Sleep is the most powerful recovery and performance-enhancing tool on earth
Sleep is increasingly gaining attention among sport scientists and practitioners as an important element to optimise sports performance and recovery. In fact, due to its restorative aspect, sleep is a critical aspect of the recovery processes in athletes. Both physical and cognitive stress during athletes training sessions and competitions requires an appropriate recovery process to promote adaptation, avoid injuries and burn-out.
Moreover, sleep has a strong impact on health, from hormonal balance and immune system maintenance to metabolic control, every aspect of human physiology is under the influence of the quality and quantity of sleep. Additionally, Inadequate sleep has been consistently shown to negatively affects both physical and cognitive performance. Consequently, the optimization of sleep is an essential component of athlete preparation and sleep has been suggested to be the single most effective recovery strategy available to athletes1.
Sleep is a critical aspect of the recovery processes in athletes
On the other hand, the recommended amount of sleep to achieve optimal health and quality of life varies across the lifespan, with a gradual decrease from birth to older adulthood. Healthy adults require between 7 and 9hs. of sleep for optimal performance and health, while youngers require slightly more sleep, ideally between 8 and 10 h. Duration is only one component of sleep, however, the importance of sleep quality has been increasingly recognized as a vital element of overall health and well-being and it seems to improve as sleep latency, wake after sleep onset and nighttime awakening decreases 2.
What Sleep Is
The purpose of sleep is one of the biggest unsolved mysteries of biology3. Sleep is actually defined as a lab test outcome (electroencephalogram, electromyogram, electrooculogram and polysomnography) by recording the electrical field activity of large groups of cortical neuron and muscles3. Wakefulness is defined by low-voltage fast EEG activity (LVFA) and high muscle tone, NREM sleep is characterized by high-amplitude low-frequency EEG and decreased muscle tone, whereas REM sleep has LVFA coupled with a complete loss of muscle tone (REM muscle atonia) and characteristic rapid eye movements which contrast with the slow-rolling eye movements observed during NREM3.
Figure 1 Electroencephalographic (EEG) recordings capture differences between vigilance states (wakefulness, NREM sleep, and REM sleep)3.
The timing, depth, and duration of sleep are controlled by the interaction between sleep homeostasis and the circadian rhythm, taking into account that the latter affects the sleep timing, while homeostatic mechanisms regulate the need for sleep or sleep pressure4. The concept of coupled regulatory process with both homeostatic and circadian systems working together is called “RHEOSTASIS”, a term coined by Mrosovsky in 19905.
From an evolutionary standpoint, the circadian system is nothing but an anticipatory mechanism to environmental changes, such as temperature, radiation, and food availability, in a 24hs cycle4. In more complex organisms, like humans, this clock optimizes internal physiology to reduce energy expenditure and the use of internal recourses.
During the active phase, food intake and activity-related behaviours take place and during rest, maintaining and growth-related tasks arise. The evolution of a central nervous system did not change rest-activity cycles, but it added a further dimension as it seems the brain needs to go offline (sleep) during rest.
Figure 2 A representation of the two-process model of sleep regulation. The homeostatic process during a 48 hs period. Black and white bars represent the sleep-wake cycle, respectively. The Blue Line indicates an 8-16hs sleep-wake period; During the time period that the blue line increases the model is awake. When it reaches the upper threshold the model goes to sleep and the line decreases till reaching the lower threshold waking up again. The green line indicates the effects of a 2h nap around 18:00 followed by a normal night of sleep. The red line indicates sleep deprivation (40 h) and recovery sleep during the following night4.
As we already pointed out, there are 5 stages os sleep with different levels of consciousness and brain activity. These stages are known as 1, 2, 3, 4 and rapid eye movement (REM). Stages 1 to 4 within this cycle are typically referred to as nonREM (NREM) and are the progressions of sleep before the first episode of REM sleep occurs3. The cylce durations seem to be around 90 minutes and before the brain enters stage 1 the body seems to need between 5-20 minutes in a relaxed state with no stimulating activity ( e.g.; screen time). The total structure of sleep constitutes 75% NREM and 25% REM, with the majority of REM sleep met within the last third of nighttime sleep. A greater frequency and duration of REM is suggested to enhance recovery processes and lead to more optimal wakefulness6.
