How do you know what is the best time of day to work out? The only way to figure out if you should work out in the morning or evening is by your chronotype and your own personal circadian rhythm.

If you are trying to get or stay fit, you might have asked yourself: What is the best time of day to exercise?

“Morning," is what most people think, especially those who have completed their 5K run by 8 a.m. But night owls would disagree — they barely manage to slip on socks by that time.

Yet the answer is not quite as simple as that. Actually, the question is not as simple as that.

It's not, "when is the best time of day to exercise," but "when is the best time of day to exercise for you."

What Is Your Chronotype?

A chronotype is an “expression of individual circadian rhythmicity, which is related to sleep, diet, and physical activity patterns, including exercise," according to a recent study in Nature.

In other words, our circadian rhythm is our 24-hour cycle of sleep/wake and eating/exercise, but our chronotype is our innate clock, influencing our tendency to be a “morning lark" or a “night owl" — regardless of the hours we have to keep.

Before I tell you if it's possible to match your exercise to your circadian rhythm and chronotype, let me tell you about my morning exercise experiences.

The Power of When: My Morning Marathoning

When I was training for a marathon, all of my workouts and races were in the morning. I trained once a week with a group of a few dozen people, who chatted about their lives as we ran. I missed most of their stories as I felt like I only woke up at about mile five.

Back then, I was not a morning person .

We would all participate in smaller races, including 5Ks and 10Ks, and all of them started at 7 or 8 a.m., which meant I had to haul myself out of bed at 6 a.m.

One race, however, was slated for the afternoon, at 4 p.m. Out of all the runs I completed, I remember this one because I wasn't tired. In fact, it was my best time ever as I felt like I zipped through it.

I guess with my late-night schedule, afternoon exercise was better for me.

Can Exercise Change Your Type?

Some studies show that morning workouts can help you adjust your cycle. Researchers had sleep-deprived teenagers with a late chronotype (is there any other kind?) gradually move up their 45-minute exercise routine by 30 minutes each day for five days. Their circadian rhythm was adjusted by almost 30 minutes (although their chronotype did not change.) The study showed the “preventative effect of low-intensity morning exercise."

As a mom with a young kid, I have also had to shift my wake-up times like those sleep-deprived teenagers. I have become a morning exerciser. I find that high-intensity cardio and strength training help prepare me for a busy day and keep me calm and focused.

But some mornings I don't get to work out, and so when I have to change my routine for the afternoon or evening, I will change my workout as well — to yoga or Pilates or walking — something low-intensity that will not require bursts or energy or disrupt my night of sleep.

All of this to say that you need to find your rhythm: the best exercise at the best time of day is the one that you'll get done.

Sleep and Working Out

Most scientists agree that sleep is essential for working out – and for recovery.

According to Exercise + Sleep: The Missing Link to Better Workouts and Faster Recovery, you need a good night's sleep to aid in muscle recovery. If you don't allow proper recovery and muscle repair and then you tax those same muscles groups the next day or two, without that proper repair, you're at greater risk for injury, says Dr. Peter Polos, MD, PhD, FCCP, FAASM, a sleep medicine specialist and sleep expert for Sleep Number.

“You are at risk for a poor performance because you've not had the opportunity to restore to baseline, or maybe even to restore to above baseline, which is the whole point of working out," he says.

Maybe that's why I did so well in the afternoon race.

Poor sleep has an impact on cognition, alertness and reaction time, “all of which are very important to an athlete," he says.

Morning vs. Evening Workouts

Studies show that exercising at different times can have different types of effects. For example, one study following men at high risk for type 2 diabetes who worked out from 8-10 a.m. compared to men who worked out at 3-6 p.m. found that the afternoon group had better results. But that could also be because they ate less or more healthily after working out, the author noted.

Other studies show that morning exercise produces better aerobic results.

But again – that can't be the question.

“Scientific evidence moreover shows that exercise plays a key role in improving health-related physical fitness components and hormone function. Regular exercise training is one of the few strategies that has been strictly adapted in healthy individuals and in athletes," a review of all the time-dependent exercise studies showed, noting that “time-dependent exercise has different outcomes, based on the exercise type, duration, and hormone adaptation."

In other words, maybe scientists can't detect the average perfect time for a specific exercise, but they can find the exact time working out would be best for you ... and your chronotype.

What that means is that if you're not a morning person, if your chronotype shows you're better suited to a later start, then you probably shouldn't exercise first thing in the morning. You might not be well rested, and your reaction time, cognition and alertness — certainly important for sports like tennis, and even biking in public — will be impaired.

Which Exercise — And When

There are too many variables when it comes to exercise: is it high intensity or low intensity? Aerobic or anaerobic? Some are better in the morning, to wake you up and not disrupt going to sleep, and others are better in the afternoon, to lower glucose and belly fat.

There is no one answer about what time of day to exercise because there are too many exercises and people are too different. The important thing is to figure out what works for you.

Read also:

• Why Everyday Athletes Need Sleep For Better Workouts

• Exercise + Sleep: The Missing Link to Better Workouts & Faster Recovery

Like diet and exercise, quality sleep is essential for optimal well-being and performance. Because everyone's sleep needs are different, Sleep Number® smart beds sense your movements and automatically adjust firmness, comfort and support to keep you both sleeping comfortably. Find your Sleep Number® setting for your best possible night's sleep.

ABOUT THE AUTHOR

Amy Klein writes about health, lifestyle and parenting for publications like Business Insider, NBC/Think, Newsweek and others.