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by Elaine K Howley

April 25, 2022

Certain times may help you meet your goals more efficiently, but any time is better than no time

Early mornings have long been the domain of most Masters swimming workouts. Many adult swimmers find that getting up at the crack of dawn to log laps fits better with busy work and home schedules.

But depending on your goals for such exercise, new research suggests that you might want to consider hitting up an afternoon workout session instead.

A small 2020 study conducted in Holland examined how exercise timing affects metabolic changes. The study of 32 adult males who had been diagnosed with or were at risk of developing Type 2 diabetes undertook 12 weeks of supervised exercise training in either the morning or the afternoon.

When the researchers compared the data between the morning exercisers and the afternoon exercisers, they found that participants who trained in the afternoon “experienced superior beneficial effects of exercise training on a variety of disease markers.” These men also dropped a bit more weight from the abdomen than their morning-exercising counterparts.

These results, part of a growing body of research about timing of exercise, suggest that people who are “metabolically compromised,” meaning they have or are at risk for diabetes or have other metabolic conditions, “may reap more pronounced metabolic benefits from exercise training when this training is performed in the afternoon versus morning.”

These results echo those from a 2019 study conducted at the Karolinska Institutet in Sweden, which found that 11 men with Type 2 diabetes achieved better blood glucose control when they engaged in high intensity interval training in the afternoon. By contrast, when those study participants performed the same exercise routine in the morning, it actually spiked their blood sugar levels.

It’s worth pointing out that both studies involved only male participants, so it’s not clear whether the results will hold true for women.

Time to Move

Why exactly afternoon exercise appears to help with blood sugar control is not fully understood, but circadian rhythm—the body’s internal clock—is likely a key factor. Scientists have long understood that the circadian clock and metabolism—and the intricate web of hormones involved with it—are connected. But how exactly and how to leverage both for better health is still mostly an open question.

Much of the research conducted so far into the circadian rhythm has focused on the timing of food intake and sleep. Whether and how the timing and duration of exercise could influence metabolic health poses exciting questions that could not only improve health but aid athletic performance.

What’s Your Aim?

Although the science is still in early stages, it seems the question of when it’s best to exercise will likely be guided by another question: “Why do you exercise?” If your goal is to lose weight, another 2019 study suggests that working out in the morning may provide a better fat-burning boost to your efforts.

If your aim is to perform your best in the pool, several studies have suggested that an evening session might be best. For example, a 2007 study looked at swim performance specifically and tested the previously reported theory that performance peaks in the early evening. A group of 25 swimmers—13 female and 12 male—were assessed over 50 to 55 consecutive hours.

The complex study involved swimmers following a three-hour ultra-short sleep-wake cycle—one hour of sleep in darkness and two hours of wakefulness in dim light. They then swam six all-out effort 200-meter trials distributed equally across eight times of day. Each trial was separated by nine hours. The researchers controlled for environmental factors and found that “swim performance across all participants differed significantly by environmental time of day,” with swim times between 2 a.m. and 8 a.m. being significantly worse than those conducted at other times of day. Peak performance was noted at 11 p.m.

However, individual variation seems to play a role as well, at least according 2015 study published in Current Biology that found “personal best performance times differ significantly between circadian phenotypes.” Circadian phenotypes is a more scientific way of saying that one person is a night owl while another is an early bird.

Although the science may be confusing, across all these studies, one thing seems clear: At the end of the day (pun intended), whatever exercise time fits in with the rest of your life is probably best. Regardless of whether you’re trying to swim fast, lose weight, or regulate your blood sugar, when it comes to moving your body, doing something is nearly always better than doing nothing. And that’s worth getting up before the sun to achieve. 


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