Essay: What is sleep and is it important for athletic performance?

We’re teaching our players: Sleep is a weapon. ~ Sam Ramsden, Director of Player Health and Performance, Seattle Seahawks

Abstract

Overview of the project

This review was undertaken to understand what sleep is, its function and to explore its role in athletic performance. Good sleep, balanced nutrition and regular exercise are the three pillars for a healthy life. The latest report by the Royal Society for Public Health called “Waking up to the health benefits of sleep” tells us that many of us lack good quality sleep with numerous deleterious consequences including road traffic accidents, mood disorders, cardiovascular disease, obesity and diabetes. Adolescent athletes like me are particularly sleep deprived as physiologically we sleep later (made worse by social media), have to get up for school early but should have 9 hours sleep yet may get only 6-7. The best athletes in the world sleep, a lot! Sleep extension will not make most athletes world-beaters but it will improve tiredness, illness, concentration, speed, cognitive skills, memory improvement, fatigue and mood.

Summary of main findings

• Most people don’t get enough sleep, no potion or pill can replace it.
• Less sleep slows speed, reaction times, endurance and impairs mood and cognitive function
• Sleeping longer and napping improve speed, reaction times, sub- maximal exercise (endurance), mood , fatigue and perception of exertion and maybe a longer playing career with fewer injuries.
• Extend sleep time for weeks rather than days to get the most benefit.

Implications for Future Research

More sports specific work needs to be done, with randomised controlled trials and with more objective data from standardised tests to find the optimal sleep time for individual athletes and maximising its quality. The effects of extending sleep over normal levels are unknown.

Introduction

“Sleep is extremely important to me – I need to rest and recover in order for the training I do to be absorbed by my body” ~ Usain Bolt.

If the fastest man in the world sleeps for 9-10 hours, LeBron James one of the best basketball players in the world and Roger Federer (arguably the best tennis player ever) both sleep for 12 hours a day, then there must be a good reason.(see appendix)

I’m a student in the sixth form but I am also a keen soccer and rugby player. I know that a players and teams performance is partly due to intrinsic ability, training, coaching, nutrition and motivation. (see appendix)

We all sleep but it has remained to me a bit of a mystery.

Sleep has previously been described as something that is of the brain, by the brain and for the brain.But what exactly is it and how does it affect the rest of the body and especially athletic performance.

A recent report by the Royal Society of Public Health called “Waking up to the health benefits of sleep” concluded “ sleep is as vital for survival and health as food and water. Sleep is involuntary and inevitable”. Poor sleep is linked to depression, insomnia, high blood pressure, cancer, workplace and road traffic accidents, poor exam results, adult onset diabetes and obesity. Four in ten people feel they aren’t getting enough sleep and one in five people sleep poorly most nights (the most common health complaint after pain!). One in ten people take a drug to help them sleep and 10 million prescriptions for sleeping pills are written in England every year!

The question I will try to address is does sleep really matter to how athletes perform? Many top football clubs eg Real Madrid and NFL American football teams now employ sleep consultants to assess and optimise their teams sleep patterns in order to get the best out of their performances as ‘marginal gains’ (Dave Brailsford former head of British cycling) can make the difference between winning and losing and a good or bad season.

I’m going to describe sleep, its functions, how sleep in athletes is currently analysed in athletes and what happens when we don’t get enough good quality sleep, and the causes.. I am then going to present the study evidence which will show the important benefits of improving sleep and how this improves athletic performance in terms of mood, reaction times, speed, power and decision making..

Research methods

I conducted an Internet search using Google, Google scholar and PubMed search engines. I used varying combinations of the following terms; sleep, function, assessment, analysis, athlete, athletic performance, exercise, injury, deprivation, fatigue, extension, recovery. When I found appropriate paper I then followed the citation index for that paper to find further similar papers. I also looked at the websites of the National Sleep Foundation, the Royal Society for Public Health, the BBC and Fatigue Science and the Gatorade Sport Science Institute. When I typed sleep into the websites of sport Wales and sport England and team GB nothing came up. There was a lack of standardisation in a lot of the studies and a mixture of subjective and objective data sometimes making it difficult to compare them or draw unequivocal conclusions.

