How Bad Is It Really To Work Out At Night?

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For me, the hardest part about working out is finding the time to actually do it. I’m decidedly not an early riser. I’m not even someone who gets out of bed when her alarm goes off. Instead, I prefer a slow morning where I hit snooze, scroll social media, and leisurely make my way to the kitchen to have breakfast. As you can imagine, my mornings aren’t quite conducive to getting out the door and going on a run or heading to the gym.

Really, my only option is to work out at night—but it’s a controversial choice. Sure, there’s something about waiting until basically the last possible second to finally cross a workout off your list that’s stressful, but for me it’s also a way to end my day on a high note. Still, I’m envious of the morning exercisers who preach the benefits of AM activity and wonder if my PM habits have any effect on my sleep, which is the biggest reason people try to avoid an evening sweat session.

And, while I don’t really see myself changing anytime soon, I’d like to at least know: how bad is it really to work out at night? Here’s what experts say.

Meet the experts: Jingyi Qian, PhD, is a sleep scientist at Mass General Brigham and associate director of the Medical Chronobiology Program, Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital. Josh Leota, PhD, is a sleep and circadian scientist and researcher at Monash University, Brigham Women’s Hospital, and WHOOP.

How Evening Workouts Affect Your Sleep

The idea that working out in the evening can affect your sleep isn’t totally out-there. When you’re exercising, you’re activating your sympathetic nervous system (a.k.a. your “fight or flight” response) and raising your core body temperature—both of which can have a negative effect on sleep, says Jingyi Qian, PhD, a sleep scientist at Mass General Brigham. When you work out, your heart rate gets elevated and your respiratory system works harder, which are two things you want to slow before rest. Plus, other environmental factors related to exercise (like bright lights, loud noises, and sports drinks that contain caffeine) can all have an effect on winding down, she says.

That doesn’t mean all hope is lost, though. In fact, the research is mixed about just how bad working out at night is for your sleep. Multiple meta-analyses have concluded that evening exercise doesn’t impact sleep quality, with some researchers arguing for change on public health guidance.

But, if you’ve ever had a long night following a later-than-usual Barry’s class, you might not be so convinced. That’s because, according to new research, there are certain caveats when it comes to exercise timing and sleep. “It really comes down to when and how hard you exercise,” says Josh Leota, PhD, a sleep and circadian scientist at Monash University in Australia. Per Leota’s recent study in Nature Communications, strenuous exercise done too close to bedtime can impact your sleep, but it has to be in that sweet spot of both too intense and too late for it to matter.

Basically, the more demanding the workout, the longer you’re going to need before trying to get to sleep. “The harder you work out, the more activated your body becomes and your nervous system is in a more alert, amped up state,” Leota says. “Your body will recover from that, but the key point is that the time it takes to settle back down is proportional to how hard the workout was.”

Light to moderate activities like a 30-minute jog shouldn’t affect you if finished within 1-2 hours before bed, Leota says. On the other hand, an all-out maximum effort within two hours of bedtime is associated with a 36-minute later sleep onset and 22-minute shorter sleep duration, per Leota’s research.

So, what does this mean for your nightly workouts?

First and foremost, if you’re a nighttime exerciser and you’re not feeling an effect on your sleep, it’s okay to stick with it. There’s no reason to change if you’re not experiencing a problem, Qian says.

But if you suspect your sleep is getting interrupted or you’re an AM exerciser that needs to switch it up on occasion, make sure it wraps up an appropriate amount of time before heading to bed, consider opting for lower intensity exercises, and be mindful of duration. Ultimately, you want to think about strain, Leota says. A short super intense workout will strain the body, but so will a long light to moderate workout.

As a rule of thumb, lighter exercise (exercise where your heart rate stays low like walking, yoga, stretching, or mobility work) can be wrapped up about 2 hours before bedtime, while more intense exercises (like a HIIT class or a speed run) should be done at least four hours beforehand. Something like strength training, depending on how intensely you’re doing it, could fall somewhere in between.

The best thing to do is pay attention to how you feel during a workout and how long it takes you to wind down afterwards. “It doesn’t hurt to run a self-experiment,” Qian says. It might take a few nights of trial and error, but you can determine how much recovery time you personally need before your head hits the pillow.

Before you stress out about your 8pm gym routine, remember: overall, exercise is good for sleep. When you do it might slightly affect the duration and how long it takes you to fall asleep, but general exercise helps build sleep pressure (which is really just another word for sleepiness), improves mood, strengthens circadian rhythms, and promotes the parasympathetic nervous system, Leota says.

You just may want to save the more strenuous stuff for earlier in the day. And, if the best you can do is an evening workout, you don’t need to stop now. “If you can exercise, do it,” Qian says. “In general, physical activity is good for you and most of the people have too little rather than have too much, so if evening is the only time that people can find to do some exercise, I would recommend people do it.”