Study: exercise timing halves gains
- An Open Heart trial found middle-aged adults at cardiometabolic risk improved more when aerobic workouts matched their chronotype than when sessions were mistimed. - In Lahore, 150 adults trained for 12 weeks; systolic blood pressure fell 10.8 mm Hg in the matched group versus 5.5 mm Hg mismatched. - Experts said the trial was short and limited to one at-risk population, though both groups still improved (sciencemediacentre.org)
Your body clock is a built-in timing system that shifts alertness, sleepiness, temperature and hormone release across the day. A randomized trial published April 14 found exercise worked better when workouts matched that clock. (openheart.bmj.com) The study tested chronotype, the tendency to feel sharper earlier or later in the day. Researchers in Lahore, Pakistan sorted 150 sedentary adults ages 40 to 60 into morning-type or evening-type groups. (openheart.bmj.com) All participants had at least one cardiovascular risk factor, such as elevated blood pressure or other metabolic risk. The trial ran from January through June 2025 and used the Morningness-Eveningness Questionnaire plus 48-hour temperature monitoring to classify people. (openheart.bmj.com) Researchers then assigned participants to exercise either at their preferred time or at the opposite time. Both groups did the same supervised program: moderate-intensity aerobic training, five sessions a week, 40 minutes a session, for 12 weeks. (openheart.bmj.com) Of the 150 enrolled, 134 finished the program. The chronotype-aligned group posted larger gains across blood pressure, heart-rate variability, peak oxygen uptake, low-density lipoprotein cholesterol, fasting glucose and sleep-quality scores. (openheart.bmj.com) The clearest number was systolic blood pressure: it fell 10.8 mm Hg in the matched group and 5.5 mm Hg in the mismatched group. That is where the “nearly half the benefit” framing comes from, though the paper measured several outcomes, not one single fitness score. (openheart.bmj.com) The paper did not say morning workouts are best for everyone. It reported that early chronotypes did better with morning exercise, while late chronotypes did better with evening sessions. (openheart.bmj.com) Outside experts said the design was stronger than much of the older timing literature because the trial was randomized and the training was supervised. They also said the sample was moderate in size, the intervention lasted only 12 weeks, and the findings came from one at-risk population in Pakistan. (sciencemediacentre.org) Those experts also cautioned against overselling the result. The chronotype measure relied mainly on a questionnaire, and the misaligned group still improved, which leaves the basic advice unchanged: exercise helps even when the schedule is not perfect. (sciencemediacentre.org) A separate 2024 cohort study in JAMA Network Open points to another part of the picture: people who mostly sat at work had a 16% higher risk of death from any cause and a 34% higher risk of cardiovascular death over 12.85 years. The authors estimated 15 to 30 extra minutes of daily physical activity could offset that added risk. (jamanetwork.com) The new timing study adds a narrower claim to that broader evidence base. Moving still matters, and for some people, matching workouts to when their body is naturally ready may improve how much they get back. (openheart.bmj.com) (jamanetwork.com)