Aim 1: To define Sleep

Objective 1.1: To describe the structure and function of normal sleep in athletes

Structure

Sleep is a reversible state of behaviour where the individual is usually lying down, unresponsive and disengaged from the surrounding environment . It happens every 24 hours (circadian rhythm) and the urge to sleep increases the longer we are awake (sleep homeostasis). There are essentially three states in the sleep /wake cycle. They are awake, non rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). NREM and REM are identified by a special test called polysomnography which uses electrodes attached to your head and body. Sleep is generally entered via NREM which has three stages (1 to 3) with stage 1 and 2 being light sleep and stage 3 being deep (slow wave) sleep. After about 70-90 minutes the brain changes from NREM to REM sleep, which is characterised by dreaming, rapid eye movements and lack of muscle tone (except the eyes and diaphragm).

The brain goes through roughly 5 cycles of NREM/REM sleep with occasional brief awakenings each night of sleep, with each cycle lasting roughly 90 minutes. Deep NREM sleep happens earlier in the night and sleep periods of REM get a bit longer towards the latter part of the night.

It can be affected by both internal and external factors including genetic traits, light, noise, nutrition, exercise, age, medications, jet lag, emotion and many medical disorders.

Subjective measurements of sleep duration have changed a lot over the last 70 years. From 8-9 hours in 1959 to 7-8 hours in 1980 and in an American survey in 2013 it was down to between 6.5 and 7.5 hours. The National Sleep Foundation in the USA recommends between 7 -9 hours for healthy sleep. This reduction is almost certainly due the influence of artificial light both indirectly in allowing longer days of work and relaxation and via technology more recently via viewable technology that is both arousing and suppresses the production of melatonin which is a sleep onset regulating hormone.

Function

Sleep is vital for cognitive and physiological function; it has restorative effects on the immune and endocrine systems and is important for both learning and memory of both physical and mental tasks.

Slow wave (deep) sleep is important for recovery for athletes and increases in proportion to the duration of preceding wakefulness..Growth hormone is produced maximally during slow wave sleep, this suggests it may be the period when anabolic and muscle repair occurs. If slow wave sleep is reduced by sleep deprivation then daytime sleepiness increases and performance reductions have been noted . Subsequent sleep periods have more slow wave sleep in proportion to the duration of preceding wakefulness and this was demonstrated in recovery sleep in athletes after running a 92k marathon.

The function of REM (or dream) sleep is not entirely clear but is felt to help memory formation and consolidation. Several studies have shown improvements in motor task tests after a night of sleep but not in people having the same amount of time awake, though this has not been tested in athletes.

Objective1.2: To discover how we analyse sleep in athletes.

When analysing an athlete’s sleep we want to assess 3 main areas; the duration of sleep, the quality of sleep and the circadian timing of that sleep (i.e. at what time of day does it occur).

Quality is hard to define but is probably best thought of as a persons satisfaction with their sleep and objectively as how easy it is to initiate and how uninterrupted it is.

The first thing we want to assess is what sleep chronotype the athlete belongs to. At one end of the spectrum we have early chronotypes who go to bed early and get up early, at the other end we have late chronotypes who go to bed late and wake later on the morning, which interestingly is a pattern that is physiologically normal in teenagers ( though made worse by smartphones and laptops).It is important to know this as if training or competition occurs when your circadian rhythm thinks you should be asleep then your body and your mind may not be as receptive to exercise.

It is useful to get a general history of the individual’s daily activities, including bedtime, morning wake times, training schedules, game schedules, caffeine, alcohol and other medication history. It is important to find out about the regularity of sleep routines and duration as well as daytime naps. Use of laptops, smartphones and other light exposure and its timing is also useful. Enquiry regarding mood, general health, snoring, sleepwalking, sleep talking and nightmares may also be significant when investigating an individual’s sleep pattern. If any significant problems are found then the athlete may need to see a sleep specialist – there are 6 main groups of sleep disorders; insomnia, sleep-related breathing disorders, sleep-wake disorders, hypersomnolence, sleep-related motor disorders and parasomnias.

