High-Intensity Evening Exercise Cuts Sleep by 43 Minutes

According to a new study, high-intensity exercise performed close to bedtime can significantly disrupt sleep quality and slow overnight recovery. The study analyzed data from nearly 15,000 physically active adults over a year and measured the impact of various levels of workouts close to bedtime. Researchers recommend completing high-intensity exercise at least four hours before sleep onset to optimize sleep quality.

Night owls who hit the gym hard might be losing more than just sweat—your sleep could be taking a hit, too, according to a new international study. Researchers found that high-intensity exercise performed close to bedtime can significantly disrupt sleep quality, and slow overnight recovery. The findings suggest that people seeking better sleep health should avoid strenuous workouts within four hours of going to bed, or opt for lighter exercise during that window.

Scientists and health advocates have long emphasized that sleep is essential for cognitive function, immune system health, emotional well-being, and physical recovery, making it a vital component of overall health. To explore the effects of exercise timing and intensity, researchers analyzed sleep and exercise data from 14,689 physically active adults over the course of a year, using wearable biometric devices. The study focused on how the timing and intensity, referred to in the study as "exercise strain"—a measure of total physical exertion during a workout—affected the results.

“Public health guidelines recommend exercise as a key lifestyle intervention for promoting and maintaining healthy sleep function and reducing disease risk. However, strenuous evening exercise may disrupt sleep due to heightened sympathetic arousal.” Sympathetic arousal is the state in which the body remains alert and physiologically activated, making it harder to wind down for rest. “To optimize sleep, individuals should aim to complete bouts of exercise four or more hours before their sleep onset to minimize potential adverse consequences to their sleep,” the researchers wrote.

When exercise ended two hours before habitual sleep time, participants who engaged in maximal strain workouts fell asleep an average of 36 minutes later, and slept 22 minutes less than those who performed light exercises. The disruptions were even more pronounced when exercise extended past a person’s usual bedtime, with sleep duration cut by up to 43 minutes. The study also challenged traditional sleep health guidelines, which have typically discouraged exercising in the evening. “Contrary to previous sleep health guidelines that discourage exercise at night, recent guidelines are less conservative, suggesting, for example, that moderate-intensity exercise ending at least 90 minutes before bedtime will not delay or disrupt sleep. However, these guidelines do not mention the duration of permissible moderate-intensity evening exercise; a critical consideration when quantifying exercise strain.”