Downloaded from www.sjweh.fi on September 02, 2011

Original article
Scand J Work Environ Health 2011;37(5):418-426
doi:10.5271/sjweh.3162
Weekend sleep intervention for workers with habitually shortsleep periods
by Kubo T, Takahashi M, Sato T, Sasaki T, Oka T, Iwasaki K
Affiliation: National Institute of Occupational Safety and Health, 6-21-1,
Nagao, Tama-ku, Kawasaki 214-8585, Japan. kubo@h.jniosh.go.jp
Refers to the following texts of the Journal: 2003;29(3):171-188
2008;34(3):213-223 2006;32(6):502-514 2006;32(4):318-327
Key terms: alertness; fatigue; performance; short sleep; sleep; sleep
debt; sleep intervention; sleepiness; weekend sleep extension

This article in PubMed: www.ncbi.nlm.nih.gov/pubmed/21475780

Print ISSN: 0355-3140 Electronic ISSN: 1795-990X Copyright (c) Scandinavian Journal of Work, Environment & HealthOriginal article
Scand J Work Environ Health 2011;37(5):418–426. doi:10.5271/sjweh.3162

Weekend sleep intervention for workers with habitually short sleep periodsby Tomohide Kubo, PhD,1 Masaya Takahashi, PhD,1 Tomoaki Sato, PhD,2 Takeshi Sasaki, MSc,1 Tatsuo
Oka, BA,1 Kenji Iwasaki, PhD 1
Kubo T, Takahashi M, Sato T, Sasaki T, Oka T, Iwasaki K. Weekend sleep intervention for workers with habituallyshort sleep periods. Scand J Work Environ Health 2011;37(5):418–426. doi:10.5271/sjweh.3162

Objective This study was conducted to determine whether extended sleep time during the weekend improvesalertness and performance during the subsequent week for workers who are habitually short on sleep time.

Methods Daytime employees in the manufacturing industry [38.3, standard deviation (SD) 8.1 years old, mean

weekday sleep ≤6 hours] participated in a study that lasted 3 successive weeks. Participants were instructed tostay in bed for ≥8 hours between 22:00–09:00 hours on weekends during the first week as a sleep intervention
condition and keep their habitual sleep–wake patterns as a habitual weekend sleep condition beginning the weekend of the second week through Thursday of the third week. Half the participants underwent the conditions in
one order and the other half in the reverse. Sleep was monitored by an actigraph. A psychomotor vigilance task,
subjective fatigue, and blood pressure were measured on Monday and Thursday during the afternoon each week.

Results Sleep duration on weekends was approximately 2 hours longer per day during the intervention. However, sleep duration during weekdays following the intervention returned to shorter periods. Significantly shorter
reaction times and a smaller number of lapses on the psychomotor vigilance task were found on Mondays after theintervention than after the habitual weekend sleep. The opposite results, however, were observed on Thursdays.

Conclusions Sleep extension on weekends may be effective in improving alertness and performance during
the first days in subsequent weeks among workers with short sleep times. These benefits might be maintained if
sufficient sleep duration continues.

Key terms alertness; fatigue; performance; sleepiness; sleep debt; weekend sleep extension.

Working overtime is common in developed countries
and has increased in recent years (1). Previous studies
have suggested an association between long working
hours and adverse health outcomes, such as insufficient
sleep, depression, and cardiovascular disease (2–4).
In particular, a great deal of research has focused on
the influence of overtime work on health problems inJapan (5–7).
Sleep plays an essential role in recovery from workrelated fatigue (8). Shortened sleep due to long working
hours or overtime may thus increase the likelihood of
insufficient recovery from fatigue (9–11) and stressrelated diseases (12–15). Therefore, an intervention toensure adequate sleep is required to protect workers’
health and well-being. A potential opportunity for suchan intervention is assumed to be available either during weekdays or on weekends. For example, it may beeffective to set a “no-overtime” day in the middle of theweek. Alternatively, an intervention on weekends would
be more feasible. Indeed, workers tend to extend their
sleep duration on weekends to compensate for sleep debt
accumulated between Monday–Friday (7).
A potential problem with attempting to sleep longer
on weekends involves circadian rhythms. Specifically,
delayed wake-up times on weekends have undesirable
effects on alertness and performance during the subsequent weekdays (eg, the Blue Monday phenomenon)(16, 17). These disadvantages need to be avoided, even
if a certain amount of weekend sleep (ie, sleep compensation) would be important to facilitate recovery fromwork-induced fatigue. Currently, little is known about
which factors (ie, sleep extension or sleep regularity)
should be prioritized for promoting fatigue recovery.
Given that daytime workers are likely to compensate for

1 National Institute of Occupational Safety and Health, Kawasaki, Japan.
2 Department of Management Design, Faculty of Business Administration, Osaka International University, Osaka, Japan.

