Sportspeople go to great lengths to improve their performance, spending considerable time and effort on a number of technical, physical, and psychological strategies. However, strategies aimed at improving something as basic as sleep are often overlooked.
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When I was the general manager of a large junior golf programme, it always purplexed me watching students work very hard throughout the day (with some practising up to 6 hours), to then return to their accommodation and stay up until around 1am (waking up approximately at 7.30am). This would happen regularly, whether the following was a practice or competition day. All that effort and endeavour to improve but they ignored the need to get a good nights sleep. I assume, because they didn't believe it would have much effect on their performance?
However, research into the link between sleep and performance has shown sleep can influence a number of performance factors, such as an athlete's reaction-time, accuracy, memory, fatigue, and likelihood of illness or injury.
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Accuracy
The difference between winning and losing in sport can be minuscule, and even the slightest err in accuracy can have a major impact on the outcome of an event. Accuracy is an integral part of success in many sports. For example, the ability to hit a double 20 in darts, hit a passing shot down the line in tennis, or to kick a field goal in rugby all require precision.
Research has illustrated just how important sleep is in regards to performance accuracy. For example, Edwards and Waterhouse (2009) completed a study investigating the effect of restricted sleep on the accuracy and consistency of dart throwing. The researchers looked at the difference in the dart throwing performance of sixty participants after a normal nights sleep (7-8 hours), compared to after a night of restricted sleep (3-4 hours sleep).
The participants were asked to throw 20 darts at a target, where they received a higher score for a dart that landed closer to the centre of the target. A score of 10 points was given for hitting the centre, reducing to 1 point for the outer ring (see image), and a score of 0 for missing the board completely.
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The results showed that after a night of restricted sleep, the participants returned an average score of 3.61 compared to 4.16 after a normal nights rest (a 14% drop in performance). They were also 1.3 times more likely to miss the target completely, and were more inconsistent with their throwing.
Another sleep reduction study by Reyner and Horne (2013) which looked at the serving ability of 16 semi-professional tennis players, found that a reduction in sleep reduced accuracy in a serving task by over 40%. The task was to serve 40 balls and hit at a pre-defined target (see image below). Participants were tested after normal sleep (6.5 to 8 hours), and also after restricted sleep (5 hours).
A similar study by Schwartz and Simon (2015) looked at the effect of sleep extension on tennis serving accuracy. The researchers measured the participant’s sleep habits for a week to gain a baseline measure, and established they slept on average 7.14 hours per night. For the following week, the participants were instructed to try and increase their sleep to 9 hours sleep per night. Results showed they did manage to extend their sleep to 8.85 hours per night, and the increase in sleep (1.71 hours) improved serving accuracy from 35.7% to 41.8%.
Sleep extension was also shown to improve free-throw and 3 point shooting accuracy of a Stanford University basketball team. Mah, Mah, Kezirian, and Dement (2011) firstly established baseline sleep patterns over a 2-4 week period. This was followed by a 5-7 week period where the participants were instructed to sleep as much as possible at night, with the aim of achieving at least 10 hours per night. Sleep increased from 7.8 (baseline) to 10.4 (sleep extension) hours per night. Increased sleep led to an increase in free-throw success and 3 point shooting during a practice session by 9% and 9.2% respectively.
Sleep deprivation appears to decrease accuracy, while sleep extension increases it. This finding is especially important for athletes in sports where success is heavily influenced by accuracy, e.g. sports such as darts, tennis, golf, bowling, basketball, badminton, etc. Athletes are well aware of the impact a reduction in accuracy can have on performance, and therefore should be highly motivated to improve their sleeping habits in light of these results.
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Illness
Sir Dave Brailsford, the performance director of the successful British Cycling team between 2003-2014, understood the importance of staying healthy. In the attempt to avoid illness, he once hired a surgeon to teach athletes how best to wash their hands (germs can be spread from person to person contact but hand washing removes the germs that can make you sick). He also instructed his athletes to avoid shaking hands with others while at competitions (e.g. Olympics) to reduce the chance of catching any last minute illnesses.
