Sleep & Performance
We spend about a third of our lives asleep. Why?…..
We used to believe that we slept to save energy during the night, as it was too dark to hunt. In fact the amount of energy saved by sleeping is tiny and recent research shows that far from being in active, sleep actually plays a hugely important role in brain development, is essential for the maintenance of normal cognitive skills such as speech, memory and flexible thinking and is needed for normal body growth, development and repair. In other words sleep is vital for performance.
The science of sleep
Our sleep is divided into two main types: REM (standing for Rapid Eye Movement) and non-REM (which is further split into four stages).
Stage one is the beginning of the sleep cycle, is a relatively light stage of sleep and can be considered as a transition period between wakefulness and deep sleep. During stage one, the brain produces very slow high amplitude brain waves (theta waves), muscle activity slows right down and slight twitching can occur. If you wake someone during this stage, they might insist that they weren’t really asleep. Stage one lasts around 5-10 minutes.
Stage two is also known as ‘True Sleep’ and lasts for approximately 20 minutes. The brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. The breathing pattern and heart rate start to slow down and body temperature decreases. This period accounts for the largest part of human sleep and is associated with the processing of short into long term memory. If you dream during stage two sleep the dreams are in black and white.
Stage three (deep sleep) was previously divided into stages three and four but is now counted as a single stage. The brain begins to produce delta waves, that are high amplitude (large) and low frequency (slow). Breathing and heart rate are at their lowest levels, breathing is rhythmic and there is limited muscle activity. If you wake someone during deep sleep they do not adjust immediately and often feel groggy and disoriented. Bedwetting, night terrors and sleepwalking are part of stage 3. There is also a surge of growth hormone production which is associated with growth and muscle repair.
The first rapid eye movement (REM) period usually begins about 70 to 90 minutes after falling asleep and there are between three and five periods of REM sleep a night. Although we are not conscious during REM sleep, the brain is very active, often more active than when we are awake. This is the period when most dreams occur. Our eyes dart around (hence rapid eye movement), our breathing rate and blood pressure rise. However, while the brain and other body systems are very active, the voluntary muscles become paralysed and relaxed. This is thought to have evolved to stop us from acting out our dreams. REM sleep is also known as active or paradoxical sleep. The first cycle of REM sleep might last only a short amount of time, but each cycle becomes longer and can last up to an hour as sleep progresses. REM sleep in thought to be important in putting things into perspective.
After REM sleep, the whole cycle begins again, although it does not necessarily progress through the stages in sequence. Sleep always begins in stage 1 and initially progresses into stages 2, and 3 but after stage 3 sleep, stage 2 sleep is usually repeated before entering REM sleep. Early in the night stages 3 and 4 of non-REM sleep dominate while later in the night stage 2 and REM sleep are more common.
Sleep and Performance
Restricting sleep has been shown to impair athletic (1) and cognitive performance (2) as well as effecting mood (3), glucose metabolism (4), appetite regulation (5), and immune function (6) and increasing blood pressure (7) and stress (8).
Slow wave or deep sleep consistent with stage 3 is known to be important for recovery in athletes, with increased growth hormone release giving optimum conditions for growth and development of muscle tissue. In 1981 Shapiro et al. investigated sleep prior to and following a 92 km marathon and found that both total sleep time and the amount of time spent in stage 3 increased significantly in the four nights after running, suggesting a greater need for repair after an endurance event (9).
There have been a wide variety of studies looking at sleep deprivation and sports performance. Results show that structural performance is only significantly damaged after 24-30hrs without sleep but that mood, motivation, cognition and reaction times may be effected after much less time, particularly if the tasks require repetition or precision. Women would appear to be slightly less physically effected by lack of sleep but have longer recovery times and teenagers appear to be more vulnerable to the effects of sleep deprivation than adults (1).
Total sleep deprivation is not common in real life situations but loosing 2 or 3 hours a night is. The general recommendation for adults is to aim for 8hours sleep a night (adolescents 9-10hrs) but surveys of sleep habits generally show that most people get around 6.5-7.5hr. Elite athletes average a little higher but a number of studies have suggested that athletes could benefit from more sleep. In 2011 Mah et al. tracked the Stanford University basketball team for six month during which time she added an average of almost two hours of sleep to their night. As a result players increased their speed by 5%, their free throws were 9% more accurate, they had faster reflexes and felt happier (10). Other studies have shown similar benefits for football and tennis players as well as track athletes and swimmers (11).
For elite sport is may also be interesting to note that one effect of sleep shortage appears to be a reduced ability to correctly assess your own performance, possibly reducing coachability. In addition there is also strong evidence that sleep deprived individuals are much more likely to remember negative information than positive or neutral, potentially making their response to coaching more difficult (2)
Many athletes report worse sleep in the nights prior to important competitions. A study of elite Australian athletes showed 64.0% indicated worse sleep in the nights prior to an important competition, 82.1% reporting problems falling asleep (12).
Cognitive performance is effected by shortage of sleep in two district ways, by both reducing alertness and attention and effecting the speed and accuracy of cognitive processing (2,13).
ATTENTION & WORKING MEMORY
Possibly the most widely studied area is the effect of sleep deprivation on attention and short term or working memory. As little as one night of poor sleep has been shown to affect vigilance, auditory and visuospatial attention and reaction times. However, not all the studies have been conclusive and the type of task and the circumstances appears to be very important (13). Most studies show that there is less effect on familiar or automatic tasks, but that those which are tricky and need greater coordination between different parts of the brain can be severely inhibited. There is also evidence that even moderate sleep deprivation can have a much more serious effect on younger people, particularly during adolescence (2).