Correspondence to: Tomohide Kubo, PhD, National Institute of Occupational Safety and Health, 6-21-1, Nagao, Tama-ku, Kawasaki 2148585, Japan. [E-mail: kubo@h.jniosh.go.jp]

418

Scand J Work Environ Health 2011, vol 37, no 5

Kubo et al

the sleep debt they accumulate throughout the week byextending their weekend sleep times at the expense of
sleep regularity (7), examining the costs and benefits ofextended sleep duration during weekends is crucial interms of occupational health. Unfortunately, to the bestof our knowledge, no research has examined the effects
of sleep extension during weekends among workers.
The present study was conducted to determine whether
sleep extension during weekends improves alertness
and performance during the subsequent weekdays forworkers with habitually short sleep times.

f­ igure 1). The participants were required to complete
two conditions (the intervention and the habitual weekend sleep condition). Half the participants underwent
the conditions in one order (eg, from the intervention
to the habitual weekend sleep condition) and the otherhalf underwent the conditions in the reverse. They
were instructed to stay in bed for ≥8 hours between
22:00–09:00 hours on the weekend (Friday, Saturday,
and Sunday) of the first week as a sleep intervention andto keep their habitual sleep–wake patterns as a control
beginning the weekend of the second week throughThursday of the third week.

Methods

Measurements

Participants
Before the study began, a questionnaire was distributed to402 employees working at an electric company in Kyoto
prefecture in order to select possible participants. The
respondents were given the morningness–eveningness
questionnaire (18) and asked about their habitual sleep
time during weekdays and weekends and their healthcondition (ie, whether they have been sick and whether
they take or have taken prescription medications). The
selection criteria for participants were set as (i) “neither
entirely morning nor evening type,” as evaluated by
the questionnaire, (ii) <6 hours mean sleep duration on
weekdays, and (iii) taking no prescription medications.
Consequently, 49 respondents who met the selection criteria were recruited. Of these, 28 employees [mean 38.8,
standard deviation (SD) 8.5 years old, 18 men and 10
women] who were able to attend all sessions of the study
were selected as participants. However, two participants
withdrew from the study, citing job requirements andunexpectedly poor health conditions, respectively (mean38.3, SD 8.1 years old, 18 men and 8 women). Regarding
their social status, 23 participants cohabited with someone, whereas 2 participants lived alone (1 participant did
not answer). Additionally, their weekly working hours in
the past month were 35–40 hours for 34.6% (N=9), 41–50
for 42.3% (N=11), 51–60 for 19.2% (N=5), and 61–70 for
3.8% (N=1). Before the study began, the participants were
provided with an information sheet outlining the goals of
the study and were given the opportunity to ask questions.
The Research Ethics Committee of the National Instituteof Occupational Safety and Health, Japan, approved thisstudy. All participants gave written informed consent andreceived payment for their participation.
Study design
This study lasted three successive weeks (from Mondayof the first week to Thursday of the third week; see

A battery of tests, which consisted of a psychomotor
vigilance task, self-rated fatigue symptoms, and bloodpressure, was used to measure the effects of the study
conditions.
The psychomotor vigilance task is a sustainedattention reaction time task with a random interstimulus interval of 2–10 seconds (PVT-192, Ambulatory
Monitoring, Ardsley, New York, USA) (19). Lapses(reaction times >500 milliseconds) were counted during each 10-minute test as a measure of performance
impairment indicative of reduced behavioral alertness.
The data were analyzed for speed (1/reaction time ×1000) and transformed lapses (square root transform[SQR(lapses)+SQR(lapses+1)]).
Subjective fatigue symptoms were assessed by aquestionnaire that asked about work-related feelings offatigue Jikaku-sho shirabe (20), which was proposedby the Industrial Fatigue Research Committee of Japanese Occupational Health in 2002. This questionnaire
consists of 25 subjective fatigue symptoms that are
categorized into 5 factors of feeling: (i) drowsiness,(ii) instability, (iii) uneasiness, (iv) local pain or dullness, and (v) eyestrain. For each item, participants arerequested to estimate the intensity of their feelings
using the following scale: “totally disagree,” “agreescarcely,” “agree slightly,” “agree considerably,” and“agree strongly.” These five intensities were assigned
scores of 1–5 points, respectively.
The participants’ blood pressure (ES-P2100,
TERUMO Corporation, Tokyo, Japan) was measured
twice during each test. The mean of these measurements
was recorded.
Sleep was monitored by an actigraph (Micro-mini
RR, Ambulatory Monitoring, Ardsley, New York, USA)throughout the period of the study. The actigraph was
secured on the participants’ non-dominant wrist. Epochlength was set at 1-minute intervals. Sleep data wereanalyzed by Action-W® version 2.4.20 software (Ambulatory Monitoring, Ardsley, New York, USA) with theCole-Kripke algorithm (21). In this study, total sleep time
Scand J Work Environ Health 2011, vol 37, no 5419