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Avoiding illness is important for an athlete as being ill will prevent them from being able to successfully train or compete. Implementing strategies that reduce the chances of the onset of illness is of great benefit to an athlete.
There is a growing body of scientific evidence that shows acquiring sufficient sleep helps reduce the onset of illness. During sleep, proteins such as cytokines, and antibodies are released to help fight infection, e.g. bacteria and viruses. However, when lacking sleep, the production of such proteins may be reduced, preventing your immune system from functioning at its best, making it more likely that you will get ill.
Cohen, Doyle, Alper, Janicki-Deverts, and Turner (2009) conducted a study where the participants were exposed to a rhinovirus (the virus that is the predominant cause of a common cold) via a nasal drop. The researchers wanted to learn whether differences in sleeping duration and quality would influence whether exposure to the rhinovirus lead to illness or not. I.e. does sleep provide any immunity against the common cold? The sleep patterns of 153 participants were monitored over a 2 week period. Then, they were subjected to the rhinovirus and monitored for a further 5 days to assess any signs of illness. The researchers learned that participants who had averaged less than 7 hours of sleep per night, were nearly 3 times more likely to develop a cold compared to those who had averaged 8 hours or more.
The quality of sleep also influenced whether a participant would develop a cold. Participants who had less than 92% sleep efficiency (which is the percentage of time a person is asleep - from the time they lie down to sleep until the time they wake up the following morning), were 5.5 times more likely to develop a cold compared to those who had achieved at least 98% sleep efficiency or more.
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Sport participation presents a number of obstacles to attaining sufficient sleep. One of these obstacles is the experience of fatigue from the volume of training that is required.
Too much training can lead to overtraining. Overtraining is characterised by an increase in intensity, duration, and/or frequency of training, which prevents an athlete from adequate recovery.
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Hausswirth, Louis, Aubry, and Bonnet (2014) studied athletes over a 6-week period, and found that an increase in training volume had a negative effect on a person’s sleep quality, and made it more likely that an athlete would succumb to an infection, such as a common cold.
The study included 27 participants, who were placed in a ‘normal’ training group or an ‘overloaded’ training group. Training sessions in the overloaded group were 30% longer in duration in comparison to the normal group.
At the completion of the study, participants were assigned to one of three groups. The overtrained group which showed declines in performance (suggesting this group was most effected by fatigue), the overtrained group which showed no decline in performance, and the normal training group. The prevalence of higher upper respiratory tract infections (e.g. cold) for each group was 67%, 22%, and 11% respectively, which support the theory fatigue and lack of sleep increased the likelihood of getting ill.
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Injury
As with illness, avoiding injury is vitally important for an athlete. Injuries can strike at any time, which can prevent an athlete from being able to train or compete.
You have learnt that an increase in training alongside a reduction in sleep increases the likelihood of becoming ill, and it can also increase the risk of injury. Von Rosen, Frohm, Kottorp, Friden, and Heijne (2017) monitored the sleep, training, and injuries of 496 adolescent athletes from 16 different sports, weekly, for a period of one year.
43% of athletes reported getting an injury during the study. The researchers looked at the sleep and training habits the week prior to the injury, and compared these to earlier weeks. The researchers found that an increase in training duration and intensity, coupled with a reduction in sleep, made it more than twice as likely that an athlete would get injured.
Another relatively large study by Milweski et al. (2014) surveyed 112 high school athletes on the number of hours sleep, on average, they acquired each night. The researchers then looked at the school’s injury records, looking back over the previous 21 month period. They discovered that athletes who slept for less than 8 hours per night, on average, were 1.7 times more likely to have had an injury compared to those who had slept for more than 8 hours per night.
