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Vol.1, No.4, 284-289 (2009)
doi:10.4236/health.2009.14046
SciRes
Copyright © 2009 Openly accessible at http://www.scirp.org/journal/HEALTH/
Health
The effects of lunch time napping on habitual nappers’
mental work efficiency in the afternoon and early
evening: an empirical study from China
Guang-Jin Zhang1, Fei-Fei Sun2, Jian-Qiao Liao3
1Politics and Law School, China University of Geosciences, Wuhan, China; hbzgj@126.com
2Faculty of Foreign Languages, Jiangxi University of Finance and Economics, Nanchang, China
3Management School, Huazhong University of Science and Technology, Wuhan, China
Received 27 September 2009; revised 5 November 2009; accepted 11.November 2009.
ABSTRACT
30 college students who have the habit of lunch
time napping (LTN) participated in experiments
under two different conditions: Having lunch
time napping and not having lunch time napping.
They were asked to complete three tasks in-
cluding vigilance reaction, short-term memory,
addition arithmetic; their performance was re-
corded automatically by computer during 3 dif-
ferent periods in the afternoon and early eve-
ning. The analysis about the experimental data
showed that: as for habitual nappers, midafter-
noon nap zone existed, LTN played a very im-
portant role in overcoming it, and did great help
in enhancing their vigilance in the afternoon and
early evening, however, LTN didn’t bring sig-
nificant positive effect to executing complex
tasks (such as short-term memory and addition
task) at the periods of time 16:30-17:30, 20:00-
21:00. Finally, this article discussed the conclu-
sions and its significance.
Keywords: Lunch Time Napping; Mental Work
Efficiency
1. INTRODUCTION
Lunch time napping is very prevalent in China. The
farmers often take LTN only in summer because they
need avoid the hot sun’s radiation at noon; however,
more and more mental workers also take LTN, moreover,
they usually take LTN all the year round, which can’t be
explained by the weather. An investigation in a univer-
sity found that 71% teachers and 78% students are used
to taking LTN more than 10 months a year; the respon-
dents admitted that they won’t perform well or work
efficiently in the afternoon and evening without LTN.
However, LTN also induced a lot of controversies, some
people think that it leads to low work efficiency for that
the continuity of eight hours work a day is interrupted by
LTN. Besides, LTN extends the time between going to
work and getting off work, especially for those whose
home is far away from work site, such as the work time
of not having HTL is often from 9:00 to 17:00, otherwise,
it is usually from 8:00 to 17:30, which makes people feel
more tired [1]. Dose not having LTN really lead to ha-
bitual nappers’ mental work inefficiency?
To look for the answer from former researches, there
were two difficulties. Firstly, Chinese literature usually
only describes people’s subjective feeling, few of them
studies the effects of LTN based on the actual work per-
formance. Secondly, in most of relative English litera-
ture, the napping time is often in the afternoon or in the
evening, even in a few of researches about LTN, the du-
ration of napping is very short, which is not consistent
with the situation of China. For example, Macchi, Bou-
los and Ranney et al. studied the effects of afternoon nap
on nighttime alertness and performance [2]. McEvoy &
Lack studied the effects of nap (happens in the night
shift) on work efficiency [3]. Mednick, Nakayama and
Cantero et al. studied the restorative effects of afternoon
naps on perceptual deterioration [4]. Backhaus & Jung-
hanns studied effects of afternoon nap on memory ability
[5]. Milner, Fogel and Cote studied the effects of after-
noon nap on motor performance and the moderation ef-
fects of habitual napping between them [6]. Hayashi et
al. studied the effects of both afternoon nap and lunch
time nap on mood, performance and EEG activity [7-8].
Driskell and Mullen made A Meta-Analysis about the
efficacy of naps as a fatigue countermeasure [9]. Almost
all the naps studied mentioned above in the afternoon,
which is the working time in China, the working time in
the afternoon in China is often from 14:00 to 17:30 or
14:30-18:00. LTN is a common phenomenon in China,
and the napping duration is usually as long as 1 hour to
1.5 hours (12:30-13:30 or 12:30-14:00). Therefore, the
context about the western scholars’ researches is far dif-
ferent from Chinese reality, the conclusions of those
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researches can’t be simply applied to practice in China.