Weekend sleep extension for alertness and performance

1st week

2nd week

3rd week

Intervention

Sleep
intervention

Baseline

Habitual weekend
sleepIntervention

Habitual weekend
sleep

Sleep
intervention

Figure 1. Study design (within-subject
design). In the sleep intervention condition, participants were instructed to stayin bed for ≥8 hours between 22:00–09:00
hours on weekends (Friday, Saturday, andSunday) of the 1st week (or 2nd week) as asleep intervention. Meanwhile, they wererequired to keep their habitual weekend
sleep patterns as a control on the weekendof the 2nd week (or 1st week), followed until
Thursday of the 3rd week.

Figure 1. Study design (Within-subject design). In the sleep intervention
condition, participants were instructed to stay in bed for 8 hours or more
between 22:00 and 9:00 on weekends (Friday, Saturday, and Sunday) of the
1st week(orefficiency,
2nd week) asa sleepand
intervention.
Meanwhile,
they wererequired(TST),
sleep
bedtime,wake time
were anaday]).
The main interest was in the interaction effect.
to keep
their habitual
weekendsleep patterns
as a control
on the weekendoflyzed
to assessthe qualityof sleep.
Sleep efficiency
was
Significant
interaction was assessed using post-hoc
the 2nd week (or 1st week), followed until Thursday of the third week.

calculated as: (ratio of TST to total time in bed) × (100).
Procedure

The present study lasted three weeks. Participants wererequired to follow their usual sleep–wake cycles in thefirst week as a baseline. In the intervention condition,
they were instructed to remain in bed for ≥8 hours
between 22:00–09:00 hours and prohibited from taking a daytime nap on weekends (Friday, Saturday, andSunday). The participants were encouraged to spend theweekends following the instructions as closely as possible. No other assistance was provided (eg, a telephone
reminder). In the habitual weekend sleep condition, participants were required to keep their habitual sleep–wakepatterns on the weekend.
The test battery was conducted on Monday andThursday during the afternoon in all three weeks. Participants were instructed to arrive at a testing room
between 14:00–15:00 hours. The order of measurements
was subjective fatigue (5 minutes), blood pressure (5minutes), and the psychomotor vigilance task (10 minutes). During the test period, participants were required
to switch off their cell phones and take off their wristwatches so that they could concentrate on the test. They
also practiced the psychomotor vigilance task for a few
minutes before each test period.
Data analysis
Data for the test battery and actigraph were analyzed
using two-way mixed-model analysis of variance(ANOVA). The ANOVA model consisted of subjects
as the random effect and the following fixed effects:
condition (sleep intervention versus habitual weekend
sleep) and day (test battery: 4 levels [Monday, Thursday,
Monday, Thursday] and actigraph: 7 levels [Monday,
Tuesday, Wednesday, Thursday, Friday, Saturday, Sun-

420

Scand J Work Environ Health 2011, vol 37, no 5

t-tests to reveal whether there was a significant difference between conditions. All statistical analyses were
performed using SPSS 17.0 for Windows (SPSS Inc,
Chicago, IL, USA).

Results
The results of mixed-model ANOVA for all measurements are presented in table 1.
Sleep
For sleep parameters, significant interactions wereobserved in TST and bedtime (F6,325=9.74, P<0.001
and F6,325=17.21, P<0.001, respectively; figure 2).
Post-hoc analyses showed that weekend sleep patterns
were significantly longer in TST and participants had
earlier bedtimes in the intervention than the habitual
weekend sleep condition (all P<0.05). However, nosignificant interaction was observed between sleep
efficiency and wake time. Regarding the main effectof condition, significant differences were observed in
TST (F1,325=44.56, P<0.001), bedtime (F1,325=50.47,
P<0.001), and wake time (F1,325=5.84, P=0.016), but
not sleep efficiency. The main effect of day was significant for TST (F6,325=23.64, P<0.001), sleep efficiency (F6,325=2.93, P<0.001), bedtime (F6,325=8.10,
P<0.001), and wake time (F6,325=51.62, P<0.001).
Sustained attention
Psychomotor vigilance task performance showedsignificant interactions in reaction times and lapses(F3,175=6.01, P=0.001 and F3,175=4.53, P=0.004,
respectively; figure 3). Significantly shorter reaction
times (P<0.05) and fewer lapses (P<0.05) were observed

Kubo et al

Table 1. Mixed-model analysis of variance results.
Mixed-model analysis of variance
Condition

