All About Sleep

Functions of Sleep

Sleep is essential: humans spend about one-third of their lives sleeping. Despite the common misconception that sleep is an idle state, one’s body does many things during sleep. Many things happen to your immune system, hormonal systems, thermoregulatory systems, and basic metabolic processes during this time (Simon).

Sleep plays an important role in physical recovery – particularly muscle recovery and repair – and adequate sleep (for teens, 8-10 hours is recommended) is crucial to avoid increasing risk of injury. If one does not get the amount and quality of sleep their body needs, they face increased stress, which “will impair recovery” (Comana 1).  Adequate sleep is crucial for optimal recovery and performance. Studies have shown that sleep extension is the most effective way to improve performance (Bonnar). Sleep extension is voluntarily increasing one’s sleep duration. This is especially important for student athletes, for improved performance and fast recovery.

Sleep deprivation in teenagers increases the risk of musculoskeletal (related to one’s muscles or skeleton) and other types of injuries. Teens who sleep less than 5 hours per night are nearly three times more likely to suffer from an occupational injury. An occupational injury would affect the athlete long term; including chronic pain, their mental health, and financial strain. These injuries can affect their daily lives, causing them intense pain and discomfort. The greatest amount of injury happens when one sleeps less than 5.5 hours. In a study originally done in 2014, it found that adolescent athletes who slept less than 8 hours per night were 1.7 times more likely to sustain a sport-related injury than their peers who slept at least 8 hours (R. Coel). Sleep deprivation affects one’s motor skills, performance, and mood.

Sleep is not only crucial for preventing injuries and supporting overall recovery, but it is especially important in the healing process after a concussion. However, concussions can disrupt normal sleep patterns, creating a bidirectional relationship between sleep and recovery. Individuals with mild traumatic brain injuries (mTBI) often report sleep disturbances such as insomnia, which includes difficulty falling asleep and poorer sleep quality (R. Coel). In a study with 158 individuals with a history of mTBI, 92%, people reported experiencing worse sleep quality following the injury (Towns SJ). Ensuring at least 8 hours of sleep before taking post-injury ImPACT (Immediate Post-Concussion Assessment and Cognitive Testing) can help minimize the risk of attributing symptoms to the concussion rather than sleep deprivation (R. Coel).

Lack of sleep or poor sleep can negatively impact cognitive performance (including memory, attention, and decision making), which is especially important for student athletes. Quality sleep is essential, which can be achieved by getting restful, uninterrupted sleep. Getting quality sleep has been shown to “improve reaction times by 15% and also improve objective daytime sleepiness,” while also having a “beneficial impact on the prefrontal cortex” that aids in proper decision making (Charest and Grandner). This can be crucial for an athlete during an important game. Even a small amount of sleep deprivation may impair their ability to make good decisions versus risky ones in a split second (Charest and Grandner).

In addition to its impact on cognitive performance, sleep also plays a critical role in regulating hormonal balance, another key factor in athletic performance. Changes to hormonal balance can cause an increased appetite, weight gain, insulin resistance, and more. These side effects can affect athletic performance by reducing energy, increasing fatigue, and sometimes affecting muscle function. One hormone especially important for athletes is the growth hormone. During every part of the day, growth hormone gets released in waves. During nighttime when one is sleeping more growth hormone is secreted. This is why scientists say that growth occurs the most during sleep (T. Kim). Growth hormone is important as an athlete because it can help with muscle growth and decreases fat mass.

Melatonin is one of the main hormones involved with sleep. Melatonin follows a strong daily rhythm, with levels being highest at the start of the night than during the day. It is controlled by the brain’s SCN (suprachiasmatic nucleus), which plays a crucial role in the body's internal clock. During the night the SCN sends signals to the pineal gland to secrete melatonin. Melatonin helps initiate sleep onset (the time it takes to go from wakefulness to sleep). It also helps to maintain a consistent sleep wake cycle (a natural 24 hour sleep schedule) (T. Kim). Melatonin is especially essential for athletes because it helps regulate your sleep-wake cycle. It helps with getting to bed at a proper time and staying asleep for a proper amount of time (T. Kim). For teenage athletes it is important to get 8-9 hours of sleep every night (R. Coel).

In addition to melatonin, other hormones also play a significant role in sleep regulation. One of these is cortisol, a hormone released by the body in response to stress, which also follows a circadian pattern. Specifically, cortisol rises during the night and peaks in the morning. There is also a correlation between cortisol levels and slow-wave sleep (SWS), or deep sleep. This is particularly important for student-athletes, as stress can affect sleep quality. During adolescence, natural shifts in circadian rhythms cause melatonin to be released later at night, making it more difficult to fall asleep early. This means it is esspecially crucial to prioritize relaxation (by establishing a routine, limiting screen time, and practicing relaxation like yoga or deep breathing) before bedtime to improve sleep (T. Kim).

