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Why Knowing Your Sleep Chronotype Is a Fitness Game-Changer

Understanding when and why you feel most energized can drastically improve your workouts.

By Michelle KonstantinovskyFebruary 29, 2024


There was a time in my life when I really, truly tried everything in my power to be an evening exerciser. After months of misery, half-heartedly and exhaustedly logging miles and taking fitness classes, I had to reevaluate. And what I eventually realized is that once the sun goes down, my body seems to enter shut-down mode. After I experimented with switching my workouts to the a.m., my suspicions were confirmed: I am actually, astonishingly, more of a morning person. 

While there’s definitely no right or wrong way or time to move your body, there may be an advantage to understanding when and why you feel most energized. That’s something called your “sleep chronotype” and knowing yours could be a fitness game-changer. Here’s how.

What Are Sleep Chronotypes?

While I’ve heard (and written) plenty about sleep and circadian rhythms (i.e. the physical, mental, and behavioral changes you experience in a 24-hour period), I’ve found chronotypes to be more of an under-the-radar and underrated topic. Simply put, your chronotype (sometimes referred to as “diurnal preference”) describes your personal, unique, and preferred timing when it comes to sleeping and waking. While chronotypes are usually determined through self-reported questionnaires, they’re thought to be associated with a variety of real, physiological differences in measures like body temperature and hormone secretion rhythms.

“A chronotype is a way to characterize the general way your internal clock behaves,” says Michael A. Grandner, PhD MTR DBSM, director of both the Sleep and Health Research Program at the University of Arizona and Banner-University Medical Center’s Behavioral Sleep Medicine Clinic, and an associate professor of psychiatry at the UA College of Medicine. “It’s a concept that was originally developed in the 1970s in order to refer to a construct that represents how your body organizes itself across 24 hours.” 

You’ve probably heard the terms “early bird” and “night owl.” Those descriptors are more than cute labels; they actually describe the two main types of chronotypes. As Grandner puts it, people who have a relatively late rhythm (i.e. they prefer to go to bed late and wake late, and have other body rhythms that tend to occur later) are the "night owls” and those who function optimally on an earlier schedule are the “early birds” (or “morning larks,” depending on who you ask). 

“I would consider sleep chronotype as your sleep personality,” says triple-board-certified sleep medicine physician and founder of Restful Sleep MD, Funke Afolabi-Brown, MD. “It’s your natural tendency for when you are likely to fall asleep and when you are likely to wake up.”

Chronotype vs. Circadian Rhythm

While you may already be formulating your hypothesis about whether you fall into the early or late camp, you may also be wondering how sleep chronotypes differ from circadian rhythms, which seem to get a lot more attention. The answer is: they don’t, exactly. Chronotypes are actually considered an “expression of individual circadian rhythmicity, which is related to sleep, diet, and physical activity patterns, including exercise.” 

“A person's circadian rhythms are the many rhythms in their biology that fluctuate at about 24 hours, including everything from sleep-wake rhythms to rhythms in the brain, heart, liver, and many other systems,” Grandner says. “Chronotypes are a way to describe where in the 24 hours those rhythms tend to cluster.”

So while your circadian rhythm describes your body’s overarching time keeper that dictates a variety of physiological functions in addition to sleep (like mood, cognition, temperature, etc.), your chronotype speaks more specifically to the time of day all your major functions tend to occur.

“A person’s circadian rhythm is their body’s internal clock responsible for regulating various processes in the body including their sleep-wake cycle,” Brown says. “The circadian rhythms influence our chronotype but also influences other systems; chronotypes mainly are about when we are more likely to fall asleep and wake up.”

What Are the Different Types of Sleep Chronotypes?

Neurologist, sleep specialist, author, and podcast host Chris Winter, MD, says you can think of your chronotype as a way to describe a specific part of your overall circadian rhythm. “Chronotype refers to the relative timing...of your circadian rhythm,” he says. “Later timing is known as ‘delayed’ and earlier timing is called ‘advanced.’ Chronotype is more of a description of a circadian rhythm—a characteristic.” So in addition to self-identifying as a night owl or early bird, you can also consider your chronotype to be “delayed” (aka a night owl) or “advanced” (aka an early bird). 

But if you’ve done any Googling around your sleep chronotype, you may have encountered many more colorful categories in the chronotype discussion. “The two broad sleep chronotypes include morning types (larks) and evening types (owls) and there’s also an intermediate group,” Brown says. “But Micheal Breus, a world-renowned sleep expert, categorized the different chronotypes into ‘Bear,’ ‘Lion,’ ‘Dolphin,’ and ‘Wolf’ as a fun and easy way to help people understand their sleep tendencies. These categories are a bit nuanced as they tend to overlap and are not as concrete as they are depicted.”

According to Breus, the old-school chronotype categories aren’t sufficient to describe the intricacies of individual sleep drives. Rather than putting patients in the lark, owl, or intermediate bucket, he assigns them one of four wild animal labels. Lions are the super early risers who tend to sleep pretty well and have a natural inclination for routine and moderation. Bears are “go-with-the-flow” types who are most alert and productive in the middle of the day, from late morning through early afternoon. Wolves are the ones who are classic nighttime enthusiasts, preferring to snooze late and hit their stride in the wee hours. And Dolphins are the people that tend toward a “wired and tired” state, meaning they’re chronically fatigued during the day and feel restless with nervous energy at night.