Day

Interaction

F-valueP-value

F-valueP-value

F-valueP-value

Actigraphic sleep parameters a
Total sleep time
Sleep efficiency
Bedtime
Wake time

44.56
0.82
50.47
5.84

0.000
0.367
0.000
0.016

23.64
2.93
8.10
51.62

0.000
0.008
0.000
0.000

9.74
1.97
17.21
1.39

0.000
0.069
0.000
0.219

Psychomotor vigilance task b
Reaction time
Lapse

0.02
0.06

0.890
0.803

0.41
0.62

0.745
0.606

6.01
4.53

0.001
0.004

Subjective fatigue questionnaire b
Drowsiness
Eyestrain
Instability
Uneasiness
Local pain or dullness

2.90
0.18
0.09
0.24
0.00

0.090
0.670
0.759
0.627
0.988

4.29
6.14
11.54
7.84
2.44

0.006
0.001
0.000
0.000
0.066

1.81
0.34
0.18
0.08
0.02

0.148
0.794
0.910
0.971
0.995

1.21

0.274

13.62

0.000

1.69

0.171

0.01

0.906

2.38

0.071

0.24

0.869

Blood pressure b
Systolic blood pressure
Diastolic blood pressure

Condition=df(1,325); Day and Interaction=df(6,325).
b Condition=df(1,175); Day and Interaction=df(3,175).
aon Mondays following the intervention condition, as
compared with the habitual weekend sleep condition. In
contrast, the intervention condition showed significantly
longer reaction times and a larger number of lapses on
Thursdays than the habitual weekend sleep condition(P<0.05). No significant main effects of condition and
day were observed.
Subjective fatigue
No significant interactions were found between theintervention and the habitual weekend sleep condition in
any of the five subscales of the questionnaire for workrelated feelings of fatigue (figure 4). No significant main
effects of condition were observed for any of the fivesubscales. However, the main effects of day were significant for drowsiness (F3,175=4.29, P<0.001), eyestrain(F3,175=6.14, P=0.001), instability (F3,175=11.54,
P<0.001), and uneasiness (F3,175=7.84, P<0.001), but
not for local pain or dullness.
Blood pressure
The two parameters of blood pressure showed no significant interactions between the intervention and thehabitual weekend sleep condition (figure 5). No main
effects of condition were found for the two parameters.
The main effects of day were significant for systolicblood pressure (F3,175=13.62, P<0.001), but not fordiastolic blood pressure.

Discussion
The purpose of this study was to examine whether weekend sleep extension contributes to improved alertness
and performance during the following week among daytime workers with habitually short sleep duration. TST
for the intervention condition was 1–2 hours longer per
day than for the habitual weekend sleep condition (from
5–7 hours). However, TST during weekdays after theintervention again returned to 5 hours. Performance on
the psychomotor vigilance task significantly improvedon Monday after the intervention. Nevertheless, significantly longer reaction times and a larger number oflapses on the psychomotor vigilance task were observedon Thursday after the intervention than after the habitual
weekend sleep condition. With respect to subjective
fatigue and blood pressure, significant favorable effects
of sleep extension were not found. Taken together, thepresent findings suggest that sleep extension on weekends produced favorable influences on alertness andperformance during the first day of the subsequent week,though these benefits dissipated after that.
As expected, an improvement in alertness and performance was observed on the Monday following thesleep intervention. This finding agrees with previous
studies, which reported better neurobehavioral performance and less subjective sleepiness by recovery sleep
following shortened sleep protocols (22–24). However,these findings were inconsistent with the findings of
Scand J Work Environ Health 2011, vol 37, no 5

421

Weekend sleep extension for alertness and performance

8.0
7.5

Total sleep time (min)Mean± SE
N=26

*

7.0

*

*

6.5

27.0
Condition: P<0.001
Day: P<0.001
Interaction: P<0.001

26.5
25.5
25.0

5.5

24.5

5.0

24.0

4.5

23.5

100

Thu
/
Fri

Fri
/
Sat

Sat
/
Sun

Sun
/
Mon

Sleep efficiency (%)

Mon
/
Tue

Tue
/
Wed

Wed
/
Thu

9.0

95

*
Thu
/
Fri

Fri
/
Sat

*
Sat
/
Sun

Wake time (hr)

