Effect of morning exercise in sunlight on the sleep-wake cycle in adolescents

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.

Effect of Partial Sleep Deprivation on Auditory Event Related Potential and Reaction Time in Medical Students.

The aim of the present study was to evaluate the effects of partial sleep deprivation on the cognitive status and alertness of medical students using auditory event related potential (ERP) and auditory reaction time (RT) using sleep questionnaire, Stanford Sleepiness Scale (SSS), auditory ERP (P300) and RT. Sleep time was significantly shorter in the test condition as compared to the baseline values (p<0.001). Significantly higher values on the SSS (p<0.05) were found after sleep restriction. The P300 latency and amplitude significantly decreased (p<0.01 and p<0.001 respectively) when the test values were compared to the baseline. RT also showed a significant decrease (p<0.001) in the test condition as compared to the baseline values. However, no significant correlation could be ascertained between SSS and P300 amplitude and latency as well as RT. This study demonstrates that partial sleep deprivation produces variable effects on the cognitive status of medical students as reflected by the decrease in P300 amplitude and latency. Alertness of medical students seemed to show an improvement as reflected by the decrease in RT.