When we have multiple deadlines coming up, feel horribly under-prepared and realise how much work we have left.
Want to watch ‘one more episode on Netflix’.
Want to go out for a few drinks with friends, but know we have to be up at 6am the next day.
What do we sacrifice first to make time for all of our plans?
Feeling run down and tired?
Not hitting the numbers, we want in the gym?
Seem to pick up every cold or bug that is going round?
Where is the last place we look for ways to improve our recovery and performance?
The answer to both questions, of course, is sleep.
As a particularly ironic example, it’s currently 4:00am and here I am- staring gormlessly at my laptop, trying to get a few hundred words on paper before I start work.
The thing is, we all know how beneficial sleep is for performance and recovery.
But do we actually know how much our sleep habits affect us?
By and large, we all underestimate the power of sleep. Last year, the Centre for Disease Control and Prevention in the US reported that 33% of Americans do not get enough sleep. Another report suggests that the worldwide economic cost of sleep deprivation is $411 billion.
If we all think back, we can all remember a time where we have barely slept, and our performance the next day has suffered. At school, work, the gym, the track- wherever it is, we struggle to perform optimally when we are sleep-deprived.
As well as thousands of anecdotes from parents of new-born babies, the negative effects of sleep-deprivation have been widely reported in scientific research.
Sleep deprivation is the acute or chronic loss of sleep. In most research, participants are kept awake for 24-72 hours without sleep. However, in real life, ‘chronic partial sleep deprivation’ is more common- where we sleep for a limited period of time (less than 5 hours per night) for successive nights.
Effects of sleep deprivation on cognitive performance
The effect of sleep deprivation on several factors of cognitive performance has been researched, with a focus on changes in attention and memory following sleep deprivation. Both attention and memory have two aspects to performance- speed and accuracy. Research suggests that if we increase one, the other one will be affected- for example, if we drastically increase the speed of the task, it will not be done as accurately. Some research suggests that speed, but not accuracy, is worse with sleep deprivation (De Gennaro et al 2001). Other research suggests that sleep deprivation will not affect speed, but we will not be able to work with the same accuracy (Kim et al 2001). Regardless, it is clear that missing out on sleep will reduce our attention-span and working memory.
Other aspects of cognitive function that might take a hit include word memory (Drummond et al 2000), decision-making (Kilgore et al 2006) and logical reasoning (McCarthy and Walters 1997).
The evidence that sleep is important for everyday cognitive function is pretty clear- if you’re thinking about staying up late to finish that presentation, your decision-making the next day might not be as good. Missing out on sleep to cram some revision in for exams? Your ability to remember key words and arguments will be affected.
Getting up early to write an article on the effects of sleep deprivation?
You get the point…
Effects of sleep deprivation on physical performance
Sleep duration and intensity is certainly an important issue for athletes, and those looking to maximise their physical performance. A study on South African athletes suggests that 75% slept for less than the recommended eight hours. In another study, 70% of athletes reported sleeping worse in the night before competition than they usually would.
Missing out on sleep could even be the difference between success and failure. A study on 576 Brazilian athletes investigated sleep quality prior to a national or international competition. They showed that sleep quality was a predictor of performance, and those with poor sleep quality did not perform as well in competition (Brandt et al 2017). This is supported by research in netball players that showed the top two teams in a tournament had greater sleep quality and sleep duration (Juliff et al 2017).
The physical components of performance that are affected by sleep will vary, depending on the physical requirements of the sport, event or activity.
Effect of sleep deprivation on endurance performance
Studies show that just one night of sleep loss can decrease the time to exhaustion during an endurance running task (Azboy et al 2009). In these events, sleep deprivation is believed to have an effect through changes in perceived effort- that is, that exercise at a given intensity ‘feels harder’. A study by Oliver et al (2009) asked participants to run on a treadmill for 30 minutes after normal sleep, or 30 hours without sleep. The sleep deprived group covered less distance, although there was no difference in any physiological markers- suggesting that participants performed worse because it felt more challenging.
The negative effects on endurance events could be due to changes in the fuels we use for exercise. Pre-exercise glycogen stores were shown to be decreased after sleep deprivation, which may lead to decreased glycogen stores and reduced endurance performance. (Skein et al 2011). It appears clear that those who fail to get sufficient sleep before an endurance task will not be able to perform at their best.
Effects of sleep deprivation on explosive sports
The effects of sleep deprivation on sprint or explosive sports is less clear. A study in US collegiate weightlifters showed no difference in snatch, clean and jerk, front squat and total volume or intensity when deprived of sleep for 24 hours, despite negative changes in mood. However, one rep max bench press, leg press and deadlift were all decreased after three nights of sleep deprivation (Reilly et al 1994). This could be due to the different lifting tests used, or the longer duration of sleep deprivation.
Research on sprint performance is also unclear. Skein et al (2011) found slower average sprint times in male athletes running repeated sprints, however performance in 40m sprints has been shown to be unaffected after 64 hours of sleep deprivation (Takeuchi et al 1985). Interestingly, when basketball players were asked to extend their sleep by 2 hours per night for 5-7 weeks, they found improvements in sprint times, as well as ratings of fatigue in games and training (Mah et al 2011).
Although it isn’t clear whether sprint exercise is directly affected by poor sleep, sleep should be prioritised to reduce the risk of other negative effects on recovery, mood and cognition.
Sleep deprivation and recovery
There isn’t a lot of research on the impact of missed sleep on recovery from exercise, and the little evidence there is suggests that if we don’t snooze, we suffer. Increased pain perception and decreased emotional well-being have been reported after repeated nights of sleep deprivation (Haack and Mullington 2005). In the study on volleyball players, players deprived of sleep for a second night performed 4% worse than if they had sufficient sleep, suggesting that their recovery may have been affected (Azboy et al 2009).
Although there isn’t a lot of data on recovery and sleep, there is evidence that the physiological functions that regulate our recovery are impaired when we miss out on sleep. Lack of sleep can lead to a rise in catabolic (breakdown) hormones such as cortisol, as well as reductions in anabolic (growth) hormones such as testosterone and IGF-1, which may reduce protein synthesis and impair muscle recovery post-exercise.
Sleep deprivation can also change the response of hormones such as adrenaline, noradrenaline and serotonin- this leads to changes in the stress response that are similar to those seen in individuals with mood disorders. Chronic sleep deprivation may also affect glucose metabolism, appetite, food intake, protein synthesis, which are all factors that will impact our ability to recover and fuel optimally for future sessions.
Missing out on sleep is very likely to affect our ability to perform and recover- how much sleep we need, how much we can miss and get away with it, and how much our performance is affected is likely very individual. Evidence suggests that aspects of cognitive and physical performance are affected if we don’t get the required sleep, as well as changes in immune function, blood pressure and digestion.
Needless to say, if your performance has suffered recently, or you’ve struggled to recover between sessions, getting more shut-eye should be top of your list of priorities.
About the Author
Charlie is the owner of CB Nutrition, and has an MSc in Sport and Exercise Nutrition from Loughborough University. He supports athletes in several sports including canoeing, boxing, cricket, rugby league, and Olympic weightlifting.
To find out more about Charlie's work, check out:
Twitter: @Charlie Beestone
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