Sleep and Circadian Rhythm Disruption in Social Jetlag and Mental Illness - Progress in Molecular Biology and Translational Science - page 330

Local time (h)

18:00 22:00 2:00 6:00 10:00 14:00 18:00

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Mid-sleep on f ree days
(MSF)

Social jetlag = Δ MS (h)

Mid-sleep on workdays
(MSW)

Figure 11.4 Social Jetlag. Six-week long sleep-log of an extremely late chronotype

(MSF 7 a.m.), exemplifying the typical scalloping between sleep time on workdays

(black bars) and on weekends (white bars). Local time is indicated at the top of the graph
and the consecutive days of the sleep-log on the left. The difference between the mid-
sleep point on free days (MSF) and that on workdays (MSW) is used to quantify the
amount of “social jetlag.” Note that sleep on workdays in this late type is interrupted
by the alarm clock (constant sleep end at around 7 a.m., corresponding to the MSF point
of this subject). Although this is an extreme example of social jetlag (due to the late
chronotype in combination with an early work start), the majority of the population
shows similar patterns. Redrawn after Ref. 2 .