There are a few different ways to formally assess athletes sleep patterns; the first is asking the individual to fill out a 2-week sleep diary, noting all the above occurrences. It can help to identify sleep patterns and poor sleep hygiene (for example drinking caffeine or alcohol close to bedtime, having a noisy bedroom environment). It will help to get a guide to the athlete’s perception of their sleep pattern both when training and around game/competitions. Sleep diaries are subjective so it does rely on the athlete to fill it in correctly and not forget. Sleep diaries can overestimate sleep time by more than an hour when compared to objective measures such as wrist actigraphy.

Objective sleep pattern time is generally gathered from wrist actigraphy which is a watch type instrument that measures movement and light and has been validated against the gold standard of sleep measurement which is polysomnography with reasonable accuracy provided it is set up correctly. Actigraphy is able to collect data wherever the athlete is, over a long period of time (up to and beyond 2 weeks) and it is waterproof and shockproof. Its main disadvantage is that it does not detect brain activity which means it can overestimate sleep (eg if lying in bed still) or underestimate sleep (e.g. if small movements during sleep).

Chronotype is estimated using a type of computerised questionnaire such as the Munich Chronotype questionnaire or morningness-eveningness questionnaire though none is as accurate as measuring the onset of production of sleep promoting hormone melatonin but this is time consuming and complicated .

Polysomnography is the gold standard for measuring actual sleep. It is performed in a hospital or laboratory setting due to the equipment and personnel required to conduct the test. It consists of a series of electrodes placed around the athlete’s head, chest, abdomen and legs. They measure brain waves, eye movements, leg movements, heart rate and rhythm, oxygen levels and breathing patterns. It is often combined with video and sound recording and to look for abnormal sounds and movements. It is used to diagnose sleep disorders but with all the complex wiring is not so easy to get a good picture of someone\’s sleep pattern over several days in their normal lives.

Aim 2: To identify what happens when sleep goes wrong in athletes

Objective 2.1: To explore the nature of sleep in athletes and what disturbs it.

Some authors feel athletes should sleep for 9-10 hours to allow for adequate recovery from training and competition but a study of elite South African athletes has shown they sleep 6-8 hours on average, 11% slept less than 6 hours at weekends and 41% had difficulty falling asleep.

One study looked at 26 Olympic athletes sleep and although they spent on average 8.5 hours in bed (30 minutes more than controls) they actually took longer to get to sleep (15 minutes difference) and woke up more in the night which resulted in similar sleep times to controls (7 hours) so having a poorer quality of sleep.

A questionnaire study of 632 German athletes showed two thirds slept worse than normal prior to competitions, 70% of these had problems going to sleep, half woke up early and a third woke up at night. Some of the reasons given by them were nervousness (60%), thoughts about competition (77%), unusual surroundings (29%) and noise (17%) .

A study of 283 elite Australian athletes 64% slept poorly prior to competitions, with falling asleep the main problem in 82%, and the main reasons given being thoughts about the competition (83.5%) or nervousness (44%). Of note is that 60% of team athletes and 33% of individual athletes had no strategy to overcome poor sleep.

In a collegiate basketball study athletes were not aware of how little they slept. They were also unaware that they were sleep deprived. The athletes in this study only had 6 hours 40 minutes sleep on average when measured objectively with actigraphy.

Another study assessed triathletes sleep who overtrained using actigraphy and showed that sleep duration and efficiency was reduced as well as an increase in upper respiratory tract infections.

Poor routines can significantly disrupt athletes’ sleep. Late bedtime and early morning training will lead to sleep restriction. Using laptops, smartphones, tv within an hour of sleep time will both increase brain arousal and suppress the secretion of the sleep synchronising hormone melatonin, resulting in delayed sleep onset and insufficient sleep resulting in daytime sleepiness. This is a particular problem in adolescent athletes who already have delayed sleep onset physiologically with sleep onset 12:44 am and wake time 8:18 am in one study and delayed further by 1-2 hours at weekends . Drinking too much fluid close to sleep onset will increase nocturnal waking to pass urine and caffeine should ideally not be consumed within 6-10 hours of sleep as it suppresses the sleep homeostatic drive. Alcohol is sedative initially but can depress breathing while asleep, increase snoring and results in early morning waking and poor sleep quality. Pain is another disruption to sleep. Late evening competition is also a sleep disruptor for many of the above reasons including travel and jet lag.

