Have you ever finished a late-night workout and been too wired to fall asleep? On several occasions, I’ve experienced firsthand the negative impact that a nighttime competition or hard workout can have on my own sleep. Maybe it’s due to the excitement of a good game or the thrill of a personal best performance that inhibits sleep, or perhaps the elevated adrenaline levels are to blame. In any case, heavy exertion close to bedtime seems, at least on the surface, not to be ideal for sleep.

This seems counterintuitive. Shouldn’t exercise and all of the energy it burns actually leave us feeling fatigued and ready for bed?

This is true, at least for regular exercise. People who consistently engage in exercise, no matter the type or intensity, report that they sleep better and experience far fewer symptoms of insomnia and disturbed sleep compared to people who don’t exercise. Exercise reduces the time you need to fall asleep, decreases the number of times you wake up each night, and increases the amount of time you’re asleep.

For proper sleep, being a couch potato is the worst thing you can do, and exercise one of the best.

It’s also well-known that just one session of exercise — whether that be a sweaty endurance run or heavy resistance training session — helps you sleep longer and deeper. Even just 30 minutes of weight lifting enhances your sleep, although it does seem like exercise over 1 hour long may improve sleep more than shorter sessions.

How and why does exercise improve sleep? The explanations are nearly endless and involve exercise’s beneficial effects on body composition, glucose regulation, immune function, cardiovascular health, and mood. All of these health improvements have a direct impact on sleep quality. However, exercise also directly affects our nervous system and our circadian rhythms in a way that also improves how well we sleep. Then there’s also the fact that exercise does deplete energy and increase physical fatigue — making sleep feel all that much better.

Hopefully, you are now convinced that not only is a regular exercise routine one of the best ways to improve your health, but it’s non-negotiable if you want to achieve the best sleep possible. As we will find out in a bit, our biological rhythms depend on a regular habit of physical activity.

But now the question becomes, when should you exercise to achieve the best sleep? The timing of exercise during the day — whether you choose to work out in the morning, afternoon, or evening — can have a profound effect on your sleep. Time is a variable that we can manipulate to achieve the goal of better sleep through exercise, as long as we do it correctly.

Exercise and circadian rhythms

You’ve probably heard of circadian rhythms — our body’s ~24-hour cycles that regulate our metabolic function, our athletic performance, and, relevant to our discussion, our sleep-wake cycles.

Sleepiness and wakefulness are moderated in large part by the “sleep hormone” melatonin. Melatonin release follows its own rhythm — rising at night to promote sleep and then falling toward the morning when we begin to wake up. Proper melatonin rhythms at the right time of day ensure we achieve the best sleep possible and are alert and awake during the day.

Where does exercise come into play? Well, light is the primary synchronizer of our circadian rhythms, and morning light exposure is crucial for signaling to our body the time of day and regulating melatonin production, among other hormones. Exercise is another strong “time giver” to our circadian system. It’s an environmental cue that can also help keep our body’s rhythms in check.

When we exercise in the morning or early afternoon, this helps to shift our circadian rhythm of melatonin earlier in the day — what is known as a phase advance — and promotes an earlier peak in melatonin production. The best time to exercise for this effect seems to be at 7 am or between 1 and 4 pm — and even better if paired with outdoor natural light exposure.

Being active is crucial for the proper alignment of our circadian rhythms and, in relation, proper sleep.

But what time of day produces the most beneficial effects for sleep? Should you exercise in the morning, afternoon, or evening?

Does nighttime exercise hurt your sleep?

It was once recommended that people should avoid exercising too close to bedtime due to the fear that it would impair sleep. Exercise elevates heart rate and body temperature, increases arousal, and leads to the production of endorphins and hormones like adrenaline and noradrenaline — all of which are counterproductive to achieving quality sleep.

For this reason, a lot of research has been done to investigate whether late-night exercise really is harmful to sleep. There seems to be a consensus that if you do low to moderate intensity exercise in the evening, your sleep might not suffer, as long as you finish at least 90 minutes before hopping into bed.

Maybe you’re competing or running a race that ends late at night. Will that affect your sleep? It appears that, like moderate intensity exercise, high-intensity exercise may not harm sleep, but you’ll need to finish 2-4 hours before bed to avoid any disruption.

So, rather than the intensity, the timeline of exercise in relation to your bedtime seems to matter, and this is because you need enough time for body temperature to come down, heart rate to fall to resting levels, and arousal to dampen a bit before your body can fall asleep. The more intense or strenuous the exercise, the more time you’ll need to allow between the activity and bedtime, although there may be ways to expedite the process like taking a cold shower or bath to bring down your core body temperature.

