Abstract
A delay in bedtime occurs in adolescence compared with childhood. However, the early waking that morning school hours impose leads to partial sleep deprivation. Although exposure to light is the most important regulator of circadian rhythm in mammals, physical exercise influences circadian synchronization. To assess the effect of morning physical exercise in sunlight on the sleep-wake cycle (SWC) in adolescents, 160 first- and second-year high-school students were exposed to classes in their usual classroom (Group C) or in a swimming pool exposed to sunlight (Group E) while physically exercising (EE; i.e., swimming) or resting (EL). At baseline, we applied Health and Sleep and Horne & Ostberg chronotype assessment questionnaires. One week later and during the intervention, we applied the Sleep Diary and Karolinska Sleepiness Scale. During the intervention we observed no changes in bedtime, time in bed and in indices of irregularity of bedtime and wake-up time. The changes observed in wake-up time (i.e., a delay in the EE group on Saturday), sleep quality (i.e., an improvement), and sleepiness (i.e., an increase) were also observed in the control group, discarding an intervention effect. We suggest that morning physical exercise in sunlight had no effect on SWC parameters, sleep quality, or daytime sleepiness, possibly because of the large irregularity in the SWC between weekdays and weekends in adolescent students as well as the low frequency and duration of exercise during the intervention. Therefore, studies that evaluate a higher frequency or duration of exercise are needed to assess its effect on the SWC in adolescents.
Highlights
Adolescence is characterized by innumerable transformations such as a delay in bedtimes and wakeup times compared with childhood and adulthood and a greater need for sleep compared with adulthood
The sleep-wake cycle (SWC) profiles that we found among students at baseline were similar to those observed in Brazilians (Andrade et al, 1993; Louzada & Menna-Barreto, 2003; Sousa et al, 2007), Americans (Shinkoda, Matsumoto, Park, & Nagashima, 2000; Iglowstein, Jenni, Mollinari, & Largo, 2003), and Italians (Giannotti & Cortesi, 2002)
The students showed later and longer nocturnal sleep on weekends and earlier and shorter nocturnal sleep on weekdays, confirming the SWC irregularity characteristic of students who study in the morning (Andrade et al, 1993; Wolfson & Carskadon, 1998; Shinkoda et al, 2000; Giannotti & Cortesi, 2002; Iglowstein et al, 2003)
Summary
Adolescence is characterized by innumerable transformations such as a delay in bedtimes and wakeup times compared with childhood and adulthood and a greater need for sleep compared with adulthood This delay has long been considered a psychosocial modification that results from the lifestyle during this phase, characterized by increased socialization (Carskadon, 2002; Carskadon & Acebo, 2002) and reinforced by other social factors such as decreased parental discipline with regard to bedtime (Carskadon, 2002), extracurricular employment (Teixeira et al, 2007), and increased school activities (Carskadon, 2002). A change in sensitivity to light may occur that decreases in the morning and increases later in the day
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