Sleep well! 8 reasons why a good night's sleep is so important for bodybuilders

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As a bodybuilder you strive for a physique that is massive and lean at the same time: much muscle and little fat. A good night’s sleep plays a crucial role in achieving that dual goal. You’ve undoubtedly been told this often enough, but why is it so? Eight reasons in a row.


Your body uses nighttime sleep to repair damage you’ve sustained during the day. A wound, for example. Or damage to your muscle tissue as a result of intense strength training. But as a bodybuilder you want your body to do more than ‘repair’ your muscle tissue. You want it to add some ‘extra’ muscle mass to those repairs. However, it only does that if your training meets the criteria for hypertrophy and your body therefore sees ‘reason’ to arm you for the next training (supercompensation) by means of extra muscle mass. In addition, you must provide your body with sufficient nutrients to be able to create that extra weapon arsenal: ensure that you eat more than you burn and that you get enough protein. A third condition for muscle growth is sufficient sleep, because sleep repairs muscle tissues and because protein synthesis is optimal during your sleep. And as you know, that protein synthesis is necessary to create ‘new’ muscle tissue i ] . Hence the often-heard credo ‘muscles grow in your sleep’.


Growth hormone, also often called Human Growth Hormone (HGH), is produced by the pituitary gland, especially during sleep. The peak is about two hours after falling asleep. Growth hormone is of great importance to bodybuilders for two reasons. Firstly because it promotes the protein synthesis process and thus the repair and growth of cells and tissues ii ] . Secondly, because growth hormone helps to regulate the body’s metabolism, including by stimulating the body to burn energy from fat reserves.

Growth hormone thus stimulates both muscle building and fat burning. In addition, it protects muscle tissue against breakdown during a calorie-restricted diet (the ‘cut‘, in bodybuilder terms). This is apparent from a study by the University of Chicago iii ] . Two groups of subjects were allowed to lose weight in exactly the same way for two weeks. One group got eight hours of sleep a day, and the other five hours. The few sleepers lost 55 percent less fat mass and 60 percent more lean body mass than the enough sleepers. The positive influence of sleep on fat burning is also shown by an epidemiological study from Case Western Reserve University in Cleveland iv ]. People who only sleep five hours a night become fat twice as quickly as those who get eight hours of sleep per day, according to that study.

Many bodybuilders separate the goals of muscle building and fat burning through ‘bulking‘ and ‘cutting‘. Legitimate, as far as we’re concerned, provided you do that bulking with policy (read: in moderation). From the foregoing you can conclude that sufficient sleep and therefore the production of growth hormone is of great importance in both processes:

  • when bulking to stimulate muscle growth and limit fat storage due to the calorie surplus;
  • when cutting to prevent muscle breakdown and stimulate fat burning.

The production of growth hormone also has other positive effects. It strengthens the bones and heart function, and regulates the amount of fluid in the body.

With all these benefits, it’s no wonder that synthetically produced growth hormone has become popular in the sports world. Fortunately, you can do enough to do without the synthetic variant. In addition to getting enough sleep, this means avoiding stress, not smoking and drinking, eating enough proteins and not consuming too many sugars. Doing a lot of cardio for a long time can also counteract the production of growth hormone.


Sleep promotes the production of yet another hormone associated with muscle building and fat loss: testosterone. We already knew that sleep and the level of testosterone levels are related from the fact that you produce significantly more testosterone at night than during the day v ] . And in principle, the more you sleep, the more testosterone you produce (especially during the first REM sleep vi ] ). For example, researchers at the National University of Singapore have calculated that for every extra hour of sleep, your testosterone levels rise by 13 percent vii ]. And a University of Chicago study once showed that men in their 40s could double their testosterone levels if they got more sleep viii ] . In this way they could even obtain the same testosterone levels as male in their twenties. So if you are a middle-aged man considering testosterone therapy, you might want to try improving your sleep quantity and quality first. Do not hesitate to use such a sleep app for this. Estimating how much you sleep is actually quite difficult.

