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MELBOURNE, Australia – Working out vigorously too close to bedtime could cost you precious sleep, according to new research led by Monash University. The study, published in Nature Communications, found that strenuous exercise performed four hours or less before hitting the pillow was associated with delayed sleep onset, reduced sleep duration, poorer sleep quality, and disruptions to nighttime heart activity.
This investigation, described as the first and largest of its kind to identify this link, analysed data from an international sample of 14,689 individuals over a year. Using multi-sensor biometric WHOOP Straps, researchers collected exercise, sleep, and cardiovascular data amounting to four million nights’ worth of information.
The collaborative effort between Monash and WHOOP researchers specifically examined how evening exercise timing and intensity (strain) correlated with sleep patterns and nocturnal cardiac metrics like resting heart rate and heart rate variability (HRV).
The findings indicated a clear dose-response relationship: the later the exercise and the higher the strain, the greater the negative impact on sleep. This combination led to individuals taking longer to fall asleep, sleeping for shorter periods, experiencing lower quality sleep, having a higher resting heart rate during the night, and lower HRV. These results held true even after adjusting for variables such as gender, age, day of the week, season, general fitness level, and the quality of the previous night’s sleep.
High-strain exercise, as defined in the study, includes activities that cause sustained increases in breathing rate, core body temperature, heart rate, and mental alertness. Examples given include High-Intensity Interval Training (HIIT), demanding team sports like football or rugby, or undertaking a long run.
Dr. Josh Leota, first author from the Monash University School of Psychological Sciences, noted the historically “puzzling” nature of the exercise-sleep link. “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,” he said. However, he pointed out that smaller, controlled laboratory studies often yielded less conclusive results, potentially due to their limited scale and the lower intensity of exercise involved.
Based on the robust findings from this large-scale, real-world data, Dr. Leota suggests individuals aiming to optimize sleep health might benefit from completing their workouts more than four hours before their intended bedtime. “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,” he advised.
Senior author Dr. Elise Facer-Childs, also from the Monash University School of Psychological Sciences, emphasised the consistency of the findings across all measured outcomes. “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,” she stated.
Dr. Facer-Childs highlighted the significant public health implications, particularly given widespread sleep issues (citing Australian statistics where 2 in 3 adults report sleep problems and 1 in 5 don’t get the recommended 7+ hours). The study offers crucial insights for refining advice on the timing, duration, and intensity of exercise to promote better population sleep health.
Disclaimer: This news article is based on information provided about a specific scientific study published in Nature Communications. It is intended for informational purposes only and does not constitute medical advice. Consult with healthcare or fitness professionals for personalized guidance regarding exercise routines and sleep health.
