Why a morning run is best for your heart, but evening squats help you sleep: Read our guide on WHEN to exercise for the biggest benefits
Exercising in the morning rather than later in the day could cut the risk of developing atrial fibrillation (AF) – a heart rhythm disorder that affects more than a million people in the UK and is a leading cause of stroke.
New research shows working out between 6am and noon cuts the chances of developing the condition by 21 per cent, whereas exercising in the afternoon or evening reduced the risk by about 14 per cent, reported the European Journal of Preventive Cardiology.
Exercise, in general, is beneficial to the heart as it lowers blood pressure and makes the heart pump more efficiently. It’s not clear exactly why morning exercise is better, but the researchers said it’s possible that it coincides with a natural dip in blood pressure.
In healthy people, blood pressure drops 10-20 per cent at night as nerves that respond to stress during the day (driving up blood pressure and heart rate) are naturally less active.
Research shows working out between 6am and noon cuts the chances of developing atrial fibrillation by 21 per cent
The theory is that early-morning exercise extends the duration of this natural event. This protects against high blood pressure – a risk factor for AF – for longer.
Around 1.4 million Britons have AF, where the nerves that regulate the heartbeat go haywire, causing an irregular pulse. In most cases, the heart beats fast (150 beats per minute or more; normal resting pulse is between 60 and 100), resulting in breathlessness and fatigue.
The condition causes blood to accumulate in the left ventricle, the main pumping chamber, which can lead to clots that then travel into the blood vessels that feed the brain, blocking them and causing a stroke.
Treatments include blood-thinning drugs and cardioversion, where the heart is shocked back into normal rhythm using electrodes. Cardiologists also use ablation – burning off the cells where the abnormal signals are coming from.
Exercise has long been known to protect against AF, as it combats high blood pressure.
By exercising in the morning, the body is not subject to a night-time surge in adrenaline which can raise blood pressure
In the latest research, scientists studied more than 88,000 UK adults in their 60s for a seven-year period.
The results showed a distinction between the benefits of morning (6am to noon), afternoon (noon to 6pm) or evening (6pm to midnight) workouts that were seen only in those averaging at least 20 minutes a day of moderate (brisk walking) to vigorous (e.g. running) activity.
Those with high blood pressure benefited most. ‘Some studies suggest morning exercise is more beneficial,’ says Professor Michael Papadakis, an honorary consultant cardiologist at St George’s University Hospitals NHS Foundation Trust.
‘One theory is that this is because it accentuates the dip in blood pressure that occurs at night.’
Another, he says, is that by exercising in the morning, the body is not subjected to a night-time surge in adrenaline which can disrupt sleep and raise blood pressure – heightening the risk of AF.
‘But any exercise, at any time of day, is still a good thing in terms of reducing your risk of atrial fibrillation,’ adds Professor Papadakis.
‘The last thing we want is for people who can only exercise in the evening to reduce the amount they do.’
Measures such as standing up and walking about a bit if you’re at a computer, or just going up and down the stairs a few times, can really make a difference
Yet other studies do point to specific advantages to being active earlier in the day.
Research in BMC Sports Science, Medicine and Rehabilitation in April, found that when obese students were asked to run in the morning or evening five times a week for three months, those who ran between 7am and 10am lost more weight than those between 6pm and 9pm.
Researchers said one reason may be that overnight fasting means the body is more likely to burn stored fat during an early-morning run – as long as no food is consumed prior.
But working out in the evening can have specific benefits, too.
A 2024 study in BMJ Open Sport & Exercise Medicine found that doing just three minutes of exercises (including chair squats, sitting then standing from a chair without using your arms) every half an hour or so in the evening starting from 5pm could improve how much uninterrupted sleep people get by almost half an hour – possibly by increasing levels of the sleep-related hormone, melatonin.
And a 2019 study in Diabetologia revealed afternoon high-intensity interval training – short bursts of very intense exercise – was more effective at lowering blood sugar levels than morning workouts in men with type 2 diabetes.
It’s thought this may be because exercise makes the body’s cells more sensitive to insulin, the hormone that helps muscles convert blood sugar into energy.
As insulin is more effective in the afternoon (because of the body’s energy requirements in the day), post-lunchtime workouts are thought to heighten this effect.
But it need not be a hardcore gym session to get the benefits, says Professor Papadakis.
‘Simple measures such as standing up and walking about a bit if you’re at a computer all day, or just going up and down the stairs a few times, can really make a difference,’ he says.
