Introduction

Everyone knows that exercise is a key component of a healthy lifestyle. It can help us manage our weight, gain strength and stamina, improve our mental health, and reduce the risk of diseases like type 2 diabetes and even cancer.¹

Therefore, it is highly recommended that adults do at least 150 minutes of moderate-intensity activity a week. This could look something like a brisk 20-minute walk every day. Strength training at least 2 days a week is also encouraged to promote muscle growth.²

The proportion of the general population who are overweight or obese is staggeringly high. As of 2023, roughly 64% of adults are estimated to come under this classification.³ It is important to note that, in most cases, diet is the most significant factor contributing to the maintenance of a healthy weight. 

However, with many people having busy work schedules and various life responsibilities, making the best possible dietary decisions is not always easy. On top of this, finding the right time to exercise regularly can feel like an impossible task.

That being said, the benefits we gain from exercise may be influenced by the time of day. Whether you prefer to exercise in the morning or afternoon can impact your sleep, hormones, energy levels, and other aspects of your health. So, when is the best time of day to exercise? This article will take a deep dive into the research on exercise timing and its associated benefits and drawbacks.

The impact of individual preferences and lifestyle

When it comes to planning when to exercise, our personal habits and responsibilities have a major impact on how much free time we have. Morning exercise may be advantageous for some since it allows more time in the afternoon and evening for other things. However, what if you work variable shift patterns or start work early in the morning or late at night? For these individuals, flexibility in terms of exercise timing might be limited.

The timing of our meals might also affect when we feel like exercising. Many prefer to work out on an empty stomach, so it would make sense for these individuals to exercise first thing in the morning before eating. Others might prefer to fuel up before a workout, so in the afternoon after a meal would be an ideal time to fit exercise in.

Our personal fitness goals could also dictate when we should work out. Studies have shown that morning exercise might be better for reducing body weight and blood pressure, and evening exercise might be better for improving muscular performance and decreasing fatigue.^4,5

Other logistical factors (e.g. weather, temperature and access to facilities) must also be considered on a day-to-day basis.

Why is our circadian rhythm important?

The term circadian rhythm refers to the way in which our body chemistry, physiology, and behaviour change over the course of 24 hours; the word circadian is derived from the Latin "circa diem", meaning "one day".

A part of the brain known as the suprachiasmatic nucleus (or SCN) is responsible for setting the pace of our circadian rhythm. After it receives signals, in the form of light for example, it sends out signals to the rest of our brain to trigger hormonal changes. This results in fluctuations in the levels of various hormones in our body, in accordance with changes in light.⁶ For example, at night, the SCN signals to the pineal gland, in turn releasing melatonin (a hormone which induces sleep).⁷ 

Since our circadian rhythm dictates the levels of key hormones influencing our energy and appetite levels, it makes sense to time exercise in accordance with this rhythm.⁸ Interestingly, exercise has been suggested as a “zeitgeber” (a factor that influences the timing of the circadian rhythm), again stressing the importance of exercise timing.^9,10

What are the benefits of morning exercise?

Aside from the practical reasons to choose to exercise in the morning hours, many studies have demonstrated the psychological and physical benefits of morning exercise. For example, one study showed that, after morning exercise, individuals were less likely to have a neurological response to images of food than those who did not exercise. 

This means that morning workouts might make us less distracted by food afterwards. Furthermore, those who exercised in the morning were more physically active for the remainder of the day.¹¹

In a study of individuals with metabolic syndrome performing high-intensity aerobic exercise, a greater reduction in insulin resistance and blood pressure was found in those who worked out in the morning compared to those who exercised in the afternoon.¹²

Cognitive improvements might also be seen following morning exercise. Specifically, in one study, adolescents performing high-intensity interval training (HIIT) exhibited quicker reaction times in computerised tasks when this exercise was performed in the morning compared to the afternoon.¹³

The mantra “consistency is key” is often stressed when it comes to exercise. The results of one study suggest that morning exercise might make practising consistency easier. Individuals who worked out in the morning were found to more often achieve the recommended 150 minutes of moderate-intensity activity a week. Not only this but they were also found to exercise for longer than those who worked out in the afternoon or evening.¹⁴

What are the benefits of afternoon and evening exercise?

After a long day at work, some may find exercise to be a stress-reducer and a good time to relax and unwind before the rest of the evening.

As well as the mental benefits of afternoon and evening exercise, our metabolism might perform better when we wait until the later hours to work out. For example, one study found a lower oxygen consumption with later exercise compared to morning exercise. This means that the exercise efficiency was greater. Since our body temperature is higher later in the day than it is when we first wake up, this might contribute to improved muscle engagement and function.¹⁵ 

Therefore, afternoon exercise might be appealing for those whose focus is more on improving their fitness and strength, rather than weight loss specifically. That being said, greater fat loss with afternoon exercise compared to that with morning exercise has also been reported.¹⁶ Therefore, there is some evidence to suggest that exercising later in the day might offer all-round benefits.

HIIT, a popular form of exercise, has been found to lead to more benefits when performed in the afternoon compared to in the morning. Improved insulin sensitivity, better fasting glucose levels, and reduced fat mass have all been reported.¹⁶ Similar findings have been described for those with type 2 diabetes in particular.¹⁷

Although there is conflicting evidence, it has been suggested that exercising later on in the day can improve sleep quality.¹⁸ However, it has been found that regular night-time exercise can cause a delay in the onset of melatonin release, which could lead to a delay in falling asleep.¹⁹ Taken together, research suggests that exercising shortly before going to bed (e.g., 1 hour before bedtime) might lead to poorer-quality sleep, so this should be avoided where possible.

Summary

• Much of the existing research promotes morning exercise for its positive effects on our mental function, appetite, and energy levels for the remainder of the day
• Exercising in the morning might also be the most practical option for those who wish to complete their workout early on, allowing more flexibility for other activities later
• Afternoon and evening exercise could be the better option for those wanting to optimise performance in their workouts and see results in terms of muscle growth
• Exercising immediately before bed can potentially have negative impacts on our sleep, an important factor contributing to our overall health
• Overall, consistency is key: if we stick to a specific portion of the day in which to exercise, we will be more likely to exercise out of habit