Individuals often have personal preferences regarding when to exercise, whether it involves starting their day with a workout or choosing to unwind by visiting the gym after work. Engaging in regular exercise brings numerous health benefits, such as reducing the risk of colorectal cancer and potentially extending one’s lifespan. Achieving the recommended 150 minutes of physical activity each week can also lower the risk of more than 200 diseases.
However, those who choose to exercise later in the day might be impacting another vital aspect of health: sleep quality. According to Elise Facer-Childs, the lead author of a new study published on April 15 in Nature Communications, evening exercise—especially activities with high cardiovascular intensity—might disrupt sleep, resting heart rate, and heart rate variability, thus affecting the recovery process.
Researchers from Monash University in Melbourne, Australia, observed that exercising within four hours of bedtime was associated with later sleep onset, reduced sleep quality, a higher resting heart rate, and lower heart rate variability, which is the variation in time intervals between heartbeats. These effects were notably significant for high-intensity workouts conducted during the evening, such as high-intensity interval training (HIIT), soccer, or long-distance running.
The study gathered data from an international cohort consisting of 14,689 participants monitored over one year, resulting in four million recorded nights of data. Participants wore a WHOOP Strap fitness monitor to track their exercise, sleep, and cardiovascular information.
Previous research has demonstrated that exercise enhances sleep quality and may even help address sleep disorders like insomnia. A study from earlier this year indicated that exercise increases melatonin production, a hormone essential for regulating sleep cycles, and could help individuals fall asleep faster.
While some studies have claimed that evening exercise does not interfere with sleep, the authors of this study suggest that prior findings were less decisive. Co-author Josh Leota explained that those studies often relied on small sample sizes and laboratory settings, rarely involving exercise that places significant cardiometabolic demand on the body, which raises questions about the applicability of such findings.
According to Leota, high-intensity evening workouts can keep the body in an alert state, a reason public health guidelines have previously advised against exercising too close to bedtime. Sleep is crucial for recovery, not just for subsequent workouts but also to minimize injury risk and enhance exercise performance. Research shows that poor sleep quality can negatively affect muscle strength and endurance, increase injury risk, and hinder injury recovery.
Additionally, inferior sleep is linked with accelerated brain aging, reduced cognitive functioning, compromised mental health, and a weakened immune system. Researchers noticed that people who exercised close to bedtime had lower heart rate variability, associated with a shorter lifespan, obesity, cardiovascular disease, inflammation, poor mental health, and diminished immune health. They also observed that evening exercisers had a higher resting heart rate, indicating less efficient heart function. A high resting heart rate is connected with higher body weight, elevated blood pressure, and lower physical fitness, according to the American Heart Association.
Leota suggested that those aiming to improve sleep health might benefit from exercising at least four hours before bedtime. Alternatively, engaging in brief, low-intensity exercises such as a light jog or swim could help minimize sleep disruptions and allow the body to relax.
For additional fitness insights:
- Understand your VO2 max, a crucial health metric for assessing fitness.
- Learn four strategies for maintaining workout habits year-round.
- Discover why excessive sitting poses health risks that exercise cannot counteract, along with five tips to increase physical activity.
- Determine the right amount of protein intake based on your workout routine.
This article was initially published on Fortune.com.
