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When Should You Work Out?

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 hitting the gym for a cardio session first thing in the morning makes you feel more energized throughout the day.

Then, you’ve got the people on the other side who are convinced that exercise in the evening is better for you. They claim that the quality of their workouts are much better if they schedule it closer to their bedtime. And oh yeah, you can sleep in!

The reality is, people who are morning people have made it a habit to be active to be active the minute they wake up, and people who are night owls prefer to schedule their interval training after leaving the office. 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 routine that works for them.

But setting aside personal preference for the moment by approaching it from a more scientific angle and asking, “OK, when should I schedule my workout so that I can burn fat, gain muscle, and reach my fitness goal: right after I wake up or closer to my bedtime?”

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 hit the gym to reach your fitness goal.

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 both are easily understood and scientific sounding enough. 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 hitting the weights, 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 exercise 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 of 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 the 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.