LONG TERM MEMORY
The processes involved in memory are hugely complicated but it is understood that when new memories are made, they are first stored as an ‘experience’ within the brain. For them to persist over a longer time, the brain needs to convert or consolidate them making the memories more resistance to decay and allowing recollection (14). Sleep and particular stage two of non-rem sleep, has been implicated in both the encoding and consolidation of memory and the amount of post-training activation in various parts of the brain during stage two, has been found to be directly proportional to next day task improvement (2).
Research has shown that after learning information, sleep is more beneficial to accurate recall, than a the same time period spent awake and that complicated layered tasks are better learnt over a series of days with sleep in between than over a single day (13).
Research into the effects of sleep deprivation on cognition have consistently found that people struggle to form new long term memories when they have not had enough sleep and the recall of simple details can be reduced by up to 40% (2). Studies in young people have shown that even moderate sleep deprivation can have a hugely detrimental effect on the total recall of information, but may have a far lower effect on answering multiple choice style questions, where there are cues in the question to aid recall (13).
As well as strengthening the memory of individual bits of information, there is also evidence that sleep enhances the linkages between different pieces of learnt information and hugely enhances problem solving. In 2004 Wagner et al looked at the effect of sleep on mathematical problems and found that not only were those that had slept between trial and retrial 16.5% faster than those that had not, but 60% also found short-cuts for solving the problems more efficiently (15).
Sleep and Emotional Intelligence
As mentioned under athletic performance, sleep deprivation has been shown to promote negative mood and memory and there is a also a bank of research that shows that sleep deprivation causes an increase in irrational emotional behaviour. Brain studies have shown evidence that a good nights sleep acts to reset the brains reactivity to next-day emotional challenges and promotes appropriate behavioural response to external events (2).
Although everyone is different, most of the evidence from a wide variety of studies suggests that we should get between 7 and 10 hours of sleep a night, with athletes and adolescents aiming for the higher end of that range (16). Sleep loss has also been shown to be cumulative, and repeated loss of as little as an hour a night has been shown to have an effect on both athletic and academic performance (13).
It has also been found that in the general population it is best if 80-90% of sleep is taken in one block and at night. Napping may improve short-term performance but may also disrupt normal sleep patterns, fragmenting sleep and increasing the number of times you wake during the night. The exception may be in athletes where napping has been shown to aid recovery. If naps are taken, it is recommended that they are not after 4pm as this has the biggest impact on sleep.
If you are unsure about whether you are getting enough sleep, the BBC Science website has a sleep profiling program that you may find helpful.
Boosting Sleep and Performance with Nutrition
If you are interested in how you can boost the quality and quantity of sleep and so performance using nutrition, there is some really interesting new research. I will be writing about this soon but if you would like more information please contact me and I would be delighted to help.
REFERENCES & FURTHER READING
1. Halson 2013. Sleep and the Elite Athlete. Sports Science Exchange 26(113), 1-4
2.Walker 2009. The Role of Sleep in Cognition and Emotion. The Year in Cognitive Neurosciene. Ann N.Y Avad Sci 1156, 168-197
3. Belenky G, Wesensten NJ, Thorne DR, et al. Patterns of per- formance degradation and restoration during sleep restriction and subsequent recovery: a sleep dose–response study. J Sleep Res. 2003;12(1):1–12.
4. Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet. 1999;354(9188): 1435–9.
5. Spiegel K, Tasali E, Penev P, et al. Brief communication: sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med. 2004;141(11):846–50.
6. Krueger JM, Majde JA, Rector DM. Cytokines in immune function and sleep regulation. Handbook Clin Neurol. 2011;98: 229–40.
7. Ogawa et al 2003. Total sleep deprivation elevates blood pressure through arterial baroreflex resetting : a study with microneurographic technique. SLEEP 26(8). 986-989
8. Spiegel et al 1999. Impact of sleep debt on metabolic and endocrine function. The Lancet. 354(9188), 1435-1439
9. Shapiro 1981, Sleep and the athlete. Br J Sports Med 1981;15:51-55 doi:10.1136/bjsm.15.1.51
10. Mah et al 2011. The effects of sleep extension on the athletic performance of collegiate basketball players. Sleep 34(7). 943-50
11. Summery of Cheri Mahs work on Stanford athletes http://scopeblog.stanford.edu/2013/09/26/ask-stanford-med-cheri-mah-responds-to-questions-on-sleep-and-athletic-performance/
12. Juliff et al 2014. Understanding sleep disturbance in athletes prior to important competitions. J Sci Med Sport 2014 Feb 13.
13. Alhola and Polo-Kantola 2007. Sleep deprivation : Impact on cognitive performance. Neuropsychiatric Disease and Treatment 3(5), 553-567
14. Walker 2005. A refined model of sleep and the time course of memory formation. Behav Brain Science 28, 51-64
15. Wagner 2004. Sleep inspires insight. Nature 427, 352-355
16. Van Dongen et al. The cumulative cost of additional wakefulness: dose–response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep. 2003;26(2): 117–26
I would also like to thank Prof Jason Ellis for his inspiring talk at the SENr conference in June 2014.