So sleep is good for your testosterone levels. But to what extent is testosterone good for your bodybuilding goals (muscle building and fat loss)? After all, the obvious idea for many that ‘more testosterone = more muscle mass’ needs some nuance. It is true that the building of muscle mass can get a huge boost when testosterone levels are significantly increased. But usually it concerns unnaturally high levels, namely as a result of the use of anabolic steroids. Increasing your natural testosterone levels – for example by sleeping more, consuming certain foods and by doing strength training – has hardly any direct effect on muscle growth. At least that’s what we can deduce from a 2003 study by the Charles R. Drew University of Medicine and Science. ix] In summary, it showed that it makes little difference to muscle growth how high or low your testosterone levels are, as long as those levels are within the normal physiological range – 300 to 1000 nanograms per deciliter (ng/dl) in men x ] . Well, now it was a study conducted on non-strength training individuals. However, another 2012 study from Canada’s McMaster University, conducted among young men in training, came to a similar conclusion. Hormonal differences were found to have hardly any direct influence on the production of muscle mass, nor on the amount of strength (in this case with the leg press). This is because those differences were all within the normal physiological range [xi ] .

The foregoing probably explains why most strength athletes hardly notice so-called natural testosterone boostersIf  they ‘boost’ your testosterone levels at all (which in itself is quite possible), then that boost will never be big enough to effectively affect your muscle growth. Because your testosterone levels may rise, but stay within their natural range. Although we can imagine that older men whose testosterone levels are already naturally on the low side (which are close to 300 ng/dl), can also benefit from a natural ‘t-boost’ in terms of muscle growth.

All of this is by no means a plea for the use of anabolic steroids. Nor did we say that as a bodybuilder you do not benefit from naturally elevated testosterone levels. Well, as a teenager or twenties, whose t-levels are skyrocketing, you don’t really have to worry about your testosterone at all (let alone consider steroids!). For people in their thirties, forties and fifties, the benefits of naturally increased testosterone levels lie mainly in things such as a higher libido, more energy and less fat. Research by the Charles R. Drew University of Medicine and Science, just cited, shows that fluctuations in testosterone levels within the natural range do affect body fat percentage. For example, a reduction in a person’s testosterone value from 600 ng/dl to approximately 300 ng/dl resulted in an increase of no less than 36 percent in fat mass. Testosterone inhibits the formation of fat cells xii ] , while low testosterone levels contribute to obesity xiii ] , according to a 2011 meta-analysis .

The conclusion is that as a bodybuilder you benefit from high natural testosterone levels and that sufficient sleep makes an important contribution to this. Although the amount of testosterone, if present within the natural margins, usually does not have a direct influence on the production of muscle mass, the testosterone value does play a direct role in preventing the production of fat mass. In addition, higher testosterone levels, especially in older men, provide an overall more energetic feeling, which also has a positive influence on strength training.


A hormone value that bodybuilders want to keep as low as possible is that of cortisol. Cortisol is often referred to as a stress hormone because it is released during any form of stress, both physical and psychological. Thanks to cortisol, you can handle that stress better in the short term. But at the same time, it unleashes all kinds of negative ‘side effects’. A high cortisol value can be recognized by, among other things, general fatigue, negative mood, more need for sugars, increase in fat mass due to a delayed functioning of the thyroid gland, lowered libido, and all kinds of stomach and intestinal complaints. A long-term high cortisol level even promotes aging, brain damage and muscle breakdown. Because of the latter, we count cortisol among the catabolic (muscle-depleting) hormones, just like the female hormone oestrogen. The bodybuilding-cortisol relationship is nevertheless a somewhat complicated one. After all, intensive strength training also causes physical stress and therefore the release of cortisol. In strength training, cortisol is indispensable to replenish or retain fuel and/or to dampen inflammation. In this way, the catabolic cortisol also plays a positive role in the anabolic (muscle-building) process.

We do not want to elaborate on the (acute) role of cortisol in strength training in this article. When it comes to the negative effect of cortisol, we mean the effect of a prolonged elevated cortisol level. If you’re exposed to stress often and for a long time (stress other than the stress that strength training produces), that won’t help your goals as a bodybuilder.

Stress is unfortunately often unavoidable in everyday life. Fortunately, there is a very effective remedy for high cortisol levels: sleep. According to Shawn Talbott, biochemist and author of The Cortisol Connection (2002), when you sleep eight hours instead of six, your body’s cortisol levels can drop by 50 percent. xiv ] Too bad, a high cortisol value also has the unpleasant property that you fall asleep more difficult and/or sleep poorly. And so the remedy fails. It is because of this that people with insomnia often end up in a vicious circle.


Sleeping at night also has a direct effect on sugar levels. For example, on the sensitivity to insulin, the hormone your body produces to keep your blood sugar at a stable level. The less sensitive you are to insulin, the more fat your body stores. But the hormone also plays an important role in the muscle development process. When insulin binds to muscle cells, various biochemical reactions are triggered in the muscles. In turn, these reactions promote protein synthesis, essential for muscle growth. In addition, insulin helps to relax and widen blood vessels, increasing blood flow to the muscles.

