Exercise is essential for good health. But is there a best time to do it? We dive into the science to find out whether working out in the morning or evening really makes a difference.
Getting enough regular exercise is important for vitality and well-being, improving almost every aspect of life - from mood and energy to physical strength and disease risk. Given its undeniable necessity for health - after all, the CDC recommends we get at least 150 minutes of moderate intensity activity each week - scientists have been hard at work trying to determine whether the time of day we exercise matters. Can when we exercise enhance - or dull - the benefits we get from exercise? When exactly is the best time to work out?
Researchers have already discovered that the timing of when food is eaten can influence the body’s circadian rhythm and metabolism, but are just recently starting to study the different effects physical exercise has on the body both in the early morning and later in the day.
Exercise timing: why it matters
The body is hardwired to follow a daily circadian rhythm which regulates practically all of the physical, emotional, and behavioral changes that occur in the body and brain over a 24-hour cycle. A prime example of this “master clock” can be seen each evening. When the sun sets and darkness falls, you suddenly yawn and feel sleepy. This is your body’s way of preparing you for a night of sleep ahead. And when sunlight hits your face the next morning, you perk up and feel more energized, ready to take on the day. Likewise, the body-temperature cycle relies on this internal clock, elevating the body’s temperature during the daytime to prime the immune system to fight invaders off before dropping back down at night while at rest.
Both internal and environmental factors impact the body’s circadian rhythm. For example, incoming light sensed by the eye’s optic nerves is a direct input for the circadian rhythm, letting the body know that it is daytime. Exercise also helps synchronize the circadian rhythm, and because of this, researchers have conducted a number of studies to determine whether the timing of exercise plays a role.
Does the time of day affect weight loss?
Like almost every other physiological process in the body, body weight regulation - that is, the balance between energy intake (calories in) and energy expenditure (calories burned) - relies on the timing of the circadian rhythm. Lifestyle behaviors like when meals are eaten and exercise times may serve as cues for how the body should regulate this balance, ultimately affecting its ability to gain or lose weight.
When it comes to losing weight, evening exercise may not be the best choice, according to one 2020 study. Eighty-eight adults with overweight or obesity underwent a 10-month exercise program where they were grouped into either exercising mostly in the morning between 7:00 AM and noon, mostly in the evening between 3:00 PM and 7:00 PM, exercising at different times of day or evening, or did not exercise at all. Their calories consumed and weight were measured at 3.5 months, 7 months, and 10 months, and their calories burned were measured each day. While there was no notable difference between any of the groups when it came to calorie intake and calorie expenditure, the researchers saw a significant weight loss among those who exercised mostly in the morning (7.2 lb loss) and at any time of day (5.5 lb loss) compared to exercising in the evening (2.1 lb loss) or not exercising at all (0.5 lb loss).
How does exercise timing affect insulin sensitivity?
Exercise has long been recognized for its ability to improve insulin sensitivity, an objective that is particularly critical among people with diabetes. But the timing of a workout might yield variable results when it comes to controlling blood sugar. One 2022 study aimed to determine how movement during the day might affect insulin sensitivity by tracking the activity levels of 775 participants who were grouped into either being most active in the morning (6:00AM to 12:00PM), afternoon (12:00PM to 6:00PM), evening (6:00PM to 12:00AM), or evenly maintained moderate-to-vigorous activity throughout the day. Blood samples were taken before and after eating to monitor insulin responses. After the trial, the researchers found that the participants who were most active in the afternoon and evening improved their insulin sensitivity by 18% and 25%, respectively, whereas those who were active in the morning and throughout the day improved their insulin by only 3%. In other words, compared to morning activity or activity spread out throughout the day, afternoon and evening activity appeared to result in the greatest improvement in insulin sensitivity.
How is exercise performance impacted by the time of day?
In one Finnish study, researchers set out to determine whether exercise performance and muscle building are optimized in the morning or evening. They tracked the physical performance and muscle mass outcomes of 42 young adult men assigned to either morning or evening combined strength and endurance regimens over 24 weeks. The two groups were tested for strength performance using a dynamic leg press, and muscle mass and time to exhaustion were measured. Both groups increased in strength performance throughout the trial, but the evening trainers gained more muscle mass than the morning trainers during weeks 13 through 24. Time to exhaustion also similarly improved among both groups throughout the 24 weeks, although the groups that performed endurance training before strength training both morning and evening saw the most improvements.
Does exercise in the morning versus the evening affect the quality of sleep?
Exercising can improve how well you sleep, but can the time of day further help or hurt your chances of waking up refreshed? The evidence is not totally clear.
One study found that exercising too close to bedtime resulted in lesser quality sleep. The sleep quality of 16 adult subjects was assessed after participating in three sessions spanning three weeks. The sessions consisted of either a non-exercise activity, an early evening one-hour outdoor run four hours before bedtime (6:30 PM), or a late evening one-hour outdoor run one hour before bedtime (8:30 PM). The results showed that sleep quality was higher for the group that exercised in the early evening (6:30 PM) compared to those who did not exercise. An improvement in sleep quality was not seen when exercise was performed in the late evening (8:30 PM). In contrast, a recent meta-analysis found that exercising at night may still improve sleep quality compared to not exercising at all. Current science suggests there is no one best time of day to exercise for sleep. Other factors like your natural tendency to stay up late or head to bed on the earlier side can make a difference in your sleep quality, as well as your age and whether you have any underlying health conditions.
Is a morning or evening routine easier to stick to?
Any exercise is helpful for maintaining health, but incorporating physical activity as a regular part of your lifestyle is key to reaping the most benefit. Given the busyness of life, it is easy to understand why many people prefer to exercise first thing in the morning before the day begins. It turns out, there’s good science that backs this healthy habit up.
Evidence shows that consistency in the time of day that exercise is performed, known as temporal consistency, makes it easier to stick to for several reasons. For starters, it makes clearing your schedule for exercise simpler when you know exactly when you’ll be working out at any given time. Secondly, keeping the time of day consistent goes a long way in strengthening habit formation by creating learned associations between exercise and timing cues. For example, if you start a new routine after drinking your morning coffee, finishing your cup will soon become your mind’s cue to get into the exercise zone.
But is the morning really the best time to work out to achieve a consistent exercise habit? One study suggests so, where 709 physically active subjects reported on their amount of activity, the time of day they exercised - early morning, late morning, afternoon, or evening - and how habitual their exercise was over one year. The authors found that temporally consistent exercisers were most likely to maintain their routines over time, especially if they worked out in the early morning, with 62% of early morning exercisers still continuing to work out during the same time after one year. In other words, the subjects who worked out at the same time each day, particularly in the early morning, maintained their exercise routines even after one year.
The bottom line
The benefits associated with exercise are seemingly endless, from maintaining body weight and heart health to boosting sleep quality, mental health, insulin sensitivity, and bone and muscle strength. Is there a best time of day to exercise, according to science? While there is some evidence to suggest that afternoon exercise may be more effective at stabilizing blood glucose and that evening exercise could result in greater calorie expenditure and muscle mass, most experts agree that exercise at any time of day is more beneficial than no exercise at all. Aim to cultivate a consistent exercise habit that you can enjoy and stick with in the long run.
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