Impact of Mandatory Wake Time on Sleep Timing, Sleep Quality and Rest-Activity Cycle in College and University Students Complaining of a Delayed Sleep Schedule: An Actigraphy Study

Figures & data

Table 1 Characteristics of the Participants

Variable	Delayed Subjects	Control Subjects	p-value	d
N	14	14
Age (y)	21.3 ± 1.2	22.1 ± 2.5	0.30
Gender (M,F)	6,8	6,8	N/A
MEQ score	38.6 ± 9.2	54.1 ± 4.8	< 0.001	2.11
PSQI score	4.7 ± 1.7	3.1 ± 2.3	0.053	0.76
Habitual bedtime (screening) (h:min ± min)	01:30 ± 76	23:23 ± 16	N/A	—
[range]	[00:19–04:49]	[22:51–23:54]
Social jet lag (screening questionnaire) (h)	2.4 ± 1.1	1.4 ± 0.7	0.01	1.08
[range]	[1.2–4.1]	[0.5–2.6]
Target bedtime (h:min ± min)	01:36 ± 74	23:15 ± 14	N/A	—
[range]	[00:30–04:00]	[23:00–23:45]
DLMO (h:min ± min)	23:03 ± 87	21:13 ± 60	0.001	1.47
Interval DLMO-TB (h)	2.5 ± 1.0	2.0 ± 0.9	0.19	0.53

Notes: Means (±SD) are shown. Group differences assessed using independent samples t-tests and effect size (d).

Abbreviations: MEQ, Morningness-Eveningness Questionnaire; PSQI, Pittsburgh Sleep Quality Index; DLMO, dim light melatonin onset; TB, target bedtime; N/A, not applicable (inclusion criteria).

Table 2 Actigraphic and Subjective Sleep Variables in the Two Groups of Participants

Sleep Variable	Delayed Subjects (n=13)	Control Subjects (n=13)	p-value	d
Bedtime (h:min ± min)	01:36 ± 64	23:38 ± 29	< 0.001	2.42
Sleep onset (h:min ± min)	01:48 ± 65	00:00 ± 36	< 0.001	2.04
Sleep offset (h:min ± min)	09:13 ± 80	07:59 ± 57	0.01	1.05
Duration of sleep episode (h)	7.4 ± 0.8	8.0 ± 0.8	0.08	0.70
Total sleep time (min)	394 ± 53	419 ± 61	0.48	0.44
Sleep efficiency (%)	88.8 ± 4.4	87.0 ± 5.7	0.39	0.34
Sleep onset latency (min)	11.7 ± 6.7	21.6 ± 15.0	0.09	0.02
Subjective sleep quality (score)	4.2 ± 0.5	4.0 ± 0.6	0.22	0.49
Subjective alertness on awakening (score)	3.6 ± 0.6	3.9 ± 0.6	0.26	0.45
Subjective alertness during the day (score)	3.9 ± 0.5	4.1 ± 0.5	0.35	0.37

Notes: Means (±SD) are shown. Subjective scores from 1 to 5; higher scores reflect better sleep or alertness quality. Group differences assessed using independent samples t-tests and effect size (d).

Table 3 Actigraphic Sleep Variables for the Nights with Free or Mandatory Wake Times, in the Two Groups of Participants

Sleep Variable	Delayed Subjects (n=11)	Control Subjects (n=11)	ANOVA Group x Night p-value (ηp^2)
	Mean ± SD	Mean ± SD	Group	Night	Interaction GxN
Bedtime (h:min ± min)
Free WT	01:22 ± 71	23:45 ± 25	< 0.001	0.50	0.23
Mandatory WT	01:33 ± 66	23:42 ± 31	(0.53)	(0.02)	(0.07)
Sleep onset (h:min ± min)
Free WT	01:33 ± 73	00:13 ± 31	< 0.001	0.76	0.10
Mandatory WT	01:42 ± 65	00:00 ± 38	(0.45)	(0.01)	(0.13)
Sleep offset (h:min ± min)
Free WT	09:32 ± 80	08:14 ± 54*	0.05	0.12	0.05
Mandatory WT	08:52 ± 82	08:19 ± 38	(0.19)	(0.12)	(0.18)
Duration of sleep episode (h)
Free WT	8.0 ± 1.1	8.0 ± 1.1	0.13	0.27	0.01
Mandatory WT	7.2 ± 1.1	8.4 ± 0.7**	(0.11)	(0.06)	(0.30)
Total sleep time (min)
Free WT	426 ± 62	417 ± 77	0.36	0.25	0.01
Mandatory WT	378 ± 82	439 ± 53*	(0.04)	(0.07)	(0.32)
Sleep efficiency (%)
Free WT	88.8 ± 3.8	86.4 ± 6.7	0.54	0.76	0.39
Mandatory WT	87.7 ± 7.8	87.0 ± 6.2	(0.01)	(0.02)	(0.04)
Sleep onset latency (min)
Free WT	11.1 ± 7.1	28.5 ± 19.3	0.35	0.02	0.34
Mandatory WT	8.9 ± 3.4	18.3 ± 15.3	(0.05)	(0.23)	(0.04)

Notes: Simple effect analysis: *p≤ 0.05, **p≤ 0.01, delayed vs controls.

