Sleep is important. I don’t think anyone would argue this. I personally feel the lack of sufficient sleep immediately. I get grumpy really easily, I can’t concentrate, my physical performance ability decreases significantly, I make more mistakes, I am also more unfriendly and can’t deal very well with any problems or complaints. In contrast, I take things really personally – and rather feel like crying than actually solving it. I guess all of us have experienced situations like this once before. As said, sleep is undoubtedly important. This is the reason why we decided to dedicate a blog post to it – with the aim to scientifically work up the effects of a lack of sleep as well as how much sleep we actually need.
Before we explain these details, we want to clarify the difference between sleep restriction and sleep deprivation. Sleep restriction means a disturbance of your habitual sleep-wake cycle. For example sleep restriction happens if you cannot fall asleep for a few hours, be awake for some hours during the night or wake up much earlier than usual. Sleep deprivation is an extrem case of sleep loss whenever you don’t sleep for a prolonged time, e.g. a whole night.
Multiple scientific studies have proven that a lack of sleep can have multiple negative effects on our body and physical performance:
Short time sleep restriction can impair concentration, decrease patience, and lower motivation as well as increase irritability. (Foster & Wolff, 2005)
Long time sleep restriction can even increase the cortisol level about 50% (Maderthaner, 2008).
Sleep restriction can also lead to a slower and less accurate cognitive performance: e.g. staying up for more than 27 hours will decreases our cognition similar to a drunk person with ~0,85 per mille. (Foster & Wolff, 2005)
Chronic sleep reduction can also lead to immune-suppression.
Moreover, the length of sleep negatively correlates with the degree of obesity (Atkinson, & Davenne, 2007).
Reducing the quality and quantity of our sleep can cause an imbalance in the autonomic nervous system, similar to symptoms of the overtraining syndrome.
How much sleep do we actually need?
The National Sleep Foundation recommends 7–9 hours of sleep each night for a healthy sleep but the number has fallen since the mid-twentieth century. Some studies recommend athletes to sleep between 9 and 10 hours on a daily basis. The suggested hours of sleep before a competition vary a lot since numerous other factors, such as nervousness, anxiety, etc. can also impair our performance.
Some studies exclude gross motor performances (e.g. walking, running or walking upstairs) and some maximal physical efforts from being negatively effected of a lack of sleep and stress. This means that there is no significant negative effect of sleep loss on whole body movements, where large muscle groups are used. Whereas sport specific performance, which requires high neurocognitive reliance, is more prone of being negatively effected by a lack of sleep. This means in sports where attention, decision making, and working memory is important are more vulnerable to be effected by sleep (e.g. soccer, tennis, climbing…).
Some studies have shown an increased perception of effort after sleep loss which is leading to a reduced power output. Moreover a few studies suggest that grip strength performance won’t be diminished after sleep loss.
The negative effect of bad sleep on our mood state
It is known that bad/a lack of sleep can cause poor mood state. Specifically, it can lead to decreased vitality and energy, but increase depression, sleepiness, and confusion which can be the reason of decreased motivation after sleep restriction.
Our brain is very active during sleep. Sleep can therefore be defined more as an active than a passive process.
It is proven that a good quality and quantity of sleep are essential for athletes because of the restorative effect on the immune and the endocrine (hormonal) systems, as well as the increasing recovery of the nervous and metabolic cost. If you recover faster or better, you can train more or at least feel fresher and are able to train harder within a shorter break. Moreover, it enhances motor task learning, cognitive development like learning and memory and is also vital for synaptic plasticity. This means, if an athlete wants to learn a new technique or movement, sleep will help to do so on a cognitive and physical level. What is synaptic plasticity? If you don’t use a type of muscle, synapses will get weak in this area. Whenever you use a specific muscle, the synapses are active more often and your new movement will get better and requires less effort.
Good sleep is supposed to be critical for tissue regeneration and growth through the release of anabolic/growth hormones. These hormones increase the synthesis of proteins and mobilise free fatty acids to provide energy which, in turn, will support the healing process of muscle damage due to a tissue building and muscle growing effect. Muscle damage happens whenever you have trained and your muscles are sore.