Sleep deprivation is linked to increased appetite, which can contribute to insulin resistance and obesity. Disruptions in the circadian rhythm affect the hormones ghrelin and leptin. Ghrelin stimulates appetite, while leptin suppresses it. Sleep deprivation disrupts ghrelin levels, leading to random feelings of hunger and an increased desire to eat (T. Kim). It’s essential for athletes to get adequate sleep to help regulate appetite and ensure proper nutrition. For athletes, appetite regulation and proper nutrition are critical for their performance because it directly impacts energy balance, muscle recovery, and overall performance.

Additionally, insufficient sleep can negatively affect emotional well-being. Poor or limited sleep can lead to “intrusive, unwanted, off-task, and potentially ruminative thoughts” the following day (Charest and Grandner). Many student-athletes experience anxiety, with up to “37%” reporting anxiety compared to “7.1 to 26%” in adult athletes (Charest and Grandner). Caffeine is often used as a “countermeasure” to mitigate the effects of poor sleep on risk-taking and decision-making. It provides temporary energy and ultimately cannot replace the restorative processes the body undergoes during sleep (Charest and Grandner).

Beyond its emotional and cognitive effects, sleep deprivation also has a direct impact on the body’s physical recovery processes. For example it can significantly hinder recovery by “increasing proinflammatory cytokines,” which can exacerbate pain (Charest and Grandner). For context, proinflammatory cytokines are produced by immune cells and they signal molecules that promote inflammation. This impacts the immune system, “hindering muscle recovery and repair from damage” and contributing to “an imbalance of the autonomic nervous system” (Charest and Grandner).

Recommendations for Sleep 

Stimulus control techniques (e.g. establishing association between bed and sleep, go to bed when sleepy, avoiding daytime naps, and more) are helpful for creating a sleep environment that signals to the brain when and where it is time to sleep. This approach teaches the brain that the bed is exclusively for sleep: it should only be used for sleeping, not for other activities.

Other effective sleep recommendations include:

• Keeping the bed reserved for sleep, with no activities like eating or using electronics.

• Waking up at the same time every day, regardless of how well you slept the night before.

• Going to bed only when feeling tired, and not trying to “make up” for lost sleep by going to bed earlier than usual.

Creating an optimal sleep environment is crucial. Both the mind and body need to associate the bed with sleep, so that the message “This is where I sleep” is clear (Rantala). Consistency in sleep and wake times also helps reinforce this association. Napping, when used correctly, can be “very beneficial” for student athletes (Harper). Ideally, naps should last around 20 minutes. Longer naps that enter stages 3 or 4 of sleep may result in grogginess, making it harder to be alert for practice or competition (Harper). However, naps are not effective for overcoming the performance effects of jet lag, endurance racing, running economy, or complex gross motor skill acquisition (R. Coel). That said, naps have been shown to be one of the best interventions for improving physical and cognitive performance (Cunha). While caffeine may be used as a substitute for sleep, it should not be relied upon to compensate for inadequate rest. Caffeine can lead to increased anxiety at night, sleeplessness, and disrupts one’s natural sleep schedule. To ensure better sleep, caffeine intake should be cut off by 11 a.m. at the latest. Finally, it’s important to wind down before going to bed. About 30 minutes to an hour before bed; turning off electronics, dimming the lights, and engaging in quiet activities are all effective practices for promoting relaxation and preparing for sleep (Rantala). However, despite these strategies, some individuals may still struggle to maintain healthy sleep patterens due to underlying sleep disorders, which can further impact their physical and mental performance. 

Sleep Disorders

Insomnia is a sleep disorder that impairs one's abilities during the day, including “fatigue, emotional fluctuation, and psychomotor and/or neuropsychological performance,” which are all crucial for athletes (Charest and Grandner). Insomnia in athletes is not greatly understood. Many demands of athletes can lead to sleep difficulty or predispose them to insomnia, such as: “a high level of training volume, pre-competition anxiety, circadian challenges” and mentally, “a focus on success” (Charest and Grandner). 

Phase advance and phase delay are parts of a curve called Phase Response Curve (PRC), another sleep disorder. PRC is the reaction one’s circadian rhythm has to a stimulus (e.g. light exposure) ("Phase Response Curve (PRC)”). This shift causes phase advance or phase delay ("Phase Response Curve (PRC)”). Phase advance is when one has an earlier bedtime and wake up time, and phase delay is when one has a later bedtime and later wake up time.