MODULE SLEEP
Evidence
Reaction Time
Success in many sports depend on an athlete’s ability to react and make split second decisions. For example, how a sprinter reacts to the start gun could make the difference between winning or losing a race. A cricket batsman needs to react quickly to a ball that can be bowled over 150kph. A goalkeeper has to make a quick decision on whether to come out of his area to catch a cross, or stay on his goal line. There are endless examples of situations that illustrate the importance of an athlete's ability to react.
​Do you think being intoxicated has a negative effect on your ability to react quickly? Would you compete while intoxicated? Hopefully the answer to those questions was yes and no, respectively.
It is widely accepted that alcohol consumption impairs our concentration, reaction, coordination, and decision making process, and if you are of drinking age, it is quite likely that you may some personal experience in these matters. A study by Williamson and Feyer (2000) showed that a lack of sleep produces a similar decline in reaction time to that of being intoxicated. The study involved 30 participants (aged 30-49), who completed tasks (e.g., reaction time and hand eye coordination tests) when sleep deprived, and again while intoxicated to compare any differences.
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For the alcohol test condition, participants woke up at 6am, and were given doses of alcohol at 4 hourly intervals starting from 8am, with the intention of increasing their blood alcohol concentration (BAC) level to .025%, .05%, .075%, and .1% after each dose. The participants completed a series of test at the start, and then 30 minutes after consuming each dose of alcohol. For the sleep deprived condition, participants woke up at 6am, and completed 15 series of tests at varying times over the next 28 hours, without any sleep during that time.
BAC is an indicator of one’s intoxication, and refers to the percent of blood that is concentrated with alcohol. E.g. a BAC of 0.05% means you have 0.05g of alcohol in every 100ml blood. The legal driving limit for BAC in the UK is 0.08% (except Scotland which is 0.05%).
The researchers discovered performance decrements in both conditions. After 17-19 hours without sleep the performance on most tests were similar to when participants had a BAC of 0.05% (illegal driving limit in Scotland).
Taheri and Arabameri (2012) also found sleep deprivation had a negative influence on reaction times. Participants completed a reaction test which involved a computer that was connected to two joysticks (one for each hand). Two empty squares were shown horizontally on a computer monitor. When one of the squares filled with red, the participant had to tilt the appropriate joystick as quick as possible (to signify whether it was the left or right square that was filled red). Participants were tested after at least three nights of regular sleep, and then when sleep deprived (kept up overnight and completed the test at 9am in the morning). When sleep deprived, their reaction time slowed by 15%.
However, it is likely there will be few occasions where you will need to compete after being awake for 17-19 hours. So how do more realistic levels of sleep loss affect reaction time?
Suppiah, Low, and Chia (2013) looked at the sleeping patterns of 29 male high school athletes. They discovered that during weekdays, the students incurred a sleep debt, i.e., they slept on average for just 5.5 hours per night. However, over the weekend, students extended their hours of sleep, most possibly due to the fact they did not have to get up early to attend class. On reaction time tests, the athletes performed faster on Monday compared to Thursday and Friday. The hypothesis was, athletes performed worse at the end of the week because of the sleep debt they had incurred during the week, compared to monday when they were better rested after the weekend.
A similar study was conducted by Vedaa, Saxvig, Wilhelmsen-Langeland, Bjorvatn, and Pallesen (2012) with Norwegian junior school students. The students started their day at 9.30am on Monday (1 hour later than normal). Their start time was 8.30am for the remainder of the school week. The researchers wanted to learn whether the opportunity of extra sleep on the Monday would affect performance in a reaction time test. Sleep duration was measured and the students achieved at least 1 hour more sleep on Sunday night in comparison to control group (which was a group of different junior high school students who started at 8.30am, Monday to Friday). The results of the reaction test showed that the students from the school who received the additional sleep on Sunday night, performed better on Monday compared to Friday, relative to the control group.
