“People say, ‘I’m going to sleep now,’ as if it were nothing,” said comedian George Carlin. “But it’s really a bizarre activity. For the next several hours, while the sun is gone, I’m going to become unconscious, temporarily losing command over everything I know and understand. When the sun returns, I will resume my life.”
Indeed, sleep is somewhat bizarre. During this “natural periodic suspension of consciousness during which the powers of the body are restored,” we experience several stages and cycles of sleep and we temporarily lose control of our skeletal muscles. We enter alternate realms through our dreams, and our bodies release human growth hormone (HGH)–which can improve fitness and sports performance.
Sleep is our best friend or our worst enemy. When it comes to exercise performance, we also want sleep to be our most important training partner. It can be argued that it’s not training that improves performance; it’s the sleep we get each night that improves our outcomes. “Sleep duration may be an important consideration for an athlete’s daily training regimen,” says Cheri Mah, PhD, of the Stanford University Sleep Disorders Clinic and Research Laboratory (AASM 2010). This article looks at why we need sleep and reviews research that supports it as a primary means of reaching health and fitness goals.
Why Do We Sleep?
There are three theories for why we need sleep (Frank 2006). The restorative theory states that sleep restores the deficits of living that accrue when we are awake. The body repairs nerve cells and tissues, and the brain integrates new information and organizes memory. The adaptive theory suggests that sleep may have evolved as an adaptive and protective function: Our ancestors searched for food during the day, and at night, sleep kept them safely hidden away from predators. The third theory, the information consolidation theory, is based on cognitive research and suggests we sleep in order to process information acquired during the day. This theory also argues that sleep allows the brain to prepare for the day ahead and helps put learned information into long-term memory.
Overview of Healthy Sleep
During the night, human beings cycle through five stages of sleep in a pattern called sleep architecture. There are seven cycles of sleep, each lasting 1-1.5 hours; in every complete cycle, the body moves through all five sleep stages. The stages include non-rapid eye movement (NREM) sleep (stages 1-4) and rapid eye movement (REM) sleep (stage 5). Typically, we move from the waking state into a period of non-REM sleep, which is followed by a short period of REM sleep. The cycle then begins again. As the night progresses, the periods of REM sleep get longer (National Sleep Foundation 2013).
Stage 1 is light sleep, where the body begins to lose muscle tone, muscles twitch and there’s a loss of self-awareness. This transition phase, in which we drift into sleep, lasts approximately 5-10 minutes (National Sleep Foundation 2013). It is an important phase because it allows the body to slow down and muscles to relax. Nearly all muscle tone is lost in stage 2, a light dreamless sleep. We spend half our sleep in this stage. Brain activity, heart rate and breathing slow down. Body temperature falls (a cooler temperature in the bedroom helps sleep), and the body reaches a state of total relaxation in preparation for deeper stages of sleep.
Stage 3 marks the beginning of deep sleep, also known as slow-wave sleep. This is when HGH starts to be released. Stage 4, the deepest slow-wave sleep, helps to replenish physical and mental energy. During this stage, the body does most of its repair and regeneration work, thanks primarily to a continual release of HGH.
Because this hormone is being released in stages 3 and 4, some fitness and sports performance trainers call sleep “the athlete’s steroid.” HGH helps maintain and repair muscles and cells, and it is key to improving athletic performance (McArdle, Katch & Katch 2009). As a result, you might argue that sleep is one key to fitness and sports performance. In reality, however, the key may lie in finding the correct balance of training, rest, nutrition and sleep.
During stage 5, REM sleep, the eyes dart back and forth. People who experience healthy sleep spend 25% of the night in this stage (National Sleep Foundation 2013). It is when dreaming occurs, which is important for healthy brain function. Dreaming also provides energy to brain and body and helps create long-term memories. The arms and legs experience periods of paralysis, which is thought to protect us from acting out our dreams. REM sleep also stimulates brain regions used in learning. This may be important for normal brain development during infancy, which could explain why infants spend much more time in REM sleep than adults.
The Sleep Abyss
How much sleep we need varies from person to person. Generally speaking, most adults need 7-9 hours of uninterrupted sleep per night (National Sleep Foundation 2013).
Short sleep and poor-quality sleep appear to be endemic in modern society (Van Cauter et al. 2008). Most adults get about 6.5 hours of sleep per night. Many people think that decreasing their sleep to minimum tolerability is harmless and also efficient because they can get more done. However, sleep loss accumulates into sleep debt. Over a 5-day workweek, a nightly sleep loss of 90 minutes builds into a 7.5-hour sleep debt by the weekend. This equates to losing one full night of sleep during the workweek. Losing 2 hours of sleep a night (sleeping 6 hours instead of 8) significantly impairs performance, attention, working memory, long-term memory and decision making (Alhola & Polo-Kantola 2007).
Poor sleep, or lack of sleep, impairs cognitive function and makes it difficult to perform the simplest of tasks. It can also make it very hard to remember things. There’s a link between sleep deprivation and many psychological disorders, including depression (Taylor et al. 2005; Colten & Altevogt 2006). Here are some of the most common symptoms of chronic poor sleep:
- memory loss
- high blood pressure
- overall fatigue
- muscle aches
Partial sleep deprivation has also been found to influence attention, especially vigilance (Alhola & Polo-Kantola 2007). In people who got 6 hours of sleep when they normally got 8, the effect on performance was similar to drinking two or three beers. This equated to approximately 0.05% breath alcohol levels. Losing 4 hours of sleep equated to a 0.1% breath alcohol measurement (Rosekind 2008). How does this relate to personal training clients? It’s difficult to improve fitness when the symptoms of poor sleep are present. How can clients get a great workout when they have a headache and they’re tired and irritable?
