The best time to work out: there’s a science to it

Categories: Training

The optimal time of day to train is not usually something that people think about, yet there is a science to optimizing your training times. By carefully planning your training schedule in accordance with your circadian rhythm, you will be stronger, faster and more powerful. After the training, you will gain more muscle. You will also increase your flexibility, reduce your chance of injuries and possibly sleep better.


Sounds too good to be true? Several studies have looked at long term muscle size and strength gains in groups training at different times of day. Even when people are consistent with their training times, strength increases are generally slightly higher and muscle gains up to 84% higher have been found when training in the evening instead of the morning.


The science

Küüsmaa et al. (2016) studied the effectiveness a training program performed in the morning between 06:30 – 10:00 h or in the evening between 16:30 – 20:00 h for a 24 week period. While strength and endurance performance improved similarly across the groups, the men training in the evening gained notably more muscle mass: see the graph below.


best time to work out Kuusmaa 2016 CSA


In line with the increased muscle growth, muscle anabolic signalling after a workout is higher in the afternoon than in the morning  [2].


Laczo et al. also presented the following data at the 7th International Conference on Strength Training in 2010: more leg muscle growth after an afternoon training program than a morning one.


Best time to work out AM vs PM

Malhotra et al. (2014) studied how training in the morning vs. the evening affected strength development. Strength gains were significantly greater in the evening for eccentric exercise: 29% vs. 23%. For concentric training, the trend was the same but less pronounced in favor of evening training with 23% vs. 21%.


Tim Scheett performed a study in bodybuilders on the best time to work out. Half of the participants trained before 10 AM in the morning, the other half after 6 PM in the evening. While the results never got published outside of the 2005 NSCA conference and didn’t reach statistical significance because of having only 16 participants in the study, look at the data below: the evening training group had much more favorable body composition changes.


AM vs PM Scheett study results


Sedliak et al. (2009) studied trained men working out around either 8 AM in the morning or 6 PM in the evening. While again there were no statistically significant changes in strength development or muscle growth, look at the data of muscle growth. It’s likely the difference in muscle growth did not reach statistical significance because of insufficient statistical power, considering there were only 7 and 9 men in the training groups and the study only lasted 10 weeks.


Best time to work out Sedliak 2009


Not all research shows benefits to training later. Sedliak et al. (2017) found similar anabolic signalling, hormonal effects, muscle growth and strength development in untrained men over the course of a training program performed either in the morning or the afternoon. However, with only 7 and 11 subjects in the 2 groups, this study was statistically underpowered to detect even a medium effect size. They couldn’t even find significant correlations between the different measures of muscle growth, so if there were benefits of training in the afternoon, as the other research suggests, they may well have been masked by the large variation in the data and this study simply wasn’t powered enough to detect it. Plus, the former study by these researchers only detected the effect after week 11, but this study was only 11 weeks in duration.


What kind of magic is going on here? Why would the time of day affect how much muscle you gain after a workout? It’s because of your circadian rhythm.


Circadian rhythm 101

Your circadian (sir-kay-dee-an) rhythm is a daily cycle of biological activity. The biological activity with the most obvious circadian rhythm is your sleep-wake cycle. Think of your body as having an internal clock that regulates when to activate every system. Actually, the part of your brain called the suprachiasmatic nucleus (SCN) has built-in molecular oscillators that function very much like a pacemaker. That’s why the SCN is often called your internal or biological clock. The SCN interacts with virtually every major system in your body, including hormone production and central nervous system activity. Look at the image below for examples of biochemical and physiological events with a 24 hour biorhythm. [1]


24 Hour Human Circadian Rhythm


Note that the clock times are relative to your lifestyle and environment, most importantly when you sleep, work and see daylight. Think of the clock times as averages for a regular Joe in the US that works 9 to 5 and sleeps 12 to 8.


For athletes, systematic daily variations in core body temperature, energy metabolism and hormonal milieu are the most important factors influenced by your circadian rhythm. Let’s first look at testerone, the alpha hormone, and cortisol, the stress hormone.


The T/C ratio and maximum anabolism

It’s common knowledge that high testosterone levels are anabolic and thus beneficial for muscle growth and strength development, whereas cortisol has catabolic effects and excess levels can be detrimental. Accordingly, the testosterone to cortisol ratio or the T/C ratio is commonly used as a marker of tissue anabolism and a measure of overtraining [1, 2]. With this in mind, it may be beneficial to train at a time of day when the T/C ratio is highest.