- Stage 1 non-REM sleep marks the transition from wakefulness to sleep. This stage typically lasts less than 10 minutes and is marked by a slowing of your heartbeat, breathing, and eye movements, as well as the relaxation of your muscles.
- Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep, lasts roughly 20 minutes. Stage two is characterized by further slowing of both the heartbeat and breathing and the brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles.
- Formerly known as stages 3 and 4, stage 3 (N3) is the final stage of non-REM sleep. This is the deepest period of sleep and lasts 20 to 40 minutes. Your heartbeat and breathing slow to their lowest levels, and your muscles are so relaxed that it may be hard to awaken you.
- REM sleep occurs 90 minutes after sleep onset and is a much deeper sleep than any of the three stages of non-REM sleep. REM sleep is defined by rapid eye movements and almost complete paralysis of the body, and a tendency to dream.
Figure 3 A typical sleep through sleep stages
There are several theories behind the function of sleep, however, the most accepted ones by the scientific community are (1) Sleep has a restorative effect on the immune and the endocrine systems, (2) sleep assists in the recovery of the nervous and metabolic cost imposed by the waking state, and (3) sleep has a vital role in learning, memory, and synaptic plasticity7,8.
There’s a link between inadequate sleep and increased risk of obesity, cardiovascular disease, stroke, diabetes and kidney disease
Behind those theories lies the foundation of why sleep quality, quantity and timing helps to improve memory and learning, increase attention and creativity, and aid in making decisions. Individuals that have not had adequate sleep may have difficulty making decisions, problem-solving, controlling emotions and coping with change. Lack of sleep is also associated with depression, suicide and risk-taking behaviour7,8.
Moreover, sleep is also essential for the maintenance of physical health, particularly in the healing and repair of cells. It also helps to maintain the balance of several hormones, such as ghrelin and leptin, which regulate feelings of hunger and fullness and is likely to explain the link between inadequate sleep and increased risk of obesity, cardiovascular disease, stroke, diabetes and kidney disease7,8.
In Addition, the processes of growth and development are also related to sleep. Deep sleep triggers the release of growth-promoting hormones, which boost muscle mass and repair cells and tissues in the body. The immune system also relies on sufficient quantity and quality of sleep and deficiency in sleep is linked to difficulty fighting infection and increased risk of getting ill7,8.
Finally, Sleep restriction (SR) occurs when humans fall asleep later or wake earlier than normal; that is, their normal sleep-wake cycle is partially disturbed. In contrast, sleep deprivation (SD) generally refers to extreme cases of sleep loss, whereby humans do not sleep at all for a prolonged period (i.e. whole nights)9.
Sleep, Performance and Recovery
More and more athletes are learning that sleep has a big impact on performance, wins, and losses. Physical conditioning and good nutrition are critical in reaching peak athletic performance, but sleep plays an equally important role. In recent years, it’s become clear that both the quality and quantity of sleep obtained by elite athletes can be the edge between winning and losing on game-day10,11.
Speed, endurance, strength, attention, executive function, learning and recovery can be affected by inadequate sleep.
Even though some early studies suggested that athletes possess similar or even superior sleep quality and quantity than nonathletic subjects12, it has also been shown that the sleep needs of athletes may be greater than healthy non-athletic individuals (9-10 vs 7-9) 13. However, recent evidence suggests that some athletes sleep far less than either of these recommendations14. Guidelines are far from perfect, and they don’t take into account the variability of sleep needs and characteristics across individuals, making sleep recommendations difficult, especially for athletes15.
There are multiple areas of performance that are substantially affected by inadequate sleep, including speed, endurance, strength, attention, executive function, learning and recovery. It has been shown that sleep loss, can negatively affect distance covered during time trials and sprint times16–18; reaction times, force production and strength19–22; increased perceived exertion23; reduce glycogen levels 18; reduce time to exhaustion24; increase metabolic stress markers such as heart rate, oxygen consumption and lactate levels25; Impairs recovery26. Moreover, mild sleep restriction can affect accuracy in athletic performance on an average of 53–37%27.