If one of your clients is sleeping poorly or is not sleeping long enough, it’s important to address the issue. Since HGH helps build and repair muscle mass, tissue and cells, imagine how simply getting 60-120 minutes more of quality sleep could improve performance.
Sleep and Sports Performance
Research has shown that the healing powers of slumber can assist exercisers in reaching their performance goals. Even a nap has been found to improve performance, alertness and accuracy on a reaction time test (Waterhouse et al. 2007). Ten men napped or sat quietly for 30 minutes after a night of only 4 hours of sleep. Thirty minutes after the nap, study designers recorded alertness, short-term memory, heart rate, reaction time, grip strength, and times for 2-meter and 20-meter sprints. The researchers found that the nap lowered heart rate. Alertness, sleepiness, short-term memory, accuracy and reaction time also improved in the nappers. Sprint times decreased by 0.041 seconds for the 2-meter sprint and by 0.093 seconds for the 20-meter sprint.
In 2008, Mah, Mah and Dement studied college swimmers who, for the first 2 weeks of the study, maintained their usual sleep-wake patterns and were tested on 15-meter swim sprint time, reaction time off start blocks, turn time and number of kick strokes. The athletes then extended their sleep to 10 hours per day for 6-7 weeks. They were tested again, and results showed that the swimmers swam the 15-meter sprint 0.51 seconds faster, reacted 0.15 seconds sooner off the start blocks, improved turn time by 0.10 seconds and increased kick strokes by 5 kicks.
Mah et al. (2011) investigated the effects of additional sleep on 11 male college basketball players who, for the first 2-4 weeks of the study, maintained their normal sleep schedules. The players were tested on 282-foot agility sprint tests (baseline to half court and back to baseline, and then to full court and back to baseline), number of successful free throws out of 10, 3-point field goals out of 15, and a performance self-rating during and after practices and games. Testing was followed by a 5- to 7-week sleep extension period, during which subjects obtained as much nighttime sleep as possible, with a minimum goal of 10 hours in bed each night.
After the sleep extension, the players’ timed agility sprint improved by 0.07 seconds; their free-throw percentage increased by 9%; and their 3-point field goal percentage improved by 9.2%. Subjects’ self-ratings during/after practices (1-10) improved from 6.9 to 8.8, and self-ratings during/after games improved from 7.8 to 8.8.
Mah and colleagues also studied seven Stanford University football players. For 2 weeks the football players kept to their normal sleeping schedules. The players then aimed for a minimum of 10 hours of sleep each night. They were tested before and after the sleep extension, and their 20-yard shuttle run times decreased by 0.10 seconds on the second round of tests. Forty-yard dash times also decreased by 0.10 seconds, and daytime sleepiness and fatigue scores fell significantly. Vigor scores dramatically improved (AASM 2010).
Samuels (2009) indicated that critical metabolic and immune processes occur during specific stages of sleep. Therefore, a critical relationship exists between physical recovery during sleep and an athlete’s ability to train at maximum capacity with optimal results.
Walker and Stickgold (2006) have shown there is a relationship among sleep, consolidation of skill memory and performance enhancement, concluding that sleep restriction poses a risk to sleep-dependent memory consolidation and neural plasticity (strengthening or weakening nerve connections or adding new nerve cells based on outside stimuli). Thus, a causal relationship exists among sleep, memory and performance. This finding demonstrates that adequate sleep is important for ensuring optimal performance in athletes when cognitive tasks and psychomotor vigilance are required.
A growing body of research suggests that paying attention to the body clock (circadian rhythm), and its effects on energy and alertness, can help determine the different times of day when most of us perform our best at specific tasks, from resolving conflicts to thinking creatively. Physical performance is usually best, and risk of injury least, between 3:00 pm and 6:00 pm (Smolensky and Lamberg 2001). Muscle strength tends to peak between 2:00 pm and 6:00 pm–at levels as much as 6% above the day’s lows–thus improving our ability to grip a club or racquet during those hours. Eye-hand coordination is best in late afternoon, making this a good time for racquet sports or coordination drills. Joints and muscles are as much as 20% more flexible in the evening, which may help a person work out harder or improve performance (Smolensky & Lamberg 2001).
A Universal Recovery Strategy
In the fitness industry, we talk about the importance of recovery after games and training, and we recommend many strategies, such as ice baths, chocolate milk, massage, foam rollers and recovery drinks. However, getting proper sleep–by improving sleep performance and taking naps–is an important recovery strategy that is missing from many training programs. The challenge may lie in finding a balance between overload and compensation. In other words, we need to find the mix of training and recovery that will promote regeneration and adaptation while including acute rest, chronic rest and, of course, sleep.
Gordon Sleivert, PhD, former vice president of sport performance at the Canadian Sport Centre Pacific, calls sleep “a universal recovery strategy that is essential to both physiological adaptation and to the consolidation of skill development.”
Improvements in fitness and sports performance depend on a combination of several factors, including exercise, nutrition, hydration and spiritual fulfillment/personal growth. With the emerging evidence about the importance of shuteye, fitness professionals must consider sleep a key part of any training program.