*

Sun
/
Mon

Mean± SE
N=26

Condition: P<0.001
Day: P<0.001
Interaction: P<0.001
Mon
/
Tue

Tue
/
Wed

Wed
/
Thu

Condition: P=0.016
Day: P<0.001
Interaction: P=0.219

8.5
8.0

90

7.5
7.0

85
80

23.0

9.5

Mean± SE
N=26

Mean± SE
N=26

26.0

6.0

4.0

Bedtime (hr)Condition: P=0.367
Day: P=0.008
Interaction: P=0.069
Thu
/
Fri

Fri
/
Sat

Sat
/
Sun

Sun
/
Mon

Mon
/
Tue

Tue
/
Wed

Wed
/
Thu

Sleep intervention

6.5
6.0

Thu
/
Fri

Fri
/
Sat

Sat
/
Sun

Sun
/
Mon

Mon
/
Tue

Tue
/
Wed

Wed
/
Thu

Habitual weekend sleep

Figure2. Mean and standard error of actigraphic sleep parameters before, during, and after the sleep
Figure 2. Mean and standard error (SE) of actigraphic sleep parameters before, during and after sleep intervention. Shared area indicates theintervention.
area* Significant
indicates
thefrom
periodof theat sleep
period of the Shaded
sleep intervention.
difference
control condition
P<0.05. intervention. * Significant difference fromcontrol condition at p<0.05.

Taylor et al (16). The study reported that a 2-hour delay
in wake-up time on the weekend deteriorated alertness
and performance until the middle of the next week. One
explanation for this discrepancy is that the participants inthe present study were habitually sleep deprived, whereas
normal sleepers (those who sleep approximately 8 hours)
participated in the previous study. Hence, the effects ofsleep extension might have worked to cancel potential
sleep debt that participants of the present study had been
accumulating. In the previous study (16), extended nighttime sleep (mean 9.8 hours) might act as “extra” sleep.
Sleep extension is shown to result in less clear improvements in alertness and performance for individuals without sleep debt (23, 25, 26). Another contributing factor

422

Scand J Work Environ Health 2011, vol 37, no 5

may be wake time. The participants in the present study
woke up by 09.00 hours at the latest (figure 2), whereas
those in Taylor et al’s study awoke at approximately 10:30
hours. Earlier wake time may prevent circadian phasedelay, causing negative influences on daytime function
on subsequent weekdays.
An important question in the present study is how
long the benefit of weekend sleep extension lasted following the subsequent Monday. It was unexpected thata significantly longer reaction time and a larger numberof lapses on the psychomotor vigilance task were foundon the Thursday after the intervention than after thehabitual weekend sleep condition (figure 3). This finding might be related to the immediate return of sleep

Kubo et al

300

Reaction time (ms)Lapse [>500ms] (number)

3.0

Mean± SE
N=26

*

280

Mean± SE
N=26

2.5

*

Condition: P=0.803
Day: P=0.606
Interaction: P=0.004

2.0
1.5

260
240

Condition: P=0.890
Day: P=0.745
Interaction: P=0.001

0

Mon

Thu

1.0

*

0.5

*

0.0
Mon

Thu

Mon

Sleep intervention

Thu

Mon

Thu

Habitual weekend sleep

Meanerrorand(SE)
standard
error ofvigilance
psychomotor
vigilance
for reaction
beforeFigure 3.Figure
Mean and3.standardof psychomotor
task for reaction
times task
and lapses
before andtimes
after theandsleeplapses
intervention.
Sharedarea indicatesperiodtheof thesleep
sleep intervention.
* Significant
difference
control condition
at P<0.05.
and theafterintervention.
Shadedarea fromindicates
the periodof the sleep intervention.

2.0

Drowsiness (score)
Mean± SE
N=26

1.8

2.0

1.6

1.4

1.4

Mon

Thu

Less

1.0

1.2

Condition: P=0.090
Day: P=0.006
Interaction: P=0.148
Mon

Thu

Sleep intervention

Eyestrain (score)
Mean± SE
N=26

1.8

1.6

1.2
Less

More

More

* Significant difference from control condition at p<0.05.

1.0

Condition: P=0.670
Day: P=0.001
Interaction: P=0.794
Mon

Thu

Mon

Thu

Habitual weekend sleep

Figure
4. Meanandsubjectiveforfatigue
questionnaire
for anddrowsinessandeyestrain
Figure 4. Meanand standard
error(SE)standardof subjectiveerror
fatigueofquestionnaire
drowsinessand eyestrain before
after the sleep
intervention.
Shared area
indicates
the after
period theof thesleep
sleep intervention.
beforeandintervention. Shaded area indicates the period of the sleep intervention.

Scand J Work Environ Health 2011, vol 37, no 5423

Weekend sleep extension for alertness and performance

130

Systolic blood pressure (mmHg)
Mean± SE
N=26

Condition: P=0.274
Day: P<0.001
Interaction: P=0.171

125

80

Diastolic blood pressure (mmHg)
Mean± SE
N=26

78
76

120
74
115

72

Condition: P=0.906
Day: P=0.071
Interaction: P=0.869

0

0
Mon

Thu

Mon

Thu

Sleep intervention

Mon

Thu

Mon

Thu

Habitual weekend sleep

Figure 5. Mean and standard error of blood pressure before and after the sleep intervention.