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Van Dongen, Maislin, Mullington, and Dinges (2003) showed that cumulative sleep loss (sleep debt across multiple days) also has a negative effect on a reaction time task. Participants were randomly assigned to one of the following groups where their sleep was restricted to either:
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4 hours per night for 14 days
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6 hours per night for 14 days
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8 hours per night for 14 days
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3 nights without any sleep
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The results showed reaction time erroded for the 4 and 6 hour group (worst for the 4 hour group) relative to the 8 hour group, and performance fell to a level that was equivalent to those that were totally sleep deprived for 1 to 2 days! So sustained sleep restriction even over a relatively short period of time seems to impair reaction times.
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Mood
Getting into the right state of mind is critical for performance. In general, mood can be described as positive and negative, and the research into the relationship between mood and performance suggests that a positive mood is better.
Excitement, joy, and happiness have been associated with better concentration, confidence, motivation, and capability, compared to negative moods such as anger and frustration. When we are happy and enjoy what we are doing, it is easier for us to focus on the task at hand as we become engrossed in the activity. In contrast, when we are unhappy we can be easily distracted and disengaged with the activity.
Enjoyment is a big reason why athletes participate in sport. The more we enjoy something the more likely we are to repeat it. If we associate negative mood with an activity, it is possible that over time we will want to avoid it, e.g. dropout of the sport altogether.
A study by Lastella, Lovell, and Sargent (2014) looked at whether sleep before the night of a marathon event influenced the pre-competitive mood of 103 runners (participants). On the morning of the event, the participants completed a survey about their previous nights sleep and their current mood. The results showed that a reduction in sleep quality and/or sleep duration had a negative influence on the mood of the athletes, e.g., the athletes felt more tension and fatigue.
Dingles et al. (1997) restricted the sleep of 16 participants to just 5 hours per night, for a week long period. The cumulative sleep debt produced elevation in participants ratings of fatigue, confusion, tension, and stress. Interestingly, it took 2 nights of normal sleep (approximately 8 hours) before mood returned to a normal level.
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Learning and Memory
Whether it’s developing skills, psychological techniques, or improving tactical knowledge, an athlete will rely on their memory to facilitate learning. The entire learning process depends on one’s ability to process, store, and retrieve information from memory. Sleep is believed to play a critical role in the consolidation of memory.
Research conducted by Talamini, Niewwenhuis, Takashima, and Jensen (2008) found memory recall was enhanced with sleep, and the sooner sleep was obtained after learning, the better. Participants completed a face-location memory task. They were shown an image of a face, and then one of 8 dots were highlighted (see picture). There were 20 different images in total that the participant had to remember, as well as the dot location, which varied.
The participants were split into two groups. One group completed the learning and initial test session in the morning (10am), and had no sleep before a recall test 12 hours later (10pm). The other group completed the learning and initial test session in the evening (10pm), and slept before the recall test, which was also 12 hours later (10am). Success was measured by how many correct answers were recalled in the second recall test compared to the initial test. The results (shown below), show that the memory recall was better for the group who had slept between the learning session and recall test.
Group
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1
2
Initial
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10am
10pm
Condition
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No Sleep
Sleep
Recall
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10pm
10am
Diff.
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-7%
+1%
It is possible that the 'Sleep Group' produced better recall than the 'No Sleep Group' because of a reduction in intereference. I.e., the 'No Sleep Group' had to deal with further information and activities throughout the day which may have interfered with their ability to recall the learned information.
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However, the researchers tested two additional groups over 24 hours (results below) and both had the same amount of awake time. So it appears sleep may have a beneficial influence on memory, and memory may be better when sleep directly follows learning, as both groups that slept straight after learning performed best on the recall test.
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A study conducted by Yang Et al. (2014) showed that sleep (in mice) soon after learning a skill produced a change in synaptic plasticity (which is believed to enhance learning and memory) compared to mice who were kept awake for 8 hours. When they were tested 5 days later, the mice who had a sleep delay had still not caught up (even with additional learning sessions!).
