Is exercising in the morning or in the evening better?

Whether morning or evening exercise is better depends on what you are specifically trying to achieve. Science shows that both times of day have advantages, but for different goals. There is no universal winner.

For body fat reduction and a healthier blood lipid profile (cholesterol and triglycerides), morning exercise performed better in a 12-week RCT with 58 sedentary men. The morning group (exercising between 6 and 8 a.m.) already showed greater fat reduction after 4 weeks than the evening group. In addition, total cholesterol and triglycerides only decreased in the morning group. An additional explanation: participants who exercised in the evening ate an average of 152 kilocalories more afterwards than morning exercisers, without feeling any hungrier. That unconscious extra eating can work against fat-loss goals.

For cardiovascular health, evening exercise had an advantage in that same RCT: better blood flow velocity, greater dilation of the carotid artery, and a stronger reduction in systolic blood pressure. In a large observational study (92,139 participants from the UK Biobank, followed for more than 7 years), exercising at any time of day was associated with lower mortality risk. Midday and afternoon exercise (11 a.m. to 5 p.m.) was associated with slightly lower all-cause and cardiovascular mortality than morning exercise, but evening exercise (5 p.m. to midnight) did not show that difference. Importantly, this is an observational association, not evidence that the time of day is the cause.

For sleep and the biological clock, morning exercise is beneficial: it advances the onset of melatonin and the sleep timing, pointing to a positive shift in the day-night rhythm. Both exercise groups fell asleep faster than the control group that did not exercise. Evening exercisers who use caffeine as a pre-workout do face a risk: a high dose (400 mg, equivalent to four cups of coffee) within 12 hours of bedtime seriously disrupts sleep. A normal dose of 100 mg had no effect.

Your own biorhythm (chronotype) also plays a role. People with an evening chronotype (naturally active late in the day) more often have excess weight and worse metabolic values than morning types, partly due to late eating and less healthy eating behaviour. Results for mood and athletic performance in evening types are inconsistent: night owls appear to be more sensitive to the timing of exercise than early birds, but the studies are too small and too variable to draw firm conclusions. Finally, in elite boxers, markers of muscle damage, oxidative stress and inflammation were lower after morning sessions than after evening sessions, but this applied to trained athletes, not to the average recreational exerciser.