Testosterone production is high at night and low during the day: see the graph below.


 Testosterone circadian rhythm


Cortisol output is low at night, rapidly rises during awakening and then gradually decreases over the course of the day.


Cortisol circadian rhythm


As you can extrapolate from the above graphs, the T/C ratio is highest in the afternoon and evening [1, 2, 3]. During this period, exercise causes the smallest rise in cortisol and the largest increase in testosterone [1, 2]. Other research has found that rugby players gain more strength and mass with a strength training program that elicits high testosterone stimulation compared to one that elicits low testosterone stimulation.

Cortisol elevation also recovers fastest after training later in the day.


It is very plausible that the hormonal milieu in the late afternoon is optimal for maximum muscle anabolism. However, the research is still contentious about how transient fluctuations in hormone concentrations relate to muscle growth [1, 2, 3].


Core body temperature

Much less contentious are the effects of your core body temperature. Core body temperature is the temperature at which your central organs operate. Enzymatic reactions are extremely sensitive to minor variations in your core body temperature. For the biological systems involved in high intensity physical exercise, the optimal temperature is relatively high. High core body temperatures improves nerve conduction velocity, joint mobility, glucose metabolism and muscular blood flow. Most people can achieve higher muscle activation levels in the evening compared to the morning. As a result, core body temperature correlates with exercise performance. People are normally strongest when their core body temperature reaches its daily peak.


Core body temperature is low at night, rises quickly upon awakening and reaches a maximum in the evening: see the graph below.


Core body temperature circadian rhythm


For the older readers, peak performance for strength training in middle aged adults occurs earlier than in adolescents. In the temperature graph above, the black dots represent older subjects.


The optimal body temperature for strength training normally occurs in the late afternoon to early evening [1, 2, 3]. That’s when flexibility, power and muscular strength reach their daily peak.


Accordingly, most sports records are broken in the early evening.


The peak performance time (acrophase) differs per activity. For example, swimming performance peaks a few hours later in the evening than most ground based activities. In general, endurance capacity seems to have a less pronounced circadian rhythm [1, 2]. See the table below for an overview of the peak performance time for various studied performance measures [1].


Best time to work out performance acrophase review


Greater performance can obviously lead to greater muscular adaptations. Together, the anabolic hormonal milieu and the greater performance resulting from a higher core body temperature can explain why research finds greater muscle growth rates and strength development when training later compared to earlier in the day. This begs the question: what’s the optimal time of day to train?


The best time to work out

Based on the circadian rhythm of your hormones, gene expression and your core body temperature, the best time to schedule your training sessions is between 14:30 and 20:30 h if you have a normal biorhythm and sleep during the night from roughly 12:00 – 08:00 h.


For those with an irregular sleep-wake cycle (read: students), it’s preferable to wait at least 6 hours after awakening before training. The optimal training time will then be closer to 20:30 h than 14:30 h.


However, different people can have a significantly different biorhythm. Peak performance and exercise adaptations correlate strongly, so a good rule is to train when you personally perform best [1, 2]. The individual variability probably also explains why the research isn’t all consistent. Some people are true ‘early birds’ and they show far less loss of performance in the morning than typical ‘night owls’. People also vary in the extent to which they can adapt to morning training. So some people can do just fine training in the early morning.


When experimenting with at what time your performance is optimal, you can use your heart rate as a guideline. Resting heart rate and core body temperature are strongly correlated. Therefore, the time of day when your resting heart rate peaks is often the best time to train. Unfortunately, simple oral or insulated axilla (under the armpit) temperature readings are too noisy to measure your circadian rhythm [2]. The scientific gold standard is sticking a thermometer up your ass, but that’s probably reserved for the real die-hards. As some researchers put it, “Core temperature is often measured using a rectal probe, a thermistor inserted 10 to 12 cm [4 to 5 inches] past the anal sphincter. Participants are not always comfortable with this site […]”.


What if you can’t train at the optimal time?

Not everyone has time to train at the physiologically optimal time. However, for most people this is just an excuse. “Not having time” to train actually means “I value training less than the thing I’ll do instead”. The things you make time for are the things you prioritize. In Dutch, the word for priority is pronounced as the Dutch equivalent of ‘prioritime’. Time equals priority.