But what about the effects of naps on memory? A study by Lahl, Wispel, Willigens, and Pietrowsky (2008) found naps improved declarative memory (memory of facts) recall. Participants were tasked with memorising a list of 30 words. After an initial learning session, there was a 60 minute break before a recall test. Participants spent this break either:
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Awake - spent the 60 minute break playing simple computer games.
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Long nap - put to bed and woken after a 50 minute period, 10 minutes before the recall test. The researchers measured the actual time the participants slept (e.g. it may have taken some time for a participant to fall asleep), and the average sleep recorded was 36 minutes for this group.
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Short nap - put to bed and after approximately 5 minutes of recorded sleep were awoken. The actual average sleep recorded for this group was 6 minutes.
The results showed that recall after a long nap was significantly better compared to the recall of participants who stayed awake during the 60 minute break. Interestingly, even recall after a short nap of around 6 minutes was enough to signficantly enhance performance in comparison to the awake group.
So ensuring you get sufficient sleep is important before and after games/training. If you can improve your sleep it's likely you will improve your learning, and perhaps taking naps or sleeping soon after a training session may provide additional benefit.
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Fatigue
The association between fatigue and a lack of sleep seems a bit of a no-brainer. Who hasn't experienced the feeling of fatigue from a lack of sleep at some stage in their life?
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Sargent et al. (2014) completed a study that showed sleep deprivation effects an athlete's fatigue. 70 elite athletes across 7 sports, recorded their sleep, training, and perceived fatigue levels prior to each training session over a period of 2 weeks. It was discovered, as you would expect, less sleep was associated with higher levels of fatigue.
Fatigue can have a detrimental effect on your performance, due to a lack of energy, concentration, etc.
It can also effect your training, as you are likely to reduce your intensity, training time, and enjoyment, which is likely to have a negative knock-on effect on future behaviour and outcomes.
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However, it has been suggested that the impact of a lack of sleep on performance will vary across different sport activities. E.g., a study by Taheri and Arabameri (2012) showed that sleep debt had no effect on a short anaerobic exercise. Participants cycled (in a laboratory setting) as fast as they could for a period of 30 seconds, and their performance was unaffected after a night of no sleep. In the same study, participants also completed a reaction time test and the lack of sleep did have a negative effect on reaction time. These finding supports the belief that sports that are short in duration, and rely on anaerobic exercise or power are less likely to be affected by sleep loss. Whereas, fine motor skill sports, such as shooting, golf, darts, that rely more on cognitive functions will be more readily affected by sleep deprivation.
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Overview
The research into the impact of sleep suggests it has a significant impact on performance across a range of sporting activities. Attaining sufficient sleep duration and sleep quality appear to improve reaction time, accuracy, mood, and reduce susceptibility to illness and injury. However, any effects on anaerobic power, strength, and sprint performance remain less clear.
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As an athlete you dedicate so much time and effort into your training and performance, but if you do not take care of something as basic as your sleeping habits, you are harming your chances of reaching your full potential. When designing practise schedules, athletes and coaches need to consider the timing of training sessions and how it may affect sleep. Where early morning starts are unavoidable, strategies to help sleep in the evening and/or daytime naps would be beneficial.
It seems clear there is a link between performance and sleep, so be smart and implement sleep management strategies to your training programme. To help track and improve sleeping patterns, athletes can take advantage of modern technology currently available or through manual recording.
Group
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1
2
Initial
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10am
10pm
Order
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Wake - Sleep
Sleep - Wake
Recall
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10am
10pm
Diff.
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-12%
-3%
References
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Dingles, D.F., Pack, F., Williams, K., Gillen, K.A., Powell, J.W., Ott, G.E., Aptowicz, C., & Pack, A.L. (1997). Cumulative sleepiness, mood disturbance, and psychomotor vigilance performance decrements during a week of sleep restricted to 4-5 hours per night. Sleep, 20 (4), 267-277.