One final thing to note is that, while a lot of evidence shows that late-night exercise may not impair sleep, there doesn’t seem to be a lot of support that it will improve sleep either.

Morning exercise and sleep

From a biological perspective, morning exercise would seem to be the best option for improving sleep. We are hard-wired to engage in activity during the early morning and the day, aligning with our 24-hour rhythmic peaks in many physiological processes like metabolism and alertness.

Compared to evening exercise, morning exercise enhances melatonin secretion at night and thus is more likely to be sleep-promoting. Evening exercise can actually delay melatonin secretion the next day, favoring a later bedtime (or at least making it harder to fall asleep at your usual bedtime). While a one-off occasion might not throw off your entire sleep schedule, it’s good to be aware of these effects.

Morning exercise also has more of an effect on the parasympathetic (“rest and digest”) nervous system during sleep and even increases measures like heart rate variability at night. On the other hand, late-night exercise can activate the sympathetic nervous system, which could perhaps reduce your chances of achieving restful sleep after being in the “fight and flight” state so close to bed.

There haven’t been a lot of comparisons of morning and evening exercise regarding sleep. Some studies find that regular morning aerobic exercise improves sleep quality, and people who report exercising in the morning have been shown to have improved sleep quality, longer sleep duration, and more restful sleep compared to late-night exercisers.

There is also some support for the idea that lower-intensity exercise in the evening can improve sleep quality and sleep satisfaction in older adults.

If we look at a majority of the evidence out there, it seems that for the most part, there aren’t major differences between morning exercise and evening exercise when it comes to effects on sleep. But there is a final — and perhaps most important — factor to consider when thinking about when to time your exercise for sleep. Personal preference.

Early birds and night owls

The best answer to “when should I exercise” might be: “whenever you prefer to exercise.”

This isn’t just about personal preference, but about our biological inclinations toward morning and evening — something known as our chronotype.

Your chronotype is responsible for how awake and alert you feel (or don’t feel) at certain times of the day. Generally, we talk about chronotype in terms of people being an “early bird” or a “night owl.” Early birds tend to wake up early, be most productive at the beginning of the day and have a hard time staying up late. Night owls are the opposite — late risers who have trouble waking up early, and they tend to do some of their most productive work and socializing in the late afternoon and evening.

Your chronotype probably determines when you choose to exercise. Unless constrained by work, family life, or other obligations, early birds well tend to enjoy working out in the morning, and night owls will lean toward afternoon and evening exercise.

The effects of exercise on sleep probably depend not only on when you exercise but on your chronotype as well. Earlier chronotypes who are forced to exercise late at night are at risk of experiencing disruptions in sleep quality. In other words, if you’re used to exercising in the morning and switch up your routine, sleep may take a hit.

This doesn’t seem to apply in the opposite direction. Late chronotypes who work out in the morning don’t experience the same sleep disruptions that come from this change of schedule.

When left to choose the time of exercise — assuming that individuals will self-select their exercise time based on chronotype — the intensity of exercise and time of day don’t seem to make a difference in sleep quality. This is an important finding to underscore! It seems that if we exercise when we naturally prefer, there won’t be any negative effects on sleep, only positive. Align your practices with your preferences.

What if you are an early morning exerciser who is forced into a late-night workout? Research shows that taking 10 mg of melatonin after your workout can improve sleep quality and help you sleep for longer. But best to not make this a habit, since long-term melatonin use could disrupt your natural melatonin production.

Your action plan for better sleep

Ready to start optimizing your exercise timing for better sleep? Here are some simple action items, based on science, to help you perfect your daily routine.

• For light- and moderate-intensity exercise of 30 minutes to an hour or more, finish exercise at least 90 minutes before bed to allow body temperature, heart rate, and sympathetic activity to return to baseline levels
• For high-intensity exercise or competition, allow at least 2-4 hours between the end of exercise and bedtime
• If you’re an early chronotype, exercising in the morning will help maintain your circadian rhythms and sleep schedule
• Early chronotypes who exercise late at night should take 10 mg of melatonin after their workout to help reduce the negative effects of exercise on sleep
• Late chronotypes can workout in the morning without any negative effects on sleep
• Our personal preferences about when to exercise seem to align well with our natural chronotypes. A consistent exercise routine at the same time of day — regardless of whether it’s in the morning or at night — is essential to a healthy sleep-wake schedule
• Any exercise, regardless of the time of day, is better than no exercise at all. The worst sleepers tend to be people who never exercise.

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