Weighing the Facts: When Should You Work Out?
PUBLISHED ON MAY 19, 2016 BY RYAN WALTERS
Talk to some people about when the best time to work out is, and they’ll swear that mornings are best. They’ll tell you getting out of bed earlier has all sorts of benefits, like making you more energized in the morning, feeling better throughout the day, and so on.
Then, you’ve got the people on the other side who are convinced that evening workouts are the superior variety of workout. Evening workout proponents will often say that they feel more energized in the evening and are able to have a better quality workout. Also: no waking up early!
The reality is, people who are morning people just like being active in the mornings, and people who are evening people prefer evening activity. It really depends on what you like, so in one way, both the morning camp and the evening camp are equally “right” because they’ve found a time that works for them.
But setting aside personal preference for the moment by approaching it from a more scientific angle and ask, “OK, when is the best time to work out so that I can maximize results?”
Now here’s where things get interesting.
Below, we’re going to lay out the arguments for both the morning and the evening group, discuss their merits, and conclude whether there IS a perfect time to work out after all.
Warning: we really are going to weigh the facts here. If you just want the quick and fast answer, we totally get it. Click here to jump down to the takeaway.
The Case For the Morning Workout
The case for the morning workout rests on primarily two positions, both of them very popular with the fitness community. They are:
- For muscle gain, exercise when your testosterone levels are at their highest
- For fat loss, exercise fasted so your body draws on fat reserves for energy
What makes these positions so believable is because they both are easily understood and sound scientific. However, if you dig into the research, you’ll find that both of these positions aren’t completely off-base, but they do run into a few problems.
It’s true that testosterone levels are at their highest in the morning and then decline slowly throughout the day. Testosterone is an anabolic (muscle-growing) hormone that is secreted during sleep, much like growth hormone is. Sufficient sleep has very significant effects on body composition and is crucial for both successful muscle development and fat loss, not to mention being super important to having enough energy for the morning workouts in the first place!
The problem is, while high morning testosterone levels might seem ideal for a morning squatting sesh, there's another hormone that’s also peaking in the morning: cortisol.
In the most general of terms, you can think of cortisol as the “anti-testosterone.” Whereas testosterone is an anabolic hormone, cortisol is a “catabolic” (muscle-depleting) hormone, something that does not encourage muscle growth. With both testosterone and cortisol elevated in the morning, any supposed boost to lifting in the morning due to testosterone levels will be largely canceled out.
Now, about morning workouts being better for fat loss. This position is usually linked with the idea of fasted exercise yielding higher fat oxidation (aka “fat burning”), since the idea is you work out before having breakfast and you burn more fat because you don’t have much glycogen (“energy”) from food to draw from.
The truth is, research on this topic is somewhat mixed. In this study of trained, Muslim rugby players who were fasting during the Islamic holy month of Ramadan, researchers found that the players were able to utilize their body fat for energy more efficiently during exercise than they were able to previously, when they were able to eat normally throughout the day.
However, another study published in the American Physiological Society makes a case for the counterargument by showing that while participants who fasted before exercise did have some beneficial effects, in terms of fat oxidation, there was no appreciable difference between the group that fasted and the group that didn’t.
This isn’t to say that there isn’t anything for workouts in the morning. Research conducted at Appalachian State University found that morning walks (7am) on a treadmill reduced blood pressure and improved sleep better than walking in the evening (7pm). While this is certainly a positive benefit, if you’ve previously held that morning workouts are automatically better for your workouts because of testosterone levels or wanting to train fasted, you may not actually be getting much benefit, if any.
The Case for the Afternoon/Evening Workout
The position of those who believe in working out in the afternoon rest on a couple points:
- The testosterone to cortisol ratio is the most conducive to muscle growth in the evening
- Peak body temperature occurs in the afternoon, and is linked with increased strength
As mentioned above, testosterone levels are indeed at their highest concentrations in the early morning, but so is cortisol. If exercising in the presence of increased testosterone levels is desirable, research has shown that the optimal time to exercise is in the late afternoon because of the favorable ratio of testosterone to cortisol that happens during that time.
Where does the research fall on the relationship between body temperature and strength? In addition to the study on testosterone cited above – which found that strength coincided with peak body temperature in the afternoon – there is this study which focused exclusively on body temperature in elite rugby players.