Obstructive sleep apnea is a disorder where breathing stops and starts during sleep. This condition is more common in high-intensity sports, like “strength, power and high contact sports” (Charest and Grandner). These sleep disorders can be treated through lifestyle adjustments, medications, and some behavioral therapies. However, beyond medical treatment, the broader sleep culture surrounding athletes – how sleep is veiwed, prioritized and incorporated into training routines – also plays a significant role in maintaining optimal rest and performance.

Sleep Culture

In the United States “insufficient sleep is a sign of mental strength and a ‘badge of honor’” (Charest and Grandner). This mindset is inaccurate, adequate and healthy sleep is an absolute necessity. To prevent this disregard for sleep, athletes and their teams can create a healthy sleep culture. Some ways to create this culture are by “embracing the idea that sleep is essential to athletic performance and recovery” and lessening the guilt that comes with getting a full night’s sleep (Charest and Grandner). In addition, teams can screen athletes for sleep problems and incorporate these screenings into programs  (Charest and Grandner). This can also help diagnose and treat sleep disorders. By fostering a culture that prioritizes sleep as a fundamental aspect of performance and recovery, athletes can not only enhance their physical and mental well-being but also set a new standard for long- term health and success.

Resources

Bonnar, Daniel et al. "Sleep Interventions Designed to Improve Athletic 

Performance and Recovery: A Systematic Review of Current Approaches." 

Sports medicine (Auckland, N.Z.) vol. 48,3 (2018): 683-703. doi:10.1007/ 

S40279-017-0832-x

Charest J, Grandner MA. Sleep and Athletic Performance: Impacts on Physical Performance, 

Mental Performance, Injury Risk and Recovery, and Mental Health. Sleep Med Clin. 2020 Mar;15(1):41-57. doi: 10.1016/j.jsmc.2019.11.005. PMID: 32005349; PMCID: PMC9960533.

Coel, Rachel A et al. "Sleep and the Young Athlete." Sports health vol. 15,4 

     (2023): 537-546. doi:10.1177/19417381221108732

Comana, Fabio. "Exploring the Science of Recovery." American Fitness Magazine.   National 

Academy of Sports Medicine, blog.nasm.org/ the-science-of-recovery. Accessed 2 Dec. 2024.

Cunha, Lúcio A et al. "The Impact of Sleep Interventions on Athletic 

Performance: A Systematic Review." Sports medicine - open vol. 9,1 58. 18 

Jul. 2023, doi:10.1186/s40798-023-00599-z

Harper, Shelley. "The Physiology of Naps and the Impact on Athletic 

     Performance." Bridge Blog, 14 July 2017, blog.bridgeathletic.com/ 

     the-physiology-of-naps-and-their-benefits-for-athletes#:~:text=Naps%20can%20be%20 

     very%20beneficial,could%20impede%20their%20athletic%20performance. Accessed 

     8 Dec. 2024.

Kim, Tae Won et al. "The impact of sleep and circadian disturbance on hormones 

     and metabolism." International journal of endocrinology vol. 2015 (2015): 

     591729. doi:10.1155/2015/591729

"Phase Response Curve (PRC)." Circadian Sleep Disorders Network, 

     www.circadiansleepdisorders.org/info/PRC.php. Accessed 7 Dec. 2024.

Rantala, Amy, M.D. "Sleep Your Way to Better Athletic Performance." Speaking of 

     Health. Mayo Clinic Health System, 18 Dec. 2023, 

     www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/ 

     sleep-and-athletic-performance. Accessed 7 Dec. 2024.

Simon, Katharine C et al. "The functions of sleep: A cognitive neuroscience 

     perspective." Proceedings of the National Academy of Sciences of the United 

     States of America vol. 119,44 (2022): e2201795119. doi:10.1073/ 

     Pnas.2201795119

Towns SJ, Silva MA, Belanger HG. Subjective sleep quality and postconcussion 

     symptoms following mild traumatic brain injury. Brain Inj. 

     2015;29(11):1337-41. doi: 10.3109/02699052.2015.1045030. Epub 2015 Aug 7. 

     PMID: 26288022.

Kirschen, Gregory W et al. “The Impact of Sleep Duration on Performance Among Competitive Athletes: A Systematic Literature Review.” Clinical journal of sport medicine : official journal of the Canadian Academy of Sport Medicine vol. 30,5 (2020): 503-512. doi:10.1097/JSM.0000000000000622

Cunha, Lúcio A et al. “The Impact of Sleep Interventions on Athletic Performance: A Systematic Review.” Sports medicine - open vol. 9,1 58. 18 Jul. 2023, doi:10.1186/s40798-023-00599-z