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Edwards, B.J, & Waterhouse, J. (2009). Effects of one night of partial sleep deprivation upon diurnal rhythms of accuracy and consistency in throwing darts. Chronobiology International, 26 (4), 756-768.
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Hausswirth, C., Louis, J., Aubry, A., & Bonnet, G. (2014). Evidence of disturbed sleep and increased illness in overreached endurance athletes. Medicine and Science in Sports and Exercise, 46 (5), 1036-45.
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Lahl, O., Wispel, C., Willigens, B., & Pietrowsky, R. (2008). An ultra short episode of sleep is sufficient to promote declarative memory performance. Journal of Sleep Research, 17 (1), 3-10.
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Lastella, M., Lovell, G.P., & Sargent, C. (2014). Athlete's precompetitive sleep behaviour and its relationship with subsequent precompetitive mood and performance. European Journal of Sport Science, 14 (1), 123-130.
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Mah, C.D., Mah, K.E., Kezirian, E.J, & Dement, W.C. (2011). The effects of sleep extension on the athletic performance of collegiate basketball players. Sleep (34), 7, 943-950.
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Milewski, M.D., Skaggs, D.L., Bishop, G.A., Pace, J.L., Ibrahim, D.A., Wren, T.A., & Barzdukas, A. (2014). Chronic lack of sleep is associaed with increased sports injuries in adolescent athletes. Journal of Pediatric Orthopaedics, 34, 129-133.
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Reyner, L.A., & Horne, J.A. (2013). Sleep restriction and serving accuracy in performance tennis players, and effects of caffeine. Psychology and Behaviour, 120 (4), 93-96.
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Sargent, C., Lastella, M., Halson, S.L., & Roach, G.D. (2014). The impact of training schedules on the sleep and fatigue of athletes.
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Schwartz, J., & Simon, R.D. (2015). Sleep extension improves serving accuracy: A study with college varsity tennis players. Physiology & Behaviour, 151, 541-544. Chronobiology International, 31 (10), 1160-1168.
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Suppiah, H.T., Low, C.Y., & Chia, M. (2016). Effects of sport-specific training intensity on sleep patterns and psychomotor performance in adolescent athletes. Pediatric Exercise Science, 28 (4), 588-595.
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Taheri, M., & Arabameri, E. (2012). The effect of sleep deprivation on choice reaction time and anaerobic power of college student athletes. Asian journal of sports medicine, 3 (1), 15–20.
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Talamini, L.M., Nieuwenhuis, I.L., Takashima, A., & Jensen, O. (2008). Sleep directly following learning benefits consolidation of spatial associative memory. Learning and Memory. 15 (4), 233-237.
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Vedaa, O., Saxvig, I.W., Wilhelmsen-Langeland, A., Bjorvatn, B., & Pallesen, S. (2012). School start time, sleepiness and functioning in Norwegian adolescents. Scandinavian Jounral of Educational Research, 56 (1), 55-67.
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Van Dongen, Hans P.A., Maislin, G., Mullington, & J. M., Dinges, D.F. (2003). The Cumulative Cost of Additional Wakefulness: Dose-Response Effects on Neurobehavioral Functions and Sleep Physiology from Chronic Sleep Restriction and Total Sleep Deprivation. Sleep, 26 (2), 117–126. Web.
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Von Rosen, P., Frohm, A., Kottorp, A., Friden, C., & Heijne, A. (2017). Multiple factors explain injury risk in adolescent elite athletes: applying a biopsychosocial perspective. Scandinavian Journal of Medicine and Science in Sports, 27 (12), 2059-2069.
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Williamson, A.M., & Feyer, A.M. (2000). Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication. Occupational and Environmental Medicine, 57 (10), 649-655.
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Yang, G., Lai, C.S., Cichron, J., Ma, L., Li, W., & Gan, W.B. (2014). Sleep promotes branch-specific formation of dendritic spines after learning. Science, 344 (6188), 1173-1178.