The Timing of Exercise

Is it time to train? - Exploring the Best Time to Work Out 

You’ve probably heard the question: “Is it better to exercise in the morning or evening?” As with most health debates, the answer is nuanced. And so, as is commonly the case for such questions - it depends (and it doesn’t).

Spoiler alert: The most important variable might not be the clock—but the calendar. But keep reading for more details.

Early Research, Ongoing Questions

The role of exercise timing is still being explored. In fact, many early exercise physiology studies didn’t even record what time of day participants trained, much less control for it. More recent research has started to examine circadian rhythms, hormonal fluctuations, and performance metrics throughout the day—but the question is far from settled. Physiologically, it makes sense that there would be differences. Our body temperature and heart rate start off lower earlier in the day, with fluctuations in our cortisol and hormones in response to our circadian rhythm, our body’s ability to exercise and response to it is likely to fluctuate with them. However, while some patterns are emerging, differences tend to be modest, and individual variability plays a large role.

Okay – what if my main goals are performance? 

If your goal is to prepare yourself for the next race or event, or you are focused on improving endurance, VO2 max, or strength, here’s what we know.

Strength

Looking at systematic reviews of studies show that expression of strength may be slightly superior in afternoon exercises. In effect, this means that afternoon exercisers were able to lift slightly more than their early morning counterparts. And while that may be enough evidence to hit the snooze button a few more times and head to the gym later, you should know that despite this trend, there were no significant differences in overall strength improvements and muscle growth (1). Essentially, if your focus is muscle growth and strength building, do what works best with your schedule.

Endurance

Let’s take a look at the endurance data for marathon runners or cyclists. Current research suggests that performance is again slightly improved in the afternoon, with VO2 max and time-to-exhaustion being higher for the afternoon workouts (2). However, this doesn’t necessarily tell us it’s better to work out in the evening but does suggest that you might not be able to compare your afternoon max-effort performance with an early morning one.

To answer if more improvements are seen with afternoon exercise, researchers performed a (small) study comparing athletes assigned to morning, afternoon, or evening. The afternoon group was able to show the most improvement in VO2 max (3). However, the morning group showed improvements in heart rate response, while the evening showed improvements in lactate response, suggesting improvement for all groups.

To make things even more complicated (or simpler depending on your perspective), it may be more beneficial for you to exercise at the same time as your planned event or race. Training in the afternoon will have the extra benefit of further increasing your ability to perform in the afternoon, while training in the morning will add to your ability in the morning (4).

As a majority of these training differences are small, training specificity (i.e., training at the time of day your event occurs) may matter more than universal rules.

Alright, but I just want to be healthy, does timing matter for me?

If you're prioritizing health, there are several studies that have looked further into factors such as blood pressure, glucose control, and even mood in relation to time of day.

Psychology and exercise

While research is mixed, many participants feel that the perceived exertion or effort needed to exercise later in the day is reduced. However, the overall impact in mood regulation, such as anxiety, has not shown a significant difference based on time of day (5).

Cardiovascular Health and Metabolism

This area of research probably has the most popularity, as well as the most mixed results!

One study compared women exercising at various times of day and various points in their menstrual cycle. The results showed only subtle differences, without clear advantages from a long-term health perspective based on exercise timing (6). Other studies show a lack of significant difference in weight (7), sugar control (8), or overall health (9).

Nevertheless, there is plenty of research to suggest that morning workouts may have a slight advantage over afternoon exercise in reducing risk of heart disease and improvement metabolic health (such as weight and blood sugar control) (10). This was a rather larger and well-done review. Encouragingly, both exercise groups showed improvements in fat loss, decreased waist circumference, and improvements in diastolic blood pressure (the bottom number). The early morning group, however showed a bit further blood pressure reduction (in the systolic or top number), as well as in blood sugar regulation (insulin resistance).

Not to fret, afternoon/evening exercisers – there are still several studies showing benefits here, as well. A study looking at insulin resistance and liver fat content showed that those who were most active in the afternoon and evenings had improved insulin numbers (ie. Blood sugar control) and lower liver fat (another sign of improved metabolic health). Further studies support this, showing reduction in fat mass, sugar control, and other metabolic health parameters in a retrospective review comparing afternoon exercise to morning (11).

“Why did you just go into detail in several studies that seem to conflict or differ?” you might ask. My point here is not to highlight the conflict in these results, but simply to show that the benefits of exercise can be seen and demonstrated at all throughout the day!

Well, let me add one caveat. You may not want to push it too late.

A common concern is whether evening exercise might interfere with sleep. As always, individual response matters. Some people may find a late workout energizing and others find it relaxing. A light jog, walk, or even yoga can be a great way to unwind and end your day. However, it may not be wise to start a vigorous workout just before bed, as research has suggested worsened sleep metrics, including taking longer to fall asleep, reduced sleep quality, and higher sleeping heart rate (12). For such vigorous exercise, it is likely best to conclude these ~4 hours prior to going to bed.

So... When Should You Work Out?

If I’ve taught you anything from this blog post, it’s that I’ve taught you nothing from this blog post. While there are subtle physiological and psychological differences in how our bodies respond to exercise at different times of day, the most important takeaway is this: consistency beats perfect timing. (As many investors might tell you “Time in the Market beats timing the market.”) 

If your goal is to race at 7 a.m., training early can help. If your schedule allows only for lunchtime movement, go for it. If strength is your jam and you feel strongest in the evening, lift then. Our bodies care more that you showed up rather than what time it is.

You don’t need to wait to find the perfect or optimal time for exercise. Simply finding the time that works your schedule is the best outcome. We all have busy lives: work, travel, families, friends, studies, and sleep. Anything you can do to keep your routine consistent will reap the most rewards.

In short: the best time to exercise is the time you can stick with, and that’s a timeless truth.

Sources and Further Readings:

1. Grgic J, Lazinica B, Garofolini A, Schoenfeld BJ, Saner NJ, Mikulic P. The effects of time of day-specific resistance training on adaptations in skeletal muscle hypertrophy and muscle strength: A systematic review and meta-analysis. Chronobiol Int. 2019 Apr;36(4):449–60. 

2. Kang J, Ratamess NA, Faigenbaum AD, Bush JA, Finnerty C, DiFiore M, et al. Time-of-Day Effects of Exercise on Cardiorespiratory Responses and Endurance Performance—A Systematic Review and Meta-Analysis. J Strength Cond Res. 2023 Oct;37(10):2080. 

3. Torii J, Shinkai S, Hino S, Kurokawa Y, Tomita N, Hirose M, et al. Effect of time of day on adaptive response to a 4-week aerobic exercise program. J Sports Med Phys Fitness. 1992 Dec;32(4):348–52. 

4. Chtourou H, Souissi N. The Effect of Training at a Specific Time of Day: A Review. J Strength Cond Res. 2012 Jul;26(7):1984. 

5. Trine MR, Morgan WP. Influence of Time of Day on Psychological Responses to Exercise. Sports Med. 1995 Nov 1;20(5):328–37.