Sleep is critical to normal physiological and psychological function, and people spend nearly one third of their lives asleep. Usual sleep duration is considered to be between 7 and 9 hours per night for healthy adults. The different stages of sleep have historically been defined according to the 1968 classification rules of Alan Rechtschaffen and Anthony Kales (R&K) as wakefulness, one of four stages of non-rapid eye movement (NREM) sleep (S1, S2, S3, and S4), or rapid eye movement (REM) sleep. The American Academy of Sleep Medicine (AASM) modified these standard guidelines and recommended that NREM sleep be referred to as N1, N2, and N3, with N3 reflecting R&K stages S3 and S4, and Stage REM to be referred to as Stage R. A normal sleep cycle (consisting of all the sleep stages) lasts for approximately 90 minutes and is repeated throughout the night.
Sleep can be measured by several different methods. Self-reports such as sleep logs or diaries are helpful to determine trends over time. However, these are subjective and rely on accurate recollection by the individual. Actigraphy is a method of measuring body movement. For the purpose of measuring sleep, these devices are typically worn on the wrist and periods of low activity scored as “sleep” and periods of high activity scored as “awake.” Due to its noninvasive nature, actigraphy has been used widely as a tool to measure sleep quantity and quality over lengthy periods of time and in the normal (home) sleeping environment, although the method cannot determine the different stages of sleep or transient arousals from sleep. Polysomnography is acknowledged as the gold standard method of measuring sleep, as it allows assessment of all sleep stages and is used widely to assess the presence and severity of sleep disorders. Polysomnography requires many electrodes to be attached to the scalp and face in order to measure brain, eye, and chin muscle activity, and sensors on the chest, finger, and face to monitor cardiorespiratory parameters.
Effects of Acute Exercise on Sleep
Normally, core body temperature peaks in the early evening, starts decreasing prior to bedtime, and reaches its minimum in the early hours of the morning. Exercise in the evening is known to raise core temperature, which could potentially oppose the normal pre-bedtime decrease and interfere with sleep onset. This is one factor underlying the current recommendations that exercise should only be performed 5 to 6 hours before bedtime and no closer than 3 hours prior to sleep. However, data supporting this widely accepted recommendation are scarce. Indeed, a study reported that high-intensity exercise performed in the evening has little effect on sleep in healthy young people. Similarly, a meta-analysis of the literature on the effect of exercise on sleep, accounting for time of day, showed that acute exercise increased Stage 2 and slow wave sleep, decreased REM sleep, and increased total sleep time.
Effects of Chronic Exercise on Sleep
There is little research investigating the effect of chronic exercise among athletes on sleep, although it has been reported that those athletes who become overtrained report disrupted sleep patterns. In the general population, regular physical exercise is recommended as a way to reduce the effects of other contributing factors to poor sleep such as smoking, ingesting too much caffeine, overeating, and consuming alcohol.
Effects of Acute Sleep Loss on Exercise
Good sleep is considered essential for optimum athletic performance and is regarded as the primary method of recovery from physical activity (PA). Acute sleep deprivation has been shown to negatively impact sport performance. However, the magnitude of this detrimental effect appears to depend on the specific athletic activity. A literature review by Thomas Reilly and Ben Edwards concluded that the effects of acute sleep deprivation or an altered sleep pattern had a marginal impact on predominantly aerobic or anaerobic sports (e.g., sprints, power events, running 3,000 meters, swimming 400 meters) but a negative impact on sports that required high concentration, consisted of a mixture of anaerobic and aerobic activities, or required multiple anaerobic efforts (e.g., field sports, sailing, road cycling, aiming sports, combat sports, swimming, middle distance running, jumping events, weight training). The specific performance decrements included poorer decision making (DM), increased errors, decreased power output, and increased fatigue.
Effect of Chronic Sleep Loss on Exercise
Very little is known about the effects of chronic sleep loss on athletic performance. Case studies of ultraendurance cycling events, which require sustained periods of wakefulness, report that, in order to maintain optimal athletic performance, at least 2 hours of sleep per night are required. Similarly, a cluster napping technique (multiple short naps) is reportedly adopted in ultraendurance sailing to achieve an average total sleep time of 5.5 hours per day, presumably as a method to maintain optimal vigilance.
Jet Lag and Exercise
One of the most common transient sleep disorders experienced by athletes is jet lag due to travel across multiple time zones. Symptoms of jet lag include disorientation, light-headedness, impatience, and lack of energy. Westward travel tends to be accompanied by less severe jet lag than eastward travel. Athletic performance can be compromised due to jet lag as the body’s circadian rhythms adjust to the new time zone.
Undiagnosed Sleep Disorders and Exercise
Undiagnosed sleep disorders have the potential to reduce athletic performance. One such prevalent disorder among the general population is obstructive sleep apnea (OSA), which is characterized by repetitive narrowing and/or collapse of the pharyngeal airway during sleep, resulting in reduced blood oxygen levels and multiple arousals from sleep. The repetitive arousals fragment sleep and have been associated with decreased motor function and increased fatigue. While usually associated with a sedentary lifestyle and obesity, anatomically predisposed athletes (e.g., high body mass index and large neck circumference) can also be affected by OSA. One example of this is the increased prevalence of OSA among American football players, particularly offensive and defensive linemen.
Sleep is critical to both physiological and psychological function. Sleep loss has a negative impact on athletic performance; hence, education of athletes and coaches on sleep hygiene principles is needed to minimize sleep loss-related performance decrements. Sleep disorders are surprisingly common among athletes and, if suspected, should be investigated and treatment initiated in order to optimize athletic performance.
- Atkinson, G., & Davenne, D. (2007). Relationships between sleep and physical activity and human health. Physiology and Behaviour, 90, 229–235.
- Driver, H. S., & Taylor, S. R. (2000). Exercise and sleep. Sleep Medicine Reviews, 41, 387–402.
- Reilly, T., & Edwards, B. (2007). Altered sleep-wake cycles and physical performance in athletes. Physiology and Behaviour, 90, 274–284.
- Youngstedt, S. D. (2005). Effects of exercise on sleep. Clinics in Sports Medicine, 24, 355–365.
- Youngstedt, S. D., O’Connor, P. J., & Dishman, R. K.(1997). The effects of acute exercise on sleep: A quantitative synthesis. Sleep, 20(3), 203–214.