Abbreviations: WT, wake time; η_p², partial eta-squared effect size.

Table 4 Subjective Estimates of Sleep and Alertness Quality for the Nights with Free or Mandatory Wake Times, in the Two Groups of Participants

Subjective Variable	Delayed Subjects (n=11)	Control Subjects (n=11)	ANOVA Group x Night p-value (ηp^2)
	Mean ± SD	Mean ± SD	Group	Night	Interaction GxN
Sleep quality before
Free WT	4.5 ± 0.4	4.0 ± 0.7	0.47	0.03	0.50
Mandatory WT	4.0 ± 0.7	3.9 ± 0.8	(0.08)	(0.22)	(0.03)
Alertness on awakening
Free WT	4.2 ± 0.4***	4.0 ± 0.6	0.46	<0.001	0.003
Mandatory WT	3.1 ± 0.8	3.8 ± 0.8	(0.03)	(0.64)	(0.37)
Daytime alertness after
Free WT	4.0 ± 0.5	4.0 ± 0.6	0.52	0.77	0.12
Mandatory WT	3.7 ± 0.6	4.1 ± 0.6	(0.02)	(<0.01)	(0.12)

Notes: Subjective scores from 1 to 5; higher scores reflect better sleep or alertness quality. Two participants in each group did not have free WT during their week of sleep diaries. Simple effect analysis: ***p<0.001, free vs mandatory WT.

Abbreviations: WT, wake time; η_p², partial eta-squared effect size.

Table 5 Rest-Activity Cycle Variables in the Two Groups of Participants

Variables	Delayed Subjects (n=13)	Control Subjects (n=13)	p-value	d
IS	0.48 ± 0.07	0.51 ± 0.08	0.36	0.36
IV	0.74 ± 0.19	0.85 ± 0.27	0.23	0.49
L5	15.6 ± 12.8	16.7 ± 12.2	0.83	0.08
M10	320.7 ± 78.9	405.6 ± 84.8	0.01	1.04
AMP	305.1 ± 73.2	389.0 ± 80.5	0.01	1.09

Notes: Means (±SD) are shown. Group differences assessed using independent samples t-tests and effect size (d). 13 subjects per group (missing data for one woman in each group).

Abbreviations: IS, interdaily stability; IV, intradaily variability; L5, activity in the low active 5 h; M10, activity in the high active 10 h; AMP, activity amplitude.

Figure 1 Rest-activity profiles (hourly means + sem) averaged over the 7 days of activity recording for the delayed (black circles) and control (open circles) subjects. Asterisks indicate significant differences (p≤ 0.05) between the two groups after FDR correction.

Table 6 Activity Levels and Estimated Amplitude for the Nights with Free or Mandatory Wake Times, in the Two Groups of Participants

Rest-Activity Cycle Variables	Delayed Subjects (n=11)	Control Subjects (n=11)	ANOVA Group x Night p-value (ηp^2)
	Mean ± SD	Mean ± SD	Group	Night	Interaction GxN
L5
Free WT	15.8 ± 17.4	15.8 ± 13.5	0.58	0.16	0.58
Mandatory WT	27.9 ± 29.5	21.2 ± 14.8	(0.02)	(0.10)	(0.02)
M10
Free WT	287 ± 68	428 ± 85***	0.006	0.58	0.04
Mandatory WT	329 ± 127	403 ± 69	(0.32)	(0.02)	(0.19)
AMP
Free WT	271 ± 61	413 ± 82	0.004	0.99	0.10
Mandatory WT	301 ± 133	382 ± 64	(0.35)	(<0.001)	(0.13)

Notes: Two participants in each group did not have free WT during their week of sleep diaries. Simple effect analysis: ***p= 0.001, delayed vs controls.

Abbreviations: WT, wake time; L5, activity in the low active 5 h; M10, activity in the high active 10 h; AMP, activity amplitude; η_p², partial eta-squared effect size.

Figure 2 Illustration of the rest-activity cycle (hourly means + sem) for days with mandatory (open circles) or free (black circles) wake times, in the groups of delayed (left panel) and control (right panel) participants.