Physical exercise is perceived as fundamental for the promotion and maintenance of health and quality of life. Regular physical exercise is associated with reduced risk of all-cause mortality, reduced risk of developing cardiovascular and metabolic diseases, improved immune system, reduced levels of depression and anxiety, reduced pain, among othersPIERCY; TROIANO; BALLARD; CARLSON et al., 2018The American College of Sports MedicineAmerican College of Sports Medicine -ACSM) recommends at least 150 minutes of moderate aerobic physical exercise or 75 minutes of vigorous aerobic physical exercise for adults and the elderly as a minimum weekly recommendationMEDICINE, 2013In addition, a minimum of 2 days is established for the development of strength and muscular endurance. However, it is worth mentioning that this recommendation is intended only for the promotion and maintenance of basic health, so that people who want changes in body composition, as well as development of physical performance, will benefit from greater volumes and intensities of trainingMEDICINE, 2013).
Given its complexity and variety of benefits in the body, the objective of this article is to elucidate the effects of physical exercise on aspects related to sleep. Initially, the effects on sleep variables will be presented and, then, evidence demonstrating the effects of exercise on sleep disorders. Finally, some mechanisms proposed as responsible for the effects observed in sleep after physical exercise will be presented. The description of the effects of acute and chronic physical exercise was based on the systematic review conducted by Kredlow et al.KREDLOW; CAPOZZOLI; HEARON; CALKINS et al., 2015).
Acute physical exercise
Studies that evaluated the effect of acute physical exercise point to greater total sleep time, sleep efficiency, and duration of slow-wave sleep. In addition, on days in which there was physical exercise, the latency to sleep onset was reduced. Not only, time awake after sleep onset and proportion of stage 1 sleep were lower after physical exercise.
Regular physical exercise
Similar to the effects of acute physical exercise, studies that evaluated the effects of regular physical exercise on sleep found greater total sleep time and sleep efficiency in individuals who performed physical exercise, compared to individuals allocated to control groups. Sleep onset latency was also lower in physical exercise practitioners. Finally, there was a better perception of sleep quality after regular physical exercise. Most of the available studies used the Pittsburgh Sleep Quality IndexPittsburgh Sleep Quality Index – PSQI) (BERTOLAZI; FAGONDES; HOFF; DARTORA et al., 2011; BUYSSE; REYNOLDS; MONK; BERMAN et al., 1989) to assess the sleep quality of the participants. This questionnaire contains seven subscales (daytime sleepiness, sleep disturbances, sleep duration, sleep efficiency, sleep latency, medication use, and subjective sleep quality). The practice of regular physical exercise showed improvements in all subscales, except the use of medication.
Effects of physical exercise on sleep disorders
A study conducted by Passos et alPASSOS; POYARES; SANTANA; GARBUIO et al., 2010evaluated and compared the effect of three modalities of acute physical exercise in patients with chronic primary insomnia. Patients were randomized into four groups: moderate-intensity aerobic exercise, high-intensity aerobic exercise, moderate-intensity resistance exercise, and control. Patients' sleep was assessed using polysomnography. Only the group that performed moderate aerobic exercise showed statistically significant changes in the parameters sleep onset latency (55% decrease), total sleep time (18% increase), and sleep efficiency (13% increase). In addition, the researchers also assessed the patients' mood level, and the group that performed moderate-intensity aerobic exercise showed a reduction in the level of anxiety.
Positive results after physical exercise were also observed for movement disorders during sleep. De Mello et alDE MELLO; LAURO; SILVA; TUFIK, 1996evaluated 11 volunteers with complete spinal cord injury between T7 and T12. The volunteers underwent a maximal exercise test, and sleep was assessed using polysomnography. It was observed that the sleep pattern improved significantly the night following the maximal exercise test. Specifically, the occurrence of periodic leg movements and restless legs syndrome was reduced after exercise. Years later, De Mello and colleagues evaluated the effect of chronic aerobic exercise (45 days of moderate-intensity aerobic training performed three times a week and average duration of 30 minutes per session) on the same parameters, and the results were similar, suggesting that a physical exercise protocol has the potential to reduce the incidence of movement disorders during sleepDE MELLO; SILVA; ESTEVES; TUFIK, 2002).
Responsible mechanisms
Several mechanisms have been proposed to explain the beneficial effects that physical exercise exerts on sleep. Among them, body temperatureMCGINTY; SZYMUSIAK, 1990change in cytokine concentrationSANTOS; TUFIK; DE MELLO, 2007increased energy consumption and metabolic rateMORSELLI; GUYON; SPIEGEL, 2012central nervous system fatigueUCHIDA; SHIODA; MORITA; KUBOTA et al., 2012changes in mood/anxietyBUMAN; KING, 2010; UCHIDA; SHIODA; MORITA; KUBOTA et al., 2012changes in heart rate and variability of heart rateSANDERCOCK; BROMLEY; BRODIE, 2005secretion of growth hormoneKANALEY; WELTMAN; VELDHUIS; ROGOL et al., 1997, secretion of brain-derived neurotrophic factoZAGAAR; DAO; LEVINE; ALHAIDER et al., 2013, better physical conditioningSHAPIRO; WARREN; TRINDER; PAXTON et al., 1984and changes in body compositionUCHIDA; SHIODA; MORITA; KUBOTA et al., 2012In addition, there are indications that the responsible mechanisms differ between acute and chronic physical exerciseUCHIDA; SHIODA; MORITA; KUBOTA et al., 2012).
Sleep pattern assessment
Actigraphy is a non-invasive technique that can be used to assess sleep pattern and sleep-wake rhythm. The actigraph is a wristwatch-like device that contains light, motion, and temperature sensors. Through this information, it is possible to extract data regarding variables such as total sleep time, latency to sleep onset, time awake after sleep onset, sleep efficiency, time awake and variables related to rhythm, such as cosinor, spectrogram, periodogram, and non-parametric variables such as L5, M10, IS and IV.
