What are their goals?
Still, the last decade has brought a wave of new research on the interplay between exercise timing and circadian rhythms — the patterns in our physiology and behavior that fluctuate over the 24-hour cycle. These advances have led to new insights about how the timing of your workouts can affect both health and athletic performance.
“There’s a great deal of our physiology that’s under this molecular clock,” says Juleen Zierath, a professor of physiology at the Karolinska Institute in Sweden. “What we’re trying to understand is how can you fine-tune the exercise prescription.”
Here are four findings from the latest science.
1. Exercise can help keep your body’s circadian rhythms in sync
If you’ve ever had jet lag, you’ve experienced the quintessential example of your biological clocks being out of sync — what scientists call circadian misalignment.
It’s not just travel that can throw us off, though.
All kinds of behaviors — like staying up too late on the weekend or eating at unusual times — can cause circadian disruption. This can feel crummy and can have far-reaching consequences for our health, depending on how long it lasts.
Circadian rhythms involve more than just the central clock in the brain, because every organ and tissue has its own molecular timekeepers, what scientists call peripheral clocks.
“Under normal conditions, our clocks are aligned — they’re in the same time zone,” explains Esser. “Problems arise when our clocks are misaligned, so the brain clock thinks it’s here, and the liver and the pancreas think it’s something else.”
Light is the most potent external time cue, technically known as a zeitgeber, that aligns circadian rhythms with the outside world. This is what the brain clock likes to follow, and that ultimately influences all kinds of biological processes and behaviors, most notably when we wake up and go to bed.
Though not as powerful as light, exercise can also be a strong signal for our circadian system, most of all for the peripheral clocks.
This means physical activity can be another tool to help get your body synchronized and lined up with its sleep-wake cycle.
Studying exactly how this plays out in the real world is tricky though, because our bodies are constantly hearing from other zeitgebers like light and food. While results aren’t entirely consistent, recent clinical trials have found that exercising in the morning or early afternoon can push your rhythms toward an earlier schedule.
On the other hand, evening physical activity seems to delay the clock, although this may not be true for those with later chronotypes — i.e., night owls.
2. Your muscles follow their clocks, and timing effects performance
Scientists have learned the clocks in our cells are intertwined with the important business of that particular tissue or organ.
“Every cell in our body has a circadian clock,” says Katja Lamia, an associate professor of molecular and cell biology at Scripps Research. “That means so many aspects of our physiology are different — at different times of day.”
For example, the clocks in our pancreas are involved in the production of insulin, which changes over the course of the day, while those in the liver are regulating blood glucose or how you metabolize certain drugs, she says.
Then there are the muscle clocks.
Esser, who has pioneered research in this area, says muscle clocks are key in guiding when the cell takes a break to rest and repair, including storing up energy, and when to get primed for activity.
“The clocks are really part of homeostasis and taking care of business in the cell,” she says.
Consequently, these timekeepers are closely tied into our metabolism and how we use energy, given that muscles have a big role in handling glucose, among other things.
Scientists have found that the clocks are involved in pathways that use sugar for energy and in transporting that glucose from outside the cell to inside.
The efficiency of your mitochondria — the power plants of the cell — also changes throughout the 24-hour cycle, with research showing a peak during the late afternoon.
And these fluctuations in our muscles may affect performance.
Read the full article by Will Stone / NPR
