Healthy eating and a demanding workout do not bring the expected results without something very simple, but not always easy to achieve: a good night’s sleep. Although training stimulates growth, it is in the recovery period that this actually happens.
Unfortunately, many athletes do not sleep enough or do not sleep quality  because of factors that disturb sleep or simply because they are unaware of the influence of sleep on the process of muscle development.
What happens during sleep?
1. Protein synthesis and tissue regeneration
During sleep, protein synthesis increases, repairing damaged muscle fibers and building new tissues. This process, in addition to replacing worn out muscle tissue, also adds a new layer of lean mass. Therefore, in the end, the body regenerates and even increases its muscular volume .
2. Growth hormone release
Growth hormone plays an important role in protein synthesis and increase lean mass and muscle volume . Although weight-lifting training helps release growth hormone into the bloodstream , the greatest increase in hormone levels occurs during sleep .
3. Decrease in cortisol levels
Cortisol is a catabolic hormone, which increases muscle breakdown and inhibits its synthesis . Although their levels vary according to the circadian cycle, studies have shown that sleep alone decreases cortisol levels irrespective of the time of day 1 6. Levels decline even after a nap [1, 6], and even studies have shown that napping throughout the day improves performance in sleep deprived athletes .
Since cortisol levels are lower during sleep, this is a phase that we should take advantage of to promote muscle mass synthesis.
Consequences of sleep deprivation
There are several health problems associated with sleep deprivation . These include increased blood pressure, hyperglycemia (excess blood sugar), insulin resistance, and the risk of developing Type 2 diabetes. They are serious consequences for the general well-being and should not be overlooked. As far as sport is concerned, other problems can result from lack of adequate sleep.
Recent evidence suggests that sleep deprivation can have significant effects on performance, learning, memory, cognition, perception of pain, immunity and inflammation . In addition, changes in glucose metabolism and neuroendocrine function as a result of sleep deprivation may result in alterations in carbohydrate metabolism, appetite, food intake and protein synthesis, which may negatively influence the state nutritional, metabolic and endocrine levels of an athlete and potentially reduce their performance. 
1. Increased levels of cortisol
One of the main problems of sleep deprivation is the increased levels of cortisol [4, 7], which, in turn, increases muscle breakdown and decreases its synthesis . Another factor that increases cortisol levels is stress . Thus, decreasing stress and having a good quality and quantity of sleep are key to muscle growth.
2. Decreased levels of growth hormone
In conditions of sleep deprivation, growth hormone levels fall , which may hinder muscle growth, where this hormone plays an important role .
3. Decrease in testosterone levels
Testosterone is an anabolic hormone, meaning it increases muscle synthesis [4,5]. Studies have shown lower levels of testosterone in subjects with poor sleep quality or quantity .
4. Risk of injury and illness
Failing to sleep well or enough affects mental concentration, which can decrease an athlete’s performance and increase the risk of injury . In addition, it further affects the immune system and increases inflammation, which increases the risk of disease .
5. Increased body fat
Leptin and ghrelin are hormones that regulate appetite, with leptin having an inhibitory effect and ghrelin stimulating action. Several studies have shown that sleep deprivation lowers leptin and increases ghrelin, resulting in an increase in appetite, especially for carbohydrate-rich foods .
Growth hormone has a recognized role in body composition, not only in muscle synthesis but also in body fat degradation , so if it decreases with sleep deprivation, this can be reflected in an increase in body fat . In addition, elevated cortisol is also associated with an increase in body fat , which may occur due to sleep deprivation.
Nutrition to improve sleep
Although the sleep period has an anabolic potential, it can become highly catabolic if the body has to use proteins and amino acids as an energy source. To counteract this unwanted effect, it is necessary to maximize the anabolic potential of sleep, which can be achieved through adequate pre-sleep nutrition with food or supplements .