Lastly psychiatric or medical disorders or drugs including medications may disrupt sleep, and specific sleep disorders from which up to 1 in 3 people may be suffering.

Objective 2.2:To explain the effect of reduced quantity and and quality of sleep on athletes and athletic performance

Most of the studies done have looked at the effect of either complete sleep deprivation or partial sleep deprivation (sleep restriction)

Complete sleep deprivation

After 24 hours aerobic endurance running performance is reduced , confusion, vigor,fatigue and total mood disturbance scores were negatively affected but peak power was maintained . After 30 hours significant drop offs in mean and total sprint times occur and peak power starts to decrease after 36 hours . Sustained or repeated sub-maximal efforts seem to be more affected than one-off maximal efforts.

Also as wakefulness extends beyond 16 hours then reaction times and vigilance tests become similar to those of subjects with blood alcohol levels greater than 0.05% that is similar to the legal limit in Scotland for drink driving.

Partial sleep deprivation

Of greatest relevance to most athletes is sleep restriction. If sleep is for example restricted to less than 6 hours per night for four or more consecutive nights then immune function, regulation of appetite, glucose regulation, mood and cognitive performance are all impaired.

Psychomotor function and reaction times seem to be more affected than gross motor function (muscle strength, lung power and endurance running). Increases in depression, tension, confusion, fatigue and anger scores are all increased after only a few nights of partial sleep deprivation (2.5 hours). Sleep extension studies have supported this.

Again sub-maximal weight lifting efforts were affected to a greater degree than maximal efforts and occurred later in test protocols which suggest an effect of fatigue or mood/motivation due to only 2 nights of sleep loss .

Aim 3: To investigate how improving sleep in athletes affects their performance

Objective 3.1:To evaluate the effect of sleep extension on athletic performance

The majority of studies investigating the role of sleep in athletic performance have looked at the effects of sleep deprivation. Few studies have looked at sleep extension, especially in athletes. Earlier studies looking at young adults had only looked at short-term sleep extension to 10 hours in bed with mixed results.

The one that stands out is that done by Mah et al 2011. It is the first trial of the effects of sleep extension on athletic performance of actively competing athletes and is worth examining in a little detail. They took 11 elite college basketball players with an average age of 19.4 years during a competitive season and looked at their sleep and over a 2-4 week baseline period and then got them to extend their time in bed to a minimum of 10 hours for 5-7 weeks. They measured their sleep with diaries and actigraphy. To look at performance they looked at timed sprint, shooting accuracy. They also looked at reaction time, sleepiness and mood using various specific tests. Interestingly the athletes mean sleep times were 6 hours and 40 minutes at baseline on actigraphy (7 hours 50 on sleep diary) which indicates two things; first students don\’t get enough sleep and secondly that they are not great at measuring it.

After sleeping nearly 2 hours longer for several weeks, 10 hours 24 on sleep diary (8 hours 27 on actigraphy) the test results were impressive. Sprint times (16.2 seconds to 15.5 seconds), shooting accuracy ( free throw and 3-point field goal percentages both improved by 9%) , reaction times and sleepiness scores all improved and were statistically significant.

Also athletes measures of vigor, mood,fatigue,anger, depression, confusion and overall physical and mental wellbeing improved dramatically and were also statistically significant. This is an important finding as a common assumption that athletes become more fatigued as the season goes on, so sleep extension seems to reduce this effect, at least in this study.

The athletes did report that they felt they performed better in games, recovered quicker physically, had fewer injuries and could push more weights and do more conditioning but these were not formally measured. The other interesting finding is that they also felt in peak shape prior to sleep extension and admitted after the experiment that they had not appreciated how much actual sleep they needed to really peak their performance.

