Good sleep is a prerequisite for optimal performance.1 Given that people spend about one-third of their lives asleep, sleep has substantial functions for development, daily functioning, and health.2 Perhaps no daytime behavior has been associated more closely with improved sleep than exercise.3 Researchers have shown that exercise serves as a positive function for sleep. Regular exercise consistently has been associated with better sleep.4 Moreover, the American Academy of Sleep Medicine considers physical exercise to be a modality of nonpharmacologic treatment for sleep disorders.4 When studying the influence of exercise on sleep, most investigators have compared acute exercise and sedentary control treatments.5 In their study of chronic moderate-intensity endurance exercise, Driver and Taylor6 also provided compelling evidence that exercise promotes sleep.
However, exercise can negatively affect sleep quality. Exercising immediately before going to sleep is detrimental to sleep quality.7 Athletes train very hard to improve their on-field performances, but excessive training may lead to a decrease in performance, which is known as overtraining syndrome. Researchers8 have shown that symptoms of overtraining indicate poor-quality sleep. Good sleep is an important recovery method for prevention and treatment of overtraining in sport practice.9
Evidence is compelling that chronic exposure to bright light (3000 lux) can enhance sleep.10 Guilleminault et al11 suggested that the effects of exposure to light may be more powerful than those associated with exercise. In a recent study in which red-light therapy (wavelength = 670 nm, light dose = 4 J/cm2) was used, Yeager et al12 indicated that red light could restore glutathione redox balance upon toxicologic insult and enhance both cytochrome c oxidase and energy production, all of which may be affected by melatonin. Melatonin is a neurohormone that is produced by the pineal gland and regulates sleep and circadian functions.13 No one knows whether sleep is regulated by melatonin after red-light irradiation in athletes. Researchers14,15 have demonstrated that phototherapy improves muscle regeneration after exercise. Red light could protect human erythrocytes in preserved diluted whole blood from the damage caused by experimental artificial heart-lung machines. However, the effect of red-light illumination on endurance performance is a new topic in sport science.
Sleep quality can be defined subjectively by self-report or by more objective measures, such as polysomnography or actigraphy. Subjective sleep quality has been assessed most widely with the Pittsburgh Sleep Quality Index (PSQI). The PSQI is a comprehensive 18-item self-report questionnaire assessing sleep disturbances in the previous month. It derives ordinal scores for 7 clinically relevant domains of sleep: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances (eg, awakenings from sleep due to discomfort, bad dreams), use of sleeping medication, and daytime dysfunction (feeling sleepy during the day due to a poor night's sleep). Scores from these separate components are combined to derive a global measure of sleep quality.
As demonstrated in these studies, acute or chronic exercise may lead to good- or bad-quality sleep. However, the effects of red light on sleep quality and endurance performance have not been investigated sufficiently. Therefore, the purpose of our study was to determine the effect of red light on the sleep quality and endurance performance of Chinese female basketball players.
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