That said, it’s a reality that not everyone has the luxury of planning their training sessions during the physiologically optimal times. Plus, life doesn’t always go as planned. Our schedules have to consider our work, study, family and other day to day activities. So what’s a Bayesian with a genuine scheduling problem to do? You have two options to train in the morning or at night without having your training sessions suffer much as a result.


Strategy 1: Caffeine

Caffeine effectively forces your body into daytime mode. That’s why it helps counteract sleep deprivation so effectively. A dose of ~250 mg (3 mg/kg) caffeine in the morning raises neuromuscular readiness to perform close to afternoon levels.

As you can see in the graph below, there was still a trend for lower performance in The AM + caffeine group compared to the PM group, even though the PM group didn’t consume caffeine, but this difference was not statistically significant. This may well have been due to the small sample (N = 12) and resulting insufficient statistical power to detect the performance decrement.


Best time to work out caffeine effect


There are several reasons why taking caffeine in the morning as a pre-workout may not be 100% optimal.

  • Caffeine decreases the T/C ratio.
  • Caffeine doesn’t elevate morning growth hormone levels to afternoon levels.
  • If you consume more than 50-100 mg of caffeine daily, you’ll develop a tolerance to caffeine’s ergogenic effects.
  • Consuming caffeine at night can interfere with your sleep.


Strategy 2: Consistency

The second strategy to increase your performance when training at a suboptimal training time is to make sure you always train at that time. Your body will adapt its circadian rhythm to the morning training stress and reduce the performance decrements at that time [1, 2].


However, it seems your biorhythm cannot perfectly adapt to training in the early morning to the extent that performance is 100% unaffected compared to training later in the day. The nervous system adapts reasonably well, but physiological systems such as hormone production adapt less well. This corresponds with the trend in research that muscle growth is more strongly affected by training in the morning than strength development is.


Your body also acclimates to training in the early evening by increasing the circadian variation in performance throughout the day. As such, it is still best to train when your body is biologically primed to do so, because you’ll prime it even further to train at this time.


However, with meticulous circadian rhythm control using supplementation, light therapy and consistent nutrition and training, you can shift your optimal training time greatly and you can achieve comparable results when training in the morning compared to training later in the day.


The exception to the rule

If you have a job that is particularly stressful, it may be better to train during lunch than after work. Mental stress, such as very high responsibility or long commuting and physical stress, such as manual labor, can take its toll on the body. The fatigue from work may then offset the benefits of the optimal physical state later in the day. At least one study shows that in shift workers peak performance occurs before work, followed by lunch, followed by after work. So if your work is particularly fatiguing, it may be best to schedule all your training sessions before work or during lunch. Note that this particularly holds for physical fatigue, not necessarily mental fatigue.



Not many people think about when the best time to train is. Even fewer have the discipline to schedule their training sessions when they are biologically primed for maximum performance. It’s a shame to put in countless hours in the gym at a time when your body is not in top gear and can’t recover optimally from the training. By following this guide you can optimize your training schedule and fast-track your gains. All without training more or changing your diet.


Of course training in the first place is more important than when you train, so if your schedule prevents you from training in the afternoon, getting in your workouts whenever you can is priority number one. If you’re a natural morning person, this may work perfectly well for you.


Take home messages

• Your circadian rhythm is a 24 hour cycle of biological activity set by your internal clock. Your sleep-wake cycle is one of many systems influenced by your circadian rhythm.
• Your hormonal milieu, gene expression and core body temperature have a circadian rhythm. Together, they result in peak physical condition to train and recover in the late afternoon to early evening for most individuals.
• The best time to work out is generally between 14:30 and 20:30 h if you have a regular sleep-wake cycle.
• You can determine the optimal time to train by monitoring your maximum resting heart rate and training performance. Some people do just fine training in the morning.
• If you can’t train when your body is primed to do so, supplement with caffeine pre-workout and schedule your workouts when you can always train. Getting in your workouts in the first place is of course always more important than when you do them.


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About the author

Menno Henselmans

Formerly a business consultant, I've traded my company car to follow my passion in strength training. I'm now an online physique coach, scientist and international public speaker with the mission to help serious trainees master their physique.

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