If those categories resonate more with you, feel free to label yourself a Lion, Bear, Wolf, or Dolphin, accordingly. But if you don’t see your own chronotype reflected accurately here, it’s totally fine to stick with the owl and lark analogy. 

Woman struggling to fall asleep

fcafotodigital / E+ via Getty Images

What Determines Sleep Chronotype—and Can You Change It?

Like so many of our physical and psychological functions and behaviors, sleep chronotype is thought to be determined through a combination of genetics and environment. That means that while we may be predisposed to being early, late, or intermediate types, how we’re raised, as well as what we do in our day-to-day lives, may have an impact on when (or even if) certain genes are expressed. 

“Genetics may play a role in determining our chronotypes,” Brown says. “As a result of these genetic influences, people are likely to be morning persons, evening persons, or somewhere in between. There are many other factors that play a role like environmental, habits, and lifestyle factors. Also these tendencies tend to change as we age.”

Getting older is just one way your chronotype may shift over time, according to Winter. “Chronotypes are a manifestation of the nature of a series of genes that affect circadian timing,” he says. “We can become more morning-oriented—ask any Naval Academy student/midshipman—but whether we are changing things on a genetic level is hard to say. I would guess our actions are influencing genetic expression.”

So while your genetic predisposition to be an early, late, or intermediate chronotype is pretty set, your habits and circumstances definitely can swing the sleep pendulum. “Many people can shift their own internal rhythms to become more of an ‘early’ or ‘late’ person based on activity, light, sleep, and other patterns,” Grandner says. “For example, regularly waking up early, getting light early in the morning, getting movement in the morning, and avoiding these things later at night, can make you more of an ‘early’ person.”

Did you catch that? If you’re desperately wishing to be more of an early bird, pressing play on a Peloton class first thing in the morning may actually help you start to move toward lark territory. Of course, the desire to want to change your routine is a big contributor in your success in shifting it; my attempt to be an evening exercise never truly stuck because I didn’t need or feel compelled to turn my day upside down. I was able to find an alternative schedule that fit better with my natural chronotype. But if you want to (or have to) move your workouts and obligations to an earlier or later time, you can gradually do so by implementing daily habits that encourage the shift. 

“While you may not be able to change your chronotype—it’s hard wired—you can influence it with certain behavioral and environmental factors,” Brown says. “For instance, timing of our exposure to light, meals, and physical activity can cause gradual shifts in our circadian rhythms and influence our chronotypes.”

Why Is Knowing Your Sleep Chronotype Important?

When you start to take note of your natural tendencies toward early or late chronotype patterns, you can actually empower yourself with information to optimize your lifestyle. Not only can understanding your chronotype help you take advantage of your natural energy spikes, but it can help inform your choices around work responsibilities, social obligations, and more.

“If you know you’re more of a late person, perhaps it is unwise to schedule important activities early in the morning,” Grandner says. “And if you're more of a morning person, it may be a bad idea to try to be productive at night.”

Brown says that by getting to know your patterns, you can start planning out your days to maximize your energetic bursts. “Based on your chronotype, there are specific times when we are more likely to be cognitively and physically productive,” she says. “Knowing your chronotype can help you determine when best to eat, exercise, and do more mentally tasking work, for instance, which will boost your overall wellbeing.”

How Your Chronotype Can Influence Your Fitness Journey 

Of course, all this talk of optimizing your lifestyle to improve your overall health probably has you wondering how your chronotype can influence your fitness journey. If you have the privilege of setting your own schedule or the freedom to choose when to work out, knowledge about your chronotype can make a major difference in your physical output and your psychological enjoyment of your exercise time. 

“Knowing your sleep chronotype can help you tailor your fitness routines in a way that optimizes efficiency,” Brown says. “For instance as a morning person, it would be more beneficial to work out earlier in the day when energy peaks. Night owls on the other hand may find that afternoon or evening workouts might be more effective for owls, as their alertness and strength tend to peak later.”

Not only can knowing your chronotype help you feel more excited and enthusiastic about your workout, but it can actually keep you safer. “People who exercise in a way that is aligned with their chronotype may have more benefits and fewer injuries,” Grandner says. According to one study, the evidence is clear that early chronotypes perform best earlier in the day compared to late, and the opposite is true for late chronotypes who have significantly more daytime sleepiness and “perform worse in the morning across all cognitive and physical measures.”

To that end, Winter recommends anyone preparing for a fitness-related event to time their training sessions to align with the timing of the actual race or competition. “Training for an Ironman that begins at 6 a.m. by working out after work is bound to be a rude awakening,” he says.

The Takeaway

It’s important to listen to your body. Everyone has their own specific, unique needs and preferences when it comes to sleep, nutrition, and yes, fitness. Taking stock of your body’s natural patterns and the times of day you feel like your best, most energized self can help you make small changes to optimize your success on the Peloton Bike, Tread, mat, and everywhere else in your life. By tuning into your typical habits and experimenting with the timing of your activities, you can use your sleep chronotype to your advantage and really kick things up a notch in your workouts and beyond.

This content is for informational and educational purposes only and does not constitute individualized advice. It is not intended to replace professional medical evaluation, diagnosis, or treatment. Seek the advice of your physician for questions you may have regarding your health or a medical condition. If you are having a medical emergency, call your physician or 911 immediately.


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