As a general rule, regular running promotes better sleep. But there appears to be an exception: hard exercise in the hours before bedtime.
That’s the conclusion of a new study in the journal Nature Communications. Looking at the sleep data of 14,000 WHOOP users, researchers investigated how timing and intensity of evening exercise affect sleep and recovery.
They found that both intense or long workouts within four hours of bedtime had a detrimental impact on sleep onset (when you go to sleep) quantity (how long you sleep) and quantity (how well you sleep).
Exercise 6+ hours before bedtimeSleep onset
Six or more hours before ‘habitual sleep onset’ (i.e. the time you naturally nod-off), you can essentially exercise however you wish. In fact, high- and maximal-strain exercise – think high-intensity intervals or a two-hour long run – promoted marginally earlier sleep (by about 2-6 minutes).
Sleep quantity
All exercise intensities during this time window improved sleep duration. The higher the strain the better – you’ll get an extra seven minutes off the back of a maximal-strain session.
Sleep quality
Surprisingly, sleep quality suffers during this window, regardless of the intensity or duration of the exercise
Exercise 4-6 hours before bedtime Sleep onset
Only light exercise – think a slow jog – had a sleep-promoting effect. Everything else (moderate, high and maximal workouts) was essentially neutral. In other words, they didn’t affect sleep negatively or positively.
Sleep quantity
Slightly negative impact on sleep quantity, with harder exercise having the biggest impact.
Sleep quality
Suffers, regardless of exercise intensity or duration
Exercise 2-4 hours before bedtimeSleep onset
During this window, any type of exercise was associated with a later sleep onset. Specifically, moderate-to-maximal exercise four hours before bedtime delayed sleep onset by 8-20 minutes.
Sleep quantity
Exercise conducted within four hours of bedtime had a negative effect on sleep duration – contributing to around a nine-minute reduction.
Sleep quality
Surprisingly, light exercise in this window actually marginally improved sleep quality. All other categories of exercise – from moderate to maximal – had the opposite effect.
Exercise 0-2 hours before bedtimeSleep onset
This is where things get more serious. Moderate-to-maximal intensity exercise within two hours of bedtime delays sleep by a fairly significant 11-36 minutes.
Sleep duration
Expect a 30-minute reduction in sleep quantity. As with sleep onset, the effects are dose-dependent: the closer you exercise to bedtime and the higher the exercise strain, the less you’ll sleep that night.
Sleep quality
Not impacted by light exercise (i.e. a slow jog), but negatively impacted by intensities higher than this.
What can you do about it?
If you do find yourself running hard in the evening – say, during a Tuesday night track session –find a way to bring your core temperature down: it’s probably the biggest factor affecting your sleep post-exercise. A cold shower or bath are two practical options.
More generally, if you’re someone who prefers to run after work, it’s worth considering either lowering the duration or intensity of the effort. And if you’re one of those dedicated types who runs twice a day, do the harder run in the morning.
Finally, it’s worth noting that the sleep-reducing effects of exercise are fairly minor – often less than 10 minutes – a price many of us will view worth paying for an evening run.
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