Regular exercise remains essential for good health, but new research suggests that the timing of intense workouts can affect sleep quality and nighttime heart activity.
A study involving 14,689 people from different countries found that engaging in high-intensity exercise within four hours before bedtime may delay sleep, keep the heart rate elevated, and leave individuals feeling less rested the following day.
Researchers monitored participants for one year, tracking their exercise habits and sleep patterns. The analysis showed that intense workouts completed at least six hours before bedtime had little negative effect on sleep, and in some cases were associated with longer and better-quality sleep.
However, the closer intense exercise was performed to bedtime, the greater the impact. People who completed intense workouts two hours before sleeping took about 36 minutes longer to fall asleep compared with those who did lighter exercise.
When intense workouts ended less than two hours before bedtime, the delay in falling asleep increased to about 80 minutes.
The research also found that late intense exercise reduced total sleep duration. Workouts completed two hours before bedtime were linked to a 5.4% reduction in sleep time, equivalent to about 22 minutes, while exercising closer to bedtime reduced sleep by nearly 14%, or around 43 minutes.
Sleep quality also declined among people who performed intense workouts close to bedtime, with researchers recording a 5.6% decrease compared with those who engaged in lighter activities.
Scientists explained that intense exercise stimulates the sympathetic nervous system, increasing alertness and keeping the heart active, while the body normally needs to shift into a relaxed state at night to prepare for sleep.
The findings do not suggest stopping exercise but rather adjusting workout schedules. Researchers recommend completing demanding activities such as running, weightlifting, and high-intensity interval training (HIIT) at least six hours before bedtime.
For those who can only exercise in the evening, lighter activities such as walking, yoga, or stretching may be better alternatives that are less likely to interfere with sleep.