Figure 5.Shaded
Mean andarea
standard
error (SE)blood pressure
before andafter the sleep intervention. Shared area indicates the period of the sleep
indicates
theofperiodof the sleep
intervention.
intervention.

d­ uration following the intervention (from 7 to 5 hours).
In the present study, sleep duration on the weekends wasapproximately 2 hours longer per day for the intervention than the habitual weekend sleep condition (figure2). However, sleep duration on weekdays after the intervention returned to 5 hours. Thus, we assume that theimmediate return from the longer weekend sleep duration to the shorter weekday sleep duration may cause
impaired neurobehavioral performance in the intervention condition. Additionally, given that the cumulative
effects of mild sleep restriction became evident withina few days after the start of the restriction (23, 24, 27),
the favorable influences of sleep extension in this study
may be cancelled due to cumulative effects.
However, a recent study indicated that one weekof sleep extension not only improved performance andalertness during the subsequent period of sleep restriction but also facilitated recovery in the post-restriction
period (22). These findings were inconsistent with the
impairments of neurobehavioral performance on theThursday after the intervention. In the previous research,
the targeted participants were normal sleepers, but in thepresent research, short sleepers. Namely, the effects ofsleep extension in this study might work as compensation for accumulated sleep debt among short sleepers. In
contrast, one week of extended sleep times might resultin the benefits of sleep extension for normal sleepers.
When sleep duration is adequate not only on weekends
but also weekdays, the effects of sleep extension can be
maintained.

424

Scand J Work Environ Health 2011, vol 37, no 5

Furthermore, several possibilities exist regarding why
the impaired neurobehavioral performance occurred on
Thursday after the intervention. Responses to the intervention condition varied among the participants. In short,the standard deviation of reaction times and lapses was
2 or 3 times larger on Thursday after the intervention
than on Monday after the intervention (SD for Monday
and Thursday varied from 26.1–52.1 in reaction times
and 0.9–3.1 in lapses). Therefore, some of the workers
showed greater decreases in the performance of a reaction
time task toward Thursday, suggesting inter-individual
differences in response to a manipulated sleep–wakepattern (28, 29). On the contrary, the performance datain the habitual weekend sleep condition indicate that
deteriorated performance on the subsequent Monday was
restored to the baseline level on Thursday. Consequently,
the combined effects of these two factors are likely to leadto the current result of impaired neurobehavioral performance on Thursday after the intervention. Alternatively,
the workload intensity would be unexpectedly changed on
Thursday after the intervention. Another reason might bethat a type-1 error because the sample size in this study
was not large. Taken together, three days (Friday to Sunday) of sleep extension on weekends may have sustained
the benefits for only a few days following the intervention, as far as sufficient sleep duration on the subsequent
weekdays could be not ensured.
This study had some limitations. First, participantsin the present study slept <6 hours on weekdays, despite
the fact that they did not work extremely long hours

Kubo et al(about 80% of workers in this study had mean weekly
working hours of <50 hours). It is possible that they voluntarily curtailed their sleep duration. We interviewed
some of the participants about the causes of their habitually short sleep times, but no clear responses emerged. In
addition, the participating workers might be categorized
as individuals with behaviorally induced insufficient
sleep syndrome. Such a possibility, however, would bequite low, given the clinical presentation and the diagnostic criteria for this syndrome (30).
Second, it remains unclear whether the weekend
sleep extension had positive effects on work productivity because the participants’ work output was notevaluated.
Third, we did not measure how participants spent
their leisure time. Recently, a great deal of research has
been conducted on the importance of leisure activity
in fatigue recovery (31–33). Moreover, findings fromrecent studies indicate that increased control of working
time and/or days off plays a crucial role in improving
workers’ health (34). Therefore, the benefits of weekend
sleep extension are likely to vary depending on the typesof leisure activity in which the participants engage (eg,
active or passive leisure) and/or working style.
Fourth, the measurements in this study could havebeen more optimal through the selection of different parameters, such as a circadian phase marker (eg,melatonin). Besides, increased frequency of testing,rather than only on Monday and Thursday, might further
clarify the possible effects of the intervention. Furthermore, since sleep data in this study were measured by
actigraphy instead of polysomnography, sleep might
have been overestimated (35). Thus, it is possible thatsleep extension on weekends was <2 hours per day.
Fifth, the present study did not address the long-term
effects of sleep extension on weekends, and it remains
unclear what they would be. But we speculate that theweekend sleep extension may yield favorable effects
only on a few days of the following week because
sleep duration on weekdays would be short, even if theintervention were repeated for a long period. Both organizational and individual efforts should thus be directed
to ensuring sufficient duration of sleep not only on theweekends but also on weekdays.
Finally, it may be difficult to continue the weekend
sleep intervention over a long period, given the present
data showing an immediate return to short sleep following the weekends. We believe that the participants’ highcompliance was achieved because of the single shortterm (2–3 days) intervention that spanned a weekend.
The sleep intervention in this study succeeded inlengthening the sleep duration of workers with habitually short sleep periods. Longer weekend sleep resulted
in acute improvements of alertness and performance,
but the improvements were not present later during theworkweek. However, the benefits of weekend sleep
extension might be maintained if the participants receive
sufficient sleep during the post-intervention week. Ourpresent findings suggest the significance of vouchsafing adequate sleep nightly for optimal levels of worker
safety and health.

