When is the best time of day to exercise?

A new study suggests that early morning exercise is best for weight loss. (Getty Images)
A new study suggests that early morning exercise is best for weight loss. (Getty Images)

What's happening

The best time of day for exercise has long been a topic of debate, a fact indicated by the reams of research — some of which has made the case for morning activity and some of which has made the case for evening. The latest conclusion, from the Obesity Research Journal, says that early morning is favored for its promising association with weight loss. However, that's not the only goal with physical activity.

Other studies have evaluated different benefits for specific-time-of-day workouts by studying the impact on a person's body and physiological processes. While that of course includes weight loss, it also includes implications for muscle mass, energy and sleep patterns. To say that exercising at one specific time of day is the only way to achieve positive change in all of those areas, however, might not be possible.

Here's what you need to know about the research on the best time of day to exercise.

Why there's debate

The new review of data on 5,285 participants, published Sept. 4, provides fresh perspective when it comes to the impact morning workouts may have on weight loss, as it surveyed the association between moderate to vigorous physical activity (MVPA) and obesity. Participants were split into three clusters — morning, midday and evening — to determine if they showed significant differences in body mass index (BMI) and waist circumference, two measures of obesity.

The morning cluster, which engaged in 150 minutes of activity per week between 7 and 9 a.m., had the best results, seeing a continuous decrease in BMI and waist circumference. Those who worked out for the same amount of time either midday (11 a.m. to 2 p.m.) or evening (5 to 8 p.m.) didn't see the same results.

"Our findings substantiated the role of morning MVPA in weight management," the study reads. A clinical trial is still necessary.

"My cautious suggestion from this study is that if we choose to exercise in the early morning, before we eat, we can potentially lose more weight compared to exercise at other times of the day," lead researcher Tongyu Ma, a research assistant professor at the Hong Kong Polytechnic University, told NBC News.

However, Ma noted that the results from this analysis might be impacted by factors outside the time of activity, such as age or different responses to exercise.

The best time for exercise is not a simple conclusion to make, as evidenced by the countless other studies and trials that have been conducted on the topic — particularly since physical activity has a positive impact on many different health metrics, such as stress levels, energy levels and sleep, some of which have not been taken into account in past clinical trials.


Evening exercise is optimal for strength training

A 2012 study indicated the body is primed for exercises requiring short and intense bursts of activity in the evening. The same activities may be more difficult to perform in the morning. "Research suggests you might have longer and stronger workouts later in the day than in the morning," fitness expert Jillian Michaels said in Shape.

Despite that study's observation of greater strength in the evening, a 2019 study suggests that increases in strength and muscle size from a strength-based workout are the same day and night.

Aerobic exercise can be done at any time

Aerobic activity, the type of workout primarily responsible for weight-loss management, isn't as impacted by time of day as strength-based exercises are, a 2017 study found — meaning aerobic exercise is just as effective no matter the time of day. However, fasted exercise — working out after a 10-12 hour span of not eating — can increase fat loss for up to two hours after physical activity. "This makes morning sessions the most practical," sports dietitian Lori Russell said in Byrdie.

Sleep is likely to be disturbed by late-night workouts

But it depends on the type of activity. According to strength and conditioning coach Eric Curry in Science for Sports, "Exercising later in the night may hinder sleep quality because it is harder to sleep with an increased heart rate and core body temperature. If late night is the only time you can fit in a workout, selecting less vigorous exercise such as yoga and avoiding high-intensity exercise is suggested."

Morning exercise may be more consistent

Keeping the timing of physical activity consistent helps turn exercise into a habit — and staying consistent is easier to do when working out in the a.m. "Mornings are better for most people because they have more control over their time before the commitments of the day kick in," noted exercise physiologist Ciarán Friel in the New York Times. "You’re usually not being asked to work or do errands at 7 a.m. Friends rarely invite you to happy hour at 6 o’clock in the morning."

Early workouts can turn you into a morning person

Sleep patterns, body temperature, hunger and hormones are all part of natural daily rhythms that are impacted by existing biological and physiological functions. However, experts and studies have shown that such factors are malleable, so making an effort to wake up earlier for a morning exercise routine will eventually feel more natural. "What we’re trying to do is not just shift your bedtime, but actually shift your entire circadian clock to be earlier," cognitive neuroscientist Kimberly Fenn told the New York Times.

Bottom line: The best time for exercise is whenever you want to do it

Personal preference can't be dismissed when it comes to evaluating the effectiveness of a workout, a 2021 study confirmed. As Marisa Mickey, assistant professor of exercise science at Endicott College in Beverly, Mass., told Real Simple, "The best time to exercise is when you can take time for yourself and put your full effort into completing your workout."