Mah’s group also conducted a similar sleep extension study on swimmers (10 hours a night for 6-7 weeks). They found that 15-metre sprint (0.51 sec), turn time (0.15 sec), reaction time (0.10 sec), kick strokes (5.0) and mood all improved.Mah also extended the sleep of collegiate American football players using the same regime and improved their 40 yard sprint times bu 2.1%.

Kolling (2016) also noted significant improvement in subjective recovery and stress scores in junior international rowers following a single night of extended sleep during a pre-world championship training camp.

Objective 3.2:To explore if any other interventions used to improve sleep actually affect athletes and their performance?

Naps taken after sleep loss have also been shown to be effective, improving reaction time, sprinting times and performance on vigilance tasks.

The timing and duration of the nap are also debated with a lunch to mid-afternoon 30 minute nap felt to be optimal, for late afternoon /evening performance. Waterhouse also showed that alertness and sleepiness was improved following the nap. Importantly this study was done after a night of sleep restriction. Naps were felt to be helpful for athletes who routinely have early morning training or who have sleep deprivation especially in preparation for evening competition.

Circadian variation of performance is also a factor, with maximal swim times varying through the day in college swimmers and work by Facer-Childs et al has shown that performance can improve by as much as 26% between early morning `and evenings in athletes who are late chronotypes, this may have an influence on team selection for evening games. Olympic athletes are however more likely to be early chronotypes according to Facer-Childs.

Adenosine levels in the brain build up with ongoing wakefulness and makes us feel sleepy. Caffeine inhibits adenosine effects and makes us feel less sleepy and as a performance enhancer.. Twenty minutes before a race I’ll normally drink some coffee to wake me up – if nothing happens – I have another shot. As I walk on to the stadium track I feel this massive caffeine high come on!” – Mo Farah

Getting a regular sleep/wake schedule, and practice relaxation techniques, tryptophan-containing foods prior to bedtime may help. Avoid bright light in the hour before bedtime.

If travelling then taking familiar bedding and avoiding sleep medication, alcohol and caffeine before bedtime. Also take time to get familiar with surroundings especially if flying across time zones.

Don’t nap too close to bedtime or for more than 30 minutes. Make a list of things to do, before bed to reduce worry. Try and get a regular sleep/wake time. Keep the bedroom cool, quiet and dark and get bright light on waking.

Remember there are no potions or pills that can replace good sleep. Avoid stimulants and big meals close to bedtime to sleep well.

Conclusions

I found the information for the first aim to be similar from most sources and not controversial with regard to the structure of sleep and showed how our sleep is deteriorating over the years. The functions of sleep are still being discovered. Rest, repair and memory consolidation were in most of the recent papers. The articles by Halson were really helpful. Accurate assessment of sleep is difficult without polysomnography as nothing else measures actual sleep.

I got a lot of original data for my second aim and showed that a lot of athletes just don’t get enough sleep but unfortunately no data to show how this affected their performances. The effects of complete sleep deprivation are agreed generally and not controversial but those of partial sleep deprivation are not so clear cut maybe because our measurements are not accurate both in and between studies. Fullagar’s work was helpful here.

For the last aim, I was really impressed by the work of Mah which showed that a lot of athletes are sleep deprived and don’t even know it. The effect of extending sleep in terms of reaction times, speed and accuracy was impressive. I was also surpised by how big a difference in performance could be found (26%) in late chronotypes .

Overall I think I met my aims and I think the answer to my question is that sleep definitely improves athletic performance but I am still not sure if that is just because we are all sleep deprived in the first place!

Evaluation of my performance

My review was on an emerging research area in sport. I could have designed my own study but couldn’t decide which was the best area or test to focus on, so instead I decided to produce an investigation based on secondary data. I chose only websites and reviews with links to peer reviewed journals based on original research. They were challenging to understand but I think I’ve given a good review of the current evidence. My bibliography list is long as I wanted to reference original work where possible.

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Appendix

Both copied from www.fatiguescience.com (accessed online 28th October 2016)

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