In brief
- 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 from the United States, Australia, and Switzerland found that high-intensity exercise performed close to bedtime can significantly disrupt sleep quality, and slow overnight recovery. The findings, published Tuesday in Nature Communications, 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.
“Nothing is more important to me than sleep,” biohacker Bryan Johnson previously told Decrypt. “I plan when I eat, my social events, my work schedule, everything around sleep, which is exactly the exact opposite of what society does right now.”
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 developed by the performance tracking company Whoop. 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,” the study said. “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.
Will Ahmed, the CEO of Whoop, emphasized the importance of timing in training on X (formerly Twitter). “If you’re training hard but not sleeping well, when you work out may matter just as much as how you work out,” he 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.
According to the study, 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,” the researchers wrote. “However, these guidelines do not mention the duration of permissible moderate-intensity evening exercise; a critical consideration when quantifying exercise strain.”
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