Moreover, maintaining and optimizing physical health is essential for peak athletic performance. The ability to stay healthy and avoid illness and injury is critical for athletes’ ability to perform. moreover being able to tolerate training loads are mandatory for elicit greater adaptation. There is accumulating evidence that insufficient sleep increases injury risk. Adolescents sleeping less than 8 h/night were found to be 1.7 times more likely to experience a significant injury than those who slept more than 8 h28. Also, the risk of developing a cold is greater with less than 6 h of sleep per night compared with sleeping 7 or more hours29. Athletes who showed consistency in sleep missed significantly fewer sessions due to fatigue and injury30. In addition, sleep restriction has been shown to negatively affect training load assimilation and subjective well-being31,32.
Furthermore, sleep is intimately involved in pain regulation, it has been reported an 8% decrease in pain threshold tolerance after a single night of total sleep deprivation33, and increases (5–10%) in spontaneously reported generalized pain after both total and partial sleep restriction34,35.
Interestingly enough, recent data has shown that sleep loss and circadian misalignments can, in fact, affect winning and losing. Evidence suggests that, in the same way, home-field advantage influences the probability of success, so too does the circadian advantage and its direction with an advantage for teams travelling eastward. There seems to be a circadian advantage in major sports leagues for teams travelling eastward and a circadian disadvantage for teams travelling westward because of the time zone changes, which impacts the alignment between the scheduled game times and the circadian peak performance36.
A recent study found that NBA teams travelling from west to east had a winning percentage of 45.38% compared with 36.23% for teams travelling from east to west. NHL teams travelling from west to east had a winning percentage of 47.62% compared with 42.48% for teams travelling in the opposite direction. NFL teams travelling from west to east had a winning percentage of 46.54% compared with 37.98% for teams travelling from east to west36.
Sleep Assessment and Practical Applications
Sleep assessment is not an easy task. In-lab polysomnography, the gold standard diagnostic test for primary sleep disorders, is too resource-dependent to be considered efficient and economical for use as screening tools. Even though technological advances led to an improvement in gadgets reliability, such as wrist actigraphs, there are still costly and time-consuming when large numbers of athletes are being assessed for sleep disturbance.
However, simple tools like questionnaires have been shown to be both valid and reliable and also simple, cheap and easy to implement. The Athlete Sleep Screening Questionnaire is a 15-items questionnaire structured around key sleep factors: ‘Total Sleep Time’ (night sleep, nap frequency and nap duration), ‘Insomnia‘ (time to fall asleep, trouble staying asleep, sleep medication usage), ‘Sleep Quality’ (satisfaction with sleep rated on a five-point scale), ‘Chronotype’ (preferred bedtime, preferred wake time, sleep inertia on awakening, morningness/eveningness rating), ‘Sleep Disordered Breathing’ (snoring, gasping while sleeping) and ‘Travel Disturbance’ (sleep disturbance while travelling, performance disturbance while travelling)37,38.
Optimal sleep can be achieved through simple lifestyle interventions.
- Evening electronic device use and lighting: Avoiding artificial light especially at night is essential to ensure restful sleep. Ideally, when the sun begins to fall, our exposure to artificial light should decrease39–44. If you have to stay awake the best hack I´m aware of is the use of special glasses designed to block blue light 45–51
Figure 4 Porfesional Boxer Using Blue Blocking Glasess.
- Strengthen your Circadian Rythm: Sunlight during the day protects against possible nighttime disruption from exposure to artificial light52. Sun exposure is the most important and effective tool to strengthen the circadian rhythm, with a few minutes (about 30 minutes) after getting up or even looking directly at the sun are enough, the trick is to do it at the same time always53.
- Develop a good sleep environment: The room where you sleep should be as dark as possible, without electronic devices of any kind, quiet and COLD, not so much that you are shivering, but a temperature of 18C or less is ideal. A good mattress and comfortable sheets are a plus.
- Avoid alerting factors in the evening: Avoid eating late at night, allow for a 30–60 min relaxing wind-down period before bed. Ideally, consume no caffeine after lunch; limit alcohol use in the late evening.