A measurement of strength was taken at two times during the day, once in the morning and again in the afternoon, while recording internal body temperature at each testing period. The study found that in all 16 rugby players, strength was significantly correlated with body temperature: both strength and body temperature peaked in the afternoon.
A plethora of studies that have examined strength as it relates to time of day seem to confirm that muscles are indeed capable of producing more strength output in the afternoon including:
- A study of sprinters tested the strength produced in a series of 10 consecutive sprints performed at two times: between 8-10am and 5-7pm. When the sprinters ran in the evening, they consistently performed better on the first three sprints vs. the first three sprints in the morning.
- A study of cyclists performing a 60-second Wingate test (a test designed to measure anaerobic strength) had their strength and power assessed at one of two times: 6am and 6pm. Strength was measured in three ways: the peak strength, average strength over 30 seconds, and average strength over the 60 seconds. All power outputs recorded in the evening were higher than in the morning
A common concern regarding working out late at night is that evening workouts will disturb your sleep, sabotaging the recovery process. While a definitely valid concern, there isn’t much supporting it. When researchers actually put this concern to the test, in at least three studies, they were unable to find a clear link between vigorous late-night exercise and disrupted sleep.
It may be that exercising at night DOES make it harder for you to fall asleep, and if that’s the case, that’s something you should take into account. However, if you were avoiding evening workouts because you were afraid of losing sleep, but hadn’t tried it for yourself, you may want to give it a shot.
So, What’s the Answer?
It would appear that, based upon the research, the best time to work out – objectively – is in the afternoon. Sorry, morning workout fans.
“But wait!” comes the cry from the morning crowd: “I don’t care what your fancy science and research says. I work out way better in the morning, and nothing you tell me can change the way I actually feel in the mornings.”
To which the research would say: “Guess what, you’re right.”
That’s right: even in the face of all this scholarship, if you feel like you perform better in the mornings instead of the afternoon, you’re most likely right and science would back you up on it too. Let’s explore:
One study that sought to solve the issue of the best time of day to work out had a group of participants exercise for 10 weeks between the hours of 5-7pm. Once done, they were randomized into two groups: one that worked out in the morning between 7-9am and one that continued to work out between 5-7pm. Changes in muscle growth were measured for each.
The results? Yes, the afternoon group experienced a larger percentage of muscle growth compared to the morning group (3.5% vs. 2.7%), but crucially, the researchers found this 0.8% difference not to be statistically significant.
That means the changes weren’t different enough to be outside the realm of pure chance. “But still,” you might say, “given all the research in favor of evening workouts, even in that study, evening workouts came out ahead, statistically significant or not.” Yes, that’s right, but there could be a very reasonable explanation for this.
In a review of training at a specific time of day, researchers noticed something interesting. While agreeing that peak performances typically occur in the afternoon, they noticed that this pattern is not absolute. They found that people who consistently work out in the morning are able to overcome any “limitations” morning workouts may have, and actually exceed their own performances in the evening.
Likewise, for people who do work out in the afternoon, the differences between their morning and evening performance is significantly (and unsurprisingly) in favor of the evening, leading the researchers to conclude:
Therefore, adaptations to training are greater at the time of day at which training is regularly performed than at other times. – Chtourou, et al. (2012)
So now, think about the study before – the one with the evening group having a 0.8% increase over the morning group. Remember how the participants spent nearly three months preparing for the study by training in the evening, and then had some switch the morning? What would have happened if they had prepared by training in the morning? Would the study have had the same results? Hard to say.
We’ve gone through a lot to say pretty much this: while it’s probably better to exercise in the evening, what’s far more important is to a) just exercise b) be consistent with the time you exercise.
Although there’s a lot of research backing up the evening workout, due to your individual situation in life, fitting in a morning workout might make more sense for you. If that’s the case, it’s totally fine. You’re not going to put yourself at any significant disadvantage.
Also, know that an extremely significant factor not mentioned here, nutrition, plays a gigantic role in your fitness performance – maybe enough to make this entire discussion moot.
That being said, if you have the opportunity to work out in the evening, it might be worth testing for yourself. You may find that working out in the evening does, in fact, help you lift more, or run farther/for longer.When you’re doing the same thing, day in, day out, a little boost from your body couldn’t hurt, right?