When work runs long, the commute home is slow, and cooking dinner takes forever (you promised yourself you’d stop ordering takeout), it’s normal to try to squeeze in a quick workout before crashing. Better than not exercising at all, right? Unfortunately, a recent study has bad news for you: Intense workouts shortly before bedtime may negatively impact your sleep.
After monitoring the exercise, sleep, and heart activity of 14,689 people for a year, an international team of researchers revealed that exercising within four hours of going to sleep is associated with taking longer to fall asleep, sleeping less, poorer sleep quality, along with higher nocturnal resting heart rate and lower nocturnal heart rate variability—both of which are typically linked to health risks.
“Intense exercise in the evening can keep the body in a heightened state of alertness, which is why public health guidelines have previously advised against working out too close to bedtime,” Josh Leota from Monash University’s School of Psychological Sciences said in a university statement.
While some previous studies have challenged these guidelines by suggesting that late workouts don’t always disrupt sleep, Leota claims those studies “relied on small sample sizes and laboratory settings, and rarely involved exercise bouts that elicit substantial cardiometabolic demand on the body,” he added, casting doubt on the validity of their results.
To shed light on the soundness of these public health guidelines, Leota and colleagues conducted a new study, published Tuesday in the journal Nature Communications. The team monitored the 14,689 study participants with multi-sensor biometric devices and gathered four million nights’ worth of data to investigate the potential association between late workouts, exercise intensity, sleep, and heart activity during sleep.
Their analyses of the data accounted for age, gender, season, weekday, fitness levels, and how participants had slept the night before. The results link a late, strenuous workout to the aforementioned signs of impaired sleep health.
“Evening exercise—particularly involving high levels of cardiovascular strain—may disrupt subsequent sleep, resting heart rate, and heart rate variability, thereby impairing a critical stage of the recovery process,” said Elise Facer-Childs, senior author of the study also from Monash University School of Psychological Sciences.
Workouts considered “strenuous” were exercises that caused persistently elevated respiratory rates, heart rate, core body temperature, and mental alertness, like high-intensity interval training, long runs, or football games. So “if exercising within a four-hour window of bedtime, people could choose brief low intensity exercises, such as a light jog or swim, to minimize sleep disruption and allow the body to wind down,” Leota added.
The study ultimately holds important implications for sleep health, shedding light on how late night workouts impact crucial shut-eye and empowering individuals to get the best rest they can.
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