Acknowledgement
The study was supported by a Grant-in-Aid from the
National Institute of Occupational Safety and Health,Japan (P18-01, P22-01).

References1OECD. Employment outlook [Internet]. Paris: OECD. 2008.
[Cited 28 July 2010.] Available from: http://wwwoecdorg/
dataoecd/54/57/40846335.pdf.

2Åkerstedt T, Fredlund P, Gillberg M, Jansson B. Work load
and work hours in relation to disturbed sleep and fatigue in alarge representative sample. J Psychosom Res. 2002;53:585–8.
doi:10.1016/S0022-3999(02)00447-6.

3

Iwasaki K, Takahashi M, Nakata A. Health problems due
to long working hours in Japan: working hours, workers’
compensation (Karoshi), and preventive measures. Ind Health.
2006;44:537–40. doi:10.2486/indhealth.44.537.

4

Kleppa E, Sanne B, Tell GS. Working overtime is associatedwith anxiety and depression: the Hordaland Health Study.
J Occup Environ Med. 2008;50:658–66. doi:10.1097/
JOM.0b013e3181734330.

5

Nakashima M, Morikawa Y, Sakurai M, Nakamura K, Miura
K, Ishizaki M, et al. Association between long working hours
and sleep problems in white-collar workers. J Sleep Res. 2011
Mar;20(1):110–6. doi:10.1111/j.1365-2869.2010.00852.x.

6

Suwazono Y, Nagashima S, Okubo Y, Uetani M, Kobayashi
E, Kido T, et al. Estimation of the number of working
hours critical for the development of mental and physicalfatigue symptoms in Japanese male workers – application ofbenchmark dose method. Am J Ind Med. 2007;50:173–82.
doi:10.1002/ajim.20432.

7

Japan Ministry of Internal Affairs and Communications.
Summary of results of the 2006 survey on time use andleisure activities [Internet]. Tokyo: Japan Ministry of Internal
Affairs and Communications;2006. [Cited 13 October2010.] Available from: http://www.stat.go.jp/english/data/shakai/2006/pdf/jikan-a.pdf.

8Åkerstedt T, Nilsson PM, Kecklund G. Sleep and recovery.
In: Sonnentag S, Perrewe PL, Ganster DC, editors. Current
perspectives on job-stress recovery. Bingley, UK: JAI Press;2009. p205–47.

9Dahlgren A, Kecklund G, Åkerstedt T. Overtime work andScand J Work Environ Health 2011, vol 37, no 5

425

Weekend sleep extension for alertness and performanceits effects on sleep, sleepiness, cortisol and blood pressure inan experimental field study. Scand J Work Environ Health.
2006;32:318–27.
10 Härmä M. Work hours in relation to work stress, recovery
and health [review]. Scand J Work Environ Health.
2006;32:502–14.
11 Tucker P, Brown M, Dahlgren A, Davies G, Ebden P, Folkard
S, et al. The impact of junior doctors’ worktime arrangementson their fatigue and well-being. Scand J Work Environ Health.
2010;36:458–65. doi:10.5271/sjweh.2985.
12 Beckers DG, van Hooff ML, van der Linden D, Kompier MA,
Taris TW, Geurts SA. A diary study to open up the black box
of overtime work among university faculty members. Scand J
Work Environ Health. 2008;34:213–23.
13 van der Hulst M. Long work hours and health [review]. Scand
J Work Environ Health. 2003;29:171–88.

24 Axelsson J, Kecklund G, Åkerstedt T, Donofrio P, Lekander
M, Ingre M. Sleepiness and performance in response torepeated sleep restriction and subsequent recovery duringsemi-laboratory conditions. Chronobiol Int. 2008;25:297–308.
doi:10.1080/07420520802107031.
25 Harrison Y, Horne JA. Long-term extension to sleep – arewe really chronically sleep deprived? Psychophysiology
1996;33:22–30. doi:10.1111/j.1469-8986.1996.tb02105.x.
26 Horne J, Anderson C, Platten C. Sleep extension versus nap
or coffee, within the context of ‘sleep debt.’ J Sleep Res.
2008;17:432–6. doi:10.1111/j.1365-2869.2008.00680.x.
27 Van Dongen HP, Maislin G, Mullington JM, Dinges DF. The
cumulative cost of additional wakefulness: dose-response
effects on neurobehavioral functions and sleep physiology
from chronic sleep restriction and total sleep deprivation.
Sleep. 2003;26:117–26.

