Introduction
Sufficient sleep is necessary for mental and physical health, serving recovery and well-being. It increases daytime concentration, cognitive function and regulates emotionsDuration of sleep and therefore, sleep efficiency (total sleep time divided by time in bed) influence parameters of cardiac autonomic nervous system regulationIn our study we used an experimental design to evaluate and compare two specific sleep interventions, sleep fragmentation and sleep restriction. The aim was to investigate how these two types of intervention affect the cardiac autonomic tone. We hypothesized: Sleep restriction has a greater effect on heart rate and its variability during the night than sleep fragmentation; and a night with sleep restriction or sleep fragmentation shows higher sympathetic activity during night (indicating increased autonomic stress) than a night with undisturbed sleep.Therefore, we assessed heart rate and its variability as the common marker of sympathetic and vagal activity.