The delayed circadian timing of adolescents creates a conflict with early school start times (SSTs). We used wrist actimetry to compare sleep parameters and routine nighttime activities in middle school students attending either a morning (0700 to 1200 h) or an afternoon (1230 to 1730 h) school shift. On school days, students from both shifts (n = 21 for morning shift, n = 20 for afternoon shift, ages 12-14 years) had a similar sleep onset, but morning-shift students had an earlier sleep offset and a 1 h 45 min shorter sleep duration than their afternoon peers, who slept the recommended 8 to 10 h of daily sleep. Only morning-shift students had afternoon naps, but this afternoon sleep was not sufficient to overcome sleep deprivation. On weekends, sleep onsets and offsets did not differ between shifts. Because only morning-shift students woke up later and slept longer (2 h 3 min) on weekends, they were also the only ones who experienced social jetlag. Daily surveys on their nighttime (from 1800 to 0600 h) activities indicated there was no difference between shifts in the time spent on leisure or using electronic media during school days, but students from both shifts spent more time in these activities during the weekend. Our study confirms that early SST in adolescents is associated with sleep deprivation and suggests that schedules that start much later than typically considered may be needed to eliminate sleep deprivation in adolescents.

青少年的昼夜节律时间延迟会与早期入学时间（SST）产生冲突。我们使用腕部活动度法比较了上早班（0700至1200小时）或下午（1230至1730小时）上学的中学生的睡眠参数和常规夜间活动。在上学日，两个班次的学生（早上班次n = 21，n下午班= 20，年龄在12-14岁之间）有类似的睡眠发作，但早上班学生比下午的同龄人睡得更早，睡眠时间短了1小时45分钟，而同龄人则睡了8至10小时日常睡眠 只有早班学生有午睡，但今天下午的睡眠不足以克服睡眠不足的问题。在周末，轮班之间的睡眠发作和偏移没有差异。因为只有晨班学生才醒得更晚，周末睡得更长（2小时3分钟），所以他们也是唯一经历过社交时差的人。对他们夜间（从1800小时到0600小时）活动的每日调查表明，在上学期间休闲或使用电子媒体的时间上的变化没有差异，但是两个班次的学生在周末都花了更多时间在这些活动上。我们的研究证实，青少年早期SST与睡眠剥夺有关，并建议可能需要比通常认为要晚得多的时间表开始，以消除青少年的睡眠剥夺。