A good night’s sleep promotes the body’s sensitivity to insulin. If you only sleep four hours during one night instead of 8.5, the sensitivity to insulin already decreases by almost a quarter, according to a study by the Leiden University Medical Center (LUMC) from 2010. xv ]


The duration of your sleep also affects your basal metabolic rate (or metabolism), i.e. how much energy you expend at rest. This is according to research on the link between sleep and T4 levels. T4 (or Thyroxine) is a prohormone produced and secreted by the thyroid gland. A deficiency of thyroid hormones results in a decreased metabolism, among other things. And reduced sleep reduces T4 levels xviii ] xviv ] .


We have already seen that sleep directly contributes to the reduction of fat mass in various ways: by producing growth hormone, by stimulating testosterone levels, by lowering cortisol levels and by promoting insulin sensitivity. But there’s another way sleep helps you keep your body fat in check: sleep curbs appetite. At least several studies exist xvishowing that calorie intake increases during the day as the amount of sleep decreases. The most logical explanation for this is that the duration of sleep affects the hormones that regulate hunger: ghrelin and leptin. At the same time, the burning of calories may decrease because you are less physically active during the day as a result of poor sleep. For the record: lying awake doesn’t burn any calories. Well go ahead, maybe a few, if you toss and turn a lot.

If you’re a young bodybuilder and you’re having an accident to cope with your raging metabolism, you won’t see an inhibited appetite as an advantage. But for older bodybuilders or bodybuilders with naturally slower metabolisms, this is another good reason to sleep like a baby.


A good night’s sleep also has direct positive effects on your training. Not only because you are well rested physically, but also mentally. During your sleep, your brain is recharged (your brain is, as it were, ‘washed’ xvii ] ). This allows you to be focused during the day. In your work, for example. Or during strength training. Mental recovery during sleep also benefits other mental aspects of training, such as motivation and mind-muscle connection.


Prolonged sleep is indispensable for muscle growth because it repairs muscle damage, takes care of a large part of the protein synthesis, produces growth hormone, lowers the cortisol value, increases insulin sensitivity and recharges the brain to be able to finish a training focused and motivated.

Nighttime sleep is also important for keeping or reducing your body fat percentage, namely because of the promotion of growth hormone and testosterone, lowering the cortisol value, increasing insulin sensitivity, maintaining the metabolism and inhibiting the appetite. Researchers from the University of Leeds recently concluded that three hours less sleep means three centimeters more around your waist xviv ] .


It should be clear by now that sleep is just as important for a bodybuilder as training and eating right. It is therefore a shame if you neglect this crucial aspect of muscle growth and fat burning. It is remarkable that this happens very often, while sleeping is just so nice! But in our busy, hectic and often stressful existence, good, long-lasting sleep is unfortunately not a matter of course for many.

Finally, some notes and tips:

  • An open door perhaps, but still: don’t train right before going to sleep. Your body is still too active, too ‘awake’ in the hours after your workout.
  • Another open door: not everyone needs the same amount of sleep. But man’s average sleep requirement is between seven and nine hours. That of a fanatic (strength) athlete is probably even higher.
  • To find out how long you should sleep in your case, the next time you have a few days off, go to bed when you’re tired and sleep through until you wake up on your own.
  • Try downloading a sleep app to see how much sleep you are currently getting. Or as an aid to get a better sleep rhythm.
  • No matter how good sleep is, with the passing of the nighttime hours, your body gradually enters a catabolic (muscle-depleting) state. The fuel, which is necessary for all body processes during sleep, is running out. Now you don’t have to immediately panic about it and even set the alarm clock at night to ‘have something to eat’. However, there are scientifically substantiated arguments to consume slow proteins just before going to sleep. A casein shake for example, or a cup of (skimmed) cottage cheese.
  • A common misconception is that rest can compensate for a lack of sleep. However, sleep goes much further than a ‘normal’ state of rest. In your sleep, your consciousness and senses are virtually switched off and you do not react to external stimuli, unless they are so strong that they wake you from your sleep.
  • Even a number of short naps cannot replace one long sleep. It is mainly in your deep sleep that your body starts its ‘rejuvenation course’ and your immune system, central nervous system and your tissues come to rest and go into recovery mode.
  • Do you have a hard time falling asleep? Then make sure to exercise more during the day. Being active in sunlight also improves the quality of your sleep.


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