14 Virtanen M, Ferrie JE, Gimeno D, Vahtera J, Elovainio
M, Singh-Manoux A, et al. Long working hours and sleep
disturbances: the Whitehall II prospective cohort study. Sleep.
2009;32:737–45.

28 Van Dongen HP, Baynard MD, Maislin G, Dinges DF.
Systematic interindividual differences in neurobehavioral
impairment from sleep loss: evidence of trait-like differential
vulnerability. Sleep. 2004;27:423–33.

15 Virtanen M, Singh-Manoux A, Ferrie JE, Gimeno D,
Marmot MG, Elovainio M, et al. Long working hours andcognitive function: the Whitehall II Study. Am J Epidemiol.
2009;169:596–605. doi:10.1093/aje/kwn382.

29 Kubo T, Takahashi M, Tachi N, Takeyama H, Ebara T, Inoue
T, et al. Characterizing recovery of sleep after four successivenight shifts. Ind Health. 2009;47:527–32. doi:10.2486/
indhealth.47.527.

16 Taylor A, Wright H, Lack L. Sleeping-in on the weekend
delays circadian phase and increases sleepiness the following
week. Sleep and Biological Rhythms. 2008;6:172–9.
doi:10.1111/j.1479-8425.2008.00356.x.

30 American Academy of Sleep Medicine. Behaviorally induced
insufficient sleep syndrome. In: International classificationof sleep disorders. Diagnostic and coding manual, 2nd ed.
Westchester, IL: American Academy of Sleep Medicine; 2005.
p104–6.

17 Yang CM, Spielman AJ, D’Ambrosio P, Serizawa S, Nunes
J, Birnbaum J. A single dose of melatonin prevents the phasedelay associated with a delayed weekend sleep pattern. Sleep.
2001;24:272–81.

31 Sonnentag S, Jelden S. Job stressors and the pursuit of sport
activities: A day-level perspective. J Occup Health Psychol.
2009;14:165–81. doi:10.1037/a0014953.

18 Horne JA, Östberg O. A self-assessment questionnaire to
determine morningness-eveningness in human circadianrhythms. Int J Chronobiol. 1976;4:97–110.

32 Tucker P, Dahlgren A, Akerstedt T, Waterhouse J. The impactof free-time activities on sleep, recovery, and well-being. Appl
Ergon. 2008;39:653–62. doi:10.1016/j.apergo.2007.12.002.

19 Dinges D, Powell J. Microcomputer analyses of performanceon a portable simple visual RT task during sustained
operations. Behavior research methods, instruments, &computers. 1985;17:652–5. doi:10.3758/BF03200977.

33 Winwood P, Bakker A, Winefield A. An investigation of therole of non-work-time behavior in buffering the effects ofwork strain. J Occup Environ Med. 2007;49:862. doi:10.1097/
JOM.0b013e318124a8dc.

20 Kubo T, Tachi N, Takeyama H, Ebara T, Inoue T, Takanishi
T, et al. Characteristic patterns of fatigue feelings on four
simulated consecutive night shifts by “Jikaku-sho shirabe.”
Sangyo Eiseigaku Zasshi. 2008;50:133–44.

34 Takahashi M, Iwasaki K, Sasaki T, Kubo T, Mori I, Otsuka
Y. Worktime control-dependent reductions in fatigue, sleep
problems, and depression. Appl Ergon. 2011;42:244–50.
doi:10.1016/j.apergo.2010.06.006.

21 Cole RJ, Kripke DF, Gruen W, Mullaney DJ, Gillin JC.
Automatic sleep/wake identification from wrist activity. Sleep
1992;15:461–69.

35 Ancoli-Israel S, Cole R, Alessi C, Chambers M, Moorcroft
W, Pollak CP. The role of actigraphy in the study of sleep andcircadian rhythms. Sleep. 2003;26:342–92.

22 Rupp TL, Wesensten NJ, Bliese PD, Balkin TJ. Banking sleep:
realization of benefits during subsequent sleep restriction andrecovery. Sleep. 2009;32:311–21.
23 Belenky G, Wesensten NJ, Thorne DR, Thomas ML, Sing HC,
Redmond DP, et al. Patterns of performance degradation andrestoration during sleep restriction and subsequent recovery:a sleep dose-response study. J Sleep Res. 2003;12:1–12.
doi:10.1046/j.1365-2869.2003.00337.x.

426

Scand J Work Environ Health 2011, vol 37, no 5

Received for publication: 15 October 2010