Most people are aware of how exercise can help us sleep. Research has proven it time and time again and, let’s be honest, you have probably felt the benefits yourself, nodding off as soon as your head hits after a long walk or run. But a new study has found that exercising shortly before going to bed could actually be the source of a number of sleep problems for healthy adults.

The research, published in Sleep Medicine Reviews, suggests that doing high-intensity exercise two hours or less before you go to sleep could negatively impact your sleep quality. 

The review suggests that the timing is even more crucial than previously thought when it comes to sleep and exercise, as it also found that exercising more than two hours before sleep helped people fall asleep more quickly and stay asleep for longer.

According to the study, an increased heart rate is one of the reasons participants found it difficult to sleep shortly after high-intensity exercise, as this led to physiological excitement, which they did not recover from until three hours after they had stopped exercising. 

On top of this, the researchers cited fatigue of the central nervous system and changes in body temperature as factors that affect sleep quality after exercise, adding: “In particular, sleep onset may be delayed due to exercise-induced elevation in body temperature.” This is because your body temperature needs to drop slightly in order to facilitate sleep, which could be disrupted if the body temperature is still high due to exercise.

Along with difficulty falling asleep, the study also found that participants who had completed high-intensity exercise two hours before falling asleep woke up several times during the night to urinate, having drank excess water during and after their workouts, which caused sleep disturbance.

If you do prefer to workout in the evening, it’s not all bad news. According to the study, high-intensity exercise completed more than two hours before bedtime may benefit sleep. Plus, a short period of acute high-intensity exercise, as opposed to a full session, shouldn’t have any effect on healthy, young and middle-aged adults without sleep disorders. People with evening chronotypes (aka night owls) were also less affected by working out close to sleep than early birds were.

Your sleep quality also may also be affected by the type of exercise you do in the evening: “[R]elative to a no-exercise condition, an acute evening cycling led to more favorable changes in sleep […] than running which increased REM sleep latency,” researchers write. “Running is more likely to cause exercise-induced muscle damage and inflammation than cycling and hence, may affect sleep.”

Although, they do note that physically fit individuals were less likely to be affected by vigorous exercise and had better sleep outcomes than sedentary individuals.

The conclusion? Try and exercise two hours or more before bedtime if you can, either by heading to the gym straight from the office or fitting your workout in at lunchtime or in the morning. If your schedule is proving too busy and you’re set on a high-intensity workout, make it a quick one and, if possible, a low-impact exercise like cycling for a good night’s sleep.

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