A Few Caveats

As with any kind of “what works better” discussion, the answer has to come with the qualifier “all other things being equal.” And of course, all other things are not always equal.

This is relative to when you wake up, not the clock

The studies and methods quoted above have all found an optimal training time somewhere between 3 p.m. and 9 p.m. That is not, however, an absolute.

In this case, timing matters relative to your biological clock; the exact time of day isn’t really the issue here.

The subjects in these studies were all sleeping on a fairly normal schedule, waking up around 6–9 a.m. and going to sleep around 10 a.m. –12 p.m. That corresponds to a training window between six and fourteen hours after waking up. In practice, however, the truly optimal training window — for most people, anyway — corresponded to a time period more like eight to twelve hours after waking up.

You have to do what fits your schedule

A good strength training workout takes time, and usually requires a gym — at least if you plan to lift heavy weights and perform a variety of exercises. That means you need at least an hour to spare, and often more.

Making the time to work out is at least as important as working out at the (physiologically) optimal time of day. It’s better to do a complete, hour-long workout in the morning with proper rest periods than a rushed, incomplete workout at 5 p.m.

That said, most people can make time somewhere in that optimal window, which again is pretty broad. When people “don’t have time” to work out, that almost always means they actually have the time and spend it on something else they value more. In other words, you “don’t have time” for something in addition to all the stuff you’re already doing.

Stress matters

Your stress levels have a huge influence on your ability to recover from exercise — the difference between high and low stress levels can easily equate to a twofold difference in recovery capacity and muscle-building potential.

Cortisol, the body’s main stress hormone, also causes the human body to store more belly fat. Thus, people who are training to lose fat are likely to be disappointed by the impact on their waistline if they train when they’re stressed out.

Some people have very stressful lives, and in particular, very stressful jobs. For people working a typical 9–5 schedule, training at the optimal time usually means, in practice, training right after work.

If you’re commonly stressed out at the end of the workday, this probably won’t be ideal. It’s better to exercise when your stress levels are lower, even if it’s a little outside the optimal training window.

Training later in the evening usually isn’t an option either — people with very stressful jobs usually don’t have the energy for it later in the evening and prefer to spend the whole evening relaxing. The big exception here would be if you do find exercise relaxing, particularly if your gym is also near your home, allowing you to unwind a bit after work before walking over to the neighborhood gym.

But for most people, this situation — being stressed out at the end of the workday — will necessitate training earlier in the day. Lunchtime would be preferable to early in the morning if you’re able to take a long enough lunch break and have a gym close to work.

At least one study shows that in shift workers, peak performance occurs earlier in the day. So it is certainly possible for your work schedule to shift your peak performance time. However, this only goes so far, as you’ll see in the next section.

While this is earlier than the optimal training window, there are a few ways to make earlier workouts more effective.

You can become entrained to your workout time

Over time, things you do at the same time every day become entrained into your circadian rhythm. You get tired before your typical bedtime. You get hungry before your usual meal times. And, fortunately, your energy level will start to rise in anticipation of your daily workout.

If you train in the morning, consistently, you will start to have more energy in the mornings and your morning workouts will become more productive. Almost anyone who trains in the mornings can attest to this — it’s hard at first, and gets easier over the first few weeks.

Of course, most people don’t train every day. In order to benefit from this entrainment effect, you’ll need to train fairly often — probably at least four days a week at the same time, i.e. training more days than not.

However, studies suggest that this adaptation is only partial. While training in the mornings may give you more energy in the morning, it might not shift your peak core body temperature to earlier in the day.

Fortunately, there is one other tool you can use to shift your biological clock.

Caffeine can make a difference

Caffeine, of course, raises your subjective energy level. And as I discussed in my article on gym motivation, caffeine also motivates you to work out more.

While caffeine’s effects are mostly psychological, it does also raise your core body temperature and levels of muscle activation during exercise, particularly when consumed during the morning.

In one study, people who trained in the morning after consuming 250 mg of caffeine (around 3 mg/kg) showed almost as much neuromuscular readiness to exercise as people who trained in the afternoon without caffeine. Their exercise performance wasn’t statistically different from the afternoon group; however, it was non-significantly lower across the board.

Unfortunately, the dosage of caffeine used in this study is high enough to be problematic. As I discussed in my article on caffeine addiction, taking more than 100 mg per day will lead to a gradual tolerance buildup and accompanying withdrawal symptoms.

Moreover, taking that much caffeine (even first thing in the morning) will impair your sleep later that night, up to 15 hours later.

It’s better, in the long run, to have around 100 mg of caffeine before morning workouts. Acutely, this won’t be as good as a higher dosage, but you’ll see better long-term results when you sleep well and don’t become addicted to caffeine.