When is the Best Time of Day to Exercise?

I run 4 or 5 times per week, and I can assure you there’s no ideal time for it.

The weather is always too hot. Except when it’s too cold. Or it’s dark outside. Or I’m tired, or busy, or...

I ignore these inconveniences and run anyway.

Some people say I’m disciplined. The truth is that I’m stubborn. I love running and refuse to be distracted. Most afternoons I lace up my shoes, no matter what, and just go.

A study published last week suggests that I should be more flexible. The researchers found that exercise is most beneficial when it’s aligned with your chronotype.

In other words, if you’re a morning person, exercise in the morning. If you’re a night owl, exercise later in the day. The cardiometabolic benefits include lower blood pressure and LDL cholesterol, better sleep, and more gains in fitness.

I’m definitely a morning person. Have I been running at the wrong time? When is the best time of day for any of us to exercise?

The answer turns out to be more nuanced than what the new study tells us (not to mention what you might’ve heard about it from Good Morning America, U.S. News, the BBC, or one of the other news outlets that covered it).

Chronotype

A chronotype is one’s natural tendency to be asleep or active at certain times of day.

Morning people, or “larks”, tend to wake early and feel most energetic, mentally and physically, from the morning through early afternoon.

Evening people, or “owls”, tend to wake later (if their schedule permits) and feel most energetic in the late afternoon and evening.

Not everyone is so easily classified. Chronotype is normally distributed, which is to say that “larkishness” or “owlishness” is a matter of degree, and most people are found somewhere between the extremes.

If you’re lucky, your chronotype aligns with your work schedule and other obligations. Not everyone is lucky. “Social jet lag” occurs when a person’s chronotype is chronically misaligned with their daily schedule. This is almost always discussed in the context of owls forced to get up early for work, but exercise is another domain in which it can be seen.

For instance, a lark might feel most like exercising in the morning, while an owl might prefer that late afternoon or evening workout. But people can’t always exercise when they want. If we can, we might want to choose the healthiest option. The new study explores whether alignment between chronotype and time of day matters.

The new study

This study, led by Arsalan Tariq (University of Lahore) and colleagues at the Universities of Edinburgh and Ibadat, was published last week in the BMJ journal Open Heart.

Participants ranged in age from 40 to 60 and had no major health problems other than at least one risk factor for cardiovascular disease (prehypertension/stage 1 hypertension, overweight/obesity, sedentary lifestyle, impaired fasting glucose, and/or a family history of premature CVD).

These are Pakistani adults, but it’s hard to imagine a sample of greater relevance for Americans. More than three-quarters of us have one or more of those risk factors.

The researchers determined chronotype by means of the Morningness-Eveningness Questionnaire (MEQ), a widely used tool, and by 48 hours of continuous temperature monitoring. (Larks show predictable rises, peaks, and falls in body temperature earlier in the day than owls do.)

Participants came to the University of Lahore five days per week for a total of 12 weeks. Each 40-minute exercise session at Lahore consisted of supervised, moderate-intensity walking.

Exercise sessions were offered in the mornings (8 to 11 a.m.) and evenings (6 to 9 p.m.). And here’s a critical detail:

• Half the participants were assigned to sessions that aligned with their chronotype. (Morning people exercised in the mornings; evening people exercised in the evenings.)

• The other participants were assigned to sessions that conflicted with their chronotype. (Morning people exercised in the evenings. Evening people exercised in the mornings.)

Main findings

1. By week 12, everyone improved on every outcome variable: Blood pressure, LDL cholesterol, quality of sleep, fitness, etc.

No surprise there. Regardless of time of day, regular exercise is good for you.

2. By week 12, the extent of improvement was significantly greater for the chronotype-aligned group than for the chronotype-misaligned group.

In other words, people benefitted most when the timing of exercise matched their chronotype, regardless of whether they’re larks or owls.

The table below shows how much people gained on average from alignment. (”Benefit of alignment” is the chronotype-aligned mean minus the chronotype-misaligned mean.)

On the face of it, these are dramatic findings. Exercising at the time of day that suits your chronotype improves cardiometabolic health and fitness more than exercising at the “wrong” time does.

Some qualifications

If you’re exercising at a time that doesn’t match your chronotype, you might benefit from an adjustment, but I wouldn’t feel pressured to change anything.

Why not?

1. Small payoffs.

The benefits of chronotype-consistent exercise seem small, especially considering that people needed 12 weeks of 40-minute walks, 5 days per week – plus any walking to and from the lab – in order to achieve them. (In the table above, none of the changes would be considered clinically meaningful, other than that 5.3 mmHG drop in systolic blood pressure.)

I don’t mean to downplay the benefits. I’m just not sure they call for changes to anyone’s schedule.

Keep in mind too that changing your schedule isn’t an isolated act. An owl who exercises in the evening and then eats a heavy meal at 10 p.m. may be undermining their sleep and cardiometabolic health. Ditto for the lark who gets up too early to exercise.

I run in the afternoon, around the time my window of peak energy is starting to close. Sometimes I feel alert, sometimes a little drowsy. But I don’t plan to start running after breakfast, because mornings are when I get the most accomplished. I wouldn’t want to stay up late finishing tasks I could’ve done more quickly and pleasantly earlier in the day.

2. Confounds.

Chronotype is reflected in physiological states we rarely notice, like slight shifts in body temperature, as well as a whole bunch of stuff that we are aware of, like how alert and energetic and motivated we feel.

Exercising at a chronotype-inconsistent time can feel mildly unpleasant, like you’re doing a chore. You probably don’t exercise with as much intensity.

Thus, this study might not show that chronotype-consistent exercise per se is beneficial. Rather, what’s best is exercising when you enjoy doing it, because you’re investing more energy and reaping greater rewards. Enthusiasm rather than timing may be the critical variable.

There’s plenty of evidence that people exercise more – and more intensely – when they like what they’re doing. Chronotype-aligned exercise may be desirable only because that’s when we tend to be most enthusiastic about it – which is to say that exercising at the “wrong” time of day for you might still be just as good if you enjoy the activity.

A suggestion…

I wouldn’t call myself a poster child for healthy living – cookies are never safe in my presence – but I do recommend my attitude toward running, which is to ignore anything that diminishes the pleasure of the activity.

I don’t psych myself up for a run. I just focus on the sensations and the scenery and tune out the noise.

(Of course, you shouldn’t ignore the kinds of pain that signal a developing injury. I’ve tried that, and it rarely turns out well. Also, if you run, don’t ignore stop signs, potholes, and other people.)

And a final thought…

For years, scientists (and everyone else) debated the merits of morning vs. afternoon exercise.

Attention to timing-chronotype alignment, rather than focusing exclusively on time of day, represents progress – even if it turns out that enthusiasm is the key variable.

Still, we don’t want to lose the forest for the trees. Regular physical activity is healthful, regardless of whether the conditions are ideal. Almost anything that gets your heart pumping and strengthens your muscles will be good for you (see the CDC guidelines, for instance).

Diversity in physical activity is worthwhile too, as I discuss here. If you can coordinate exercise with your chronotype, great, but it’s not essential. Just find your enthusiasm, and, as James Brown put it, get up offa that thing!

Thanks for reading!