It’s a very common question, and is often accompanied by follow-up questions such as ‘will I burn more fat if I exercise before breakfast?’ and ‘is it bad if I exercise late at night?’. It’s difficult to provide an overall answer to this question because each of us will respond slightly differently. However, we will cover some of the basics in this article and then let you determine what would suit you best!

There are two elements to this question that we would like to answer, one is based around your circadian rhythm, that is your synchronisation between the earth’s 24-hour rotation and your biological function. The second is, of course, the impact of weight and other physiological markers such as cardiorespiratory fitness.

Exercise and your circadian rhythm

A circadian rhythm is a natural, internal process that regulates the sleep-wake cycle. It repeats every 24-hours in line with the earth’s rotation. It helps to regulate the timing of the release of certain hormones, including the sleep hormone melatonin, along with a whole host of other biological functions.

If you’d like to learn more about circadian rhythms, you can read this article by the Sleep Foundation.

So, how does exercise impact this? Your circadian rhythm is affected by daily time cues known as ‘zeitgebers’. Bright light is considered the most important zeitgeber, however, recent research has shown that exercise has a very similar impact in terms of its ability to shift our circadian rhythm.

A study compared the impact of exposing participants to extremely bright light between the hours of 10:10pm and 11:40pm, and undertaking moderate intensity exercise of the same duration between these times. What they found was that exercise had a very similar impact on the participant's circadian rhythm. Effectively, their bedtime was pushed back, and they didn’t want to sleep until later in the evening.

Why is this important? Let’s take a look at an example. If you currently have a regular sleep routine where you go to sleep at 10pm and wake up at 7am, you wouldn’t want any external factors disrupting this cycle, which could have a negative impact on your health.

Timing your exercise within this cycle would make sense, whether that be before work, in your lunch break or straight after work. But if you start exercising earlier in the morning, or later at night, this could disrupt your current rhythm.

Exercise timing, weight loss and physiological markers

Surprisingly, the timing of exercise and its impact on your weight and fitness is not a subject that has been extensively researched. However, a group of researchers from Australia conducted a trial to try and uncover some answers. A group of overweight and obese adults with low levels of activity were put into one of three groups, the early morning exercise group, the evening exercise group and the control group (no intervention). Both groups performed exactly the same exercise in the same environment.

What the researchers found was that both times of exercise had a similar positive impact on weight, waist circumference and other metabolic markers such as blood glucose, cholesterol and blood pressure. This trial only had a small sample size of 19; however, it’s the first of its kind and does suggest that it might not matter what time of day you exercise, you will gain similar benefits across the day.

The researchers did note that adherence to exercise was the most important factor. So whatever time of day you find you’re comfortable exercising, and the time of day that you will continue to exercise, is probably the best! If you’re not sure what time that is, experiment!

Why not try exercising at different times over the next couple of weeks and see which time suits you best?

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