When to exercise matters

Your body clock may shape how much you get from exercise: a new trial found bigger gains when workout time matched whether people were morning or evening types. (openheart.bmj.com) The 12-week randomized trial, published in *Open Heart* in April 2026, enrolled 150 sedentary adults ages 40 to 60 in Lahore, Pakistan, all with at least one cardiovascular risk factor. Researchers classified participants as morning or evening types with the Morningness-Eveningness Questionnaire and 48-hour core body temperature monitoring. (openheart.bmj.com) Everyone followed the same supervised program three times a week; the variable was timing. One group exercised in sync with chronotype, while the other trained at the opposite time of day. (openheart.bmj.com) Chronotype is a person’s built-in preference for earlier or later sleep and activity, often described as “early bird” or “night owl.” The American Heart Association said in an October 2025 scientific statement that circadian disruption is linked with obesity, Type 2 diabetes, high blood pressure and cardiovascular disease. (newsroom.heart.org) In the trial, the chronotype-matched group posted larger improvements in systolic and diastolic blood pressure, heart-rate variability, peak oxygen uptake, low-density lipoprotein cholesterol, fasting glucose and sleep quality than the mismatched group. The authors said the findings support adding chronotype to exercise prescriptions for people at cardiovascular risk. (openheart.bmj.com) That does not mean a universal “best hour” exists for everyone. A 2024 commentary in the *Journal of Human Hypertension* said the evidence points toward outcome-specific effects and argued that advising people to exercise when they can remains reasonable, especially when work schedules limit choice. (nature.com) Researchers have been moving away from one-size-fits-all timing advice for several years. A 2022 review on “chrono-exercise” described how circadian rhythms affect body temperature, hormone release, metabolism and physical performance across the day. (sciencedirect.com) The newer blood-pressure work also suggests timing changes physiology, not just convenience. A study in *Sleep* published in February 2026 found the body’s internal circadian system modulates blood-pressure responses after exercise in healthy adults. (academic.oup.com) The practical takeaway from the evidence so far is narrower than the headlines: if you have flexibility, matching workouts to the time you naturally feel most alert may improve sleep and some cardiometabolic measures. If you do not, the older advice still stands — regular exercise beats perfectly timed exercise you never do. (openheart.bmj.com; nature.com)