For the two pieces of reasons above, this research is to
study the effects of LTN on habitual ‘nappers’ mental
work efficiency in the afternoon and early evening
through experiment.
2. METHOD
2.1. Subjects
30 college students (18 females and 12 males) partici-
pated in the experiment. These subjects have the habit of
lunch time napping, they have lunch time napping at
least 4 times a week, and more than thirty minutes each
time, their night sleep is often from 23:00 to 7: 00, they
are healthy and don’t have the habits of smoking and
heavy drinking. They did not take any drug during the
experiment; meanwhile, all subjects are voluntary and
given payment.
2.2. Procedure
The experiment is a balance intra-group design, that is,
the 30 subjects were simple randomly divided into two
groups with the same number. Each group participated
once in two kinds of condition experiment（Having LTN
and not having LTN), in order to eliminate the possible
influence of the shift experimental condition on work
efficiency in the next day, the two tests under different
experimental condition which each group subjects par-
ticipated in were conducted at one week interval. In par-
ticular, half of the subjects firstly participated in the ex-
periment under the condition of having LTN, and then
took the second test under condition of not having LTN
one week later; the other half took the first test under not
having LTN condition, and then took the second test
under having LTN condition after a week.
In this study, the two kinds of experimental conditions
are having LTN and not having LTN. The former is to let
the subject have lunch time napping in dormitory from
12:30 to 14: 00, and arrive at the lab at 14:25. The later
is to let the subjects arrive at the lab by 12:30, and they
can do anything except taking naps until 14:25. In the
week before the first experiment test and the week in-
terval between the two experiment tests, the subjects
were required to take normal night sleep and lunch time
napping everyday, and to keep daily log so as to be
checked. In order to let the subjects be familiar with and
proficient at the experimental tasks, in the morning of
the day before the first experiment test, all subjects par-
ticipated in the instructions of the experiment and took
15 minutes practice for the three experimental tasks.
Each experiment includes three periods. The first pe-
riod lasts from 14:30 to 15:30, the second period lasts
from 16:30 to 17:30, and the third period is from 20:00
to 21:00. During the experiment, the subjects were not
allowed to leave the laboratory except for having supper
outside, they can read novel, play games or chat in the
laboratory between the three periods. The reason for the
first period design is that most organizations in China
require their employees to start work at 14:30 in summer;
the second period and the third period are to measure the
effects of LTN on work efficiency before off duty in the
afternoon and in the early evening.
In each period of the experiment, all subjects need
accomplish three tasks: vigilance reaction, short-term
memory, addition arithmetic, after each task there will be
five-minute rest. As for the task of vigilance reaction, it
needs the subjects response to 40 signals; as for the task
of short-term memory, it needs the subjects recall 20
groups of English letters; as for the task of addition, it
needs the subjects judge whether right or not about 30
equations of pairs of three-digit number addition. It will
take about one hour to finish all the three tasks.
In order to motivate the subjects to participate in the
experiment seriously, we had clarified that better per-
formance and more payment.
2.3 Experimental Task
This study chose three typical mental workers as the
experimental tasks.
One of the experimental tasks is vigilance reaction.
This experimental task is completed on the computer.
There is a clock designed by the researcher on computer
screen, and the clock is the same as the one in our daily
life. There is only one exception that its second hand
occasionally walked 2 grids, and the requirement for
subjects is to press the “Del” button in low right corner
of the keyboard when the second hand walked 2 grids,
then the computer would automatically record the sub-
ject’s response. During the experimental task, the prob-
ability of second hand randomly walked 2 grids was 0.02,
in other words, the second hand walked 2 grids once
about on the average of 50 seconds, the probability is
very appropriate, for if it is too small, signals appeared
little, it would make subjects divert attention easily; if it
is too large, signals appeared much, this would lead to
the loss of the vigilance reaction characteristic. Since the
second hand walked 2 grids is a random event, so within
30 minutes on each subject’s computer screen, the num-
ber of signals was different, therefore, and the rate of
wrong response was to evaluate the level of vigilance for
the subjects. Here, the rate of wrong response refers to
the total number which is the number of the second hand
walked 2 grids but the subject didn’t press the “Del”
button adds the number of the second hand walked nor-
mally but the subject pressed “Del” button in the propor-
tion of the total number of the second hand walked 2
grids.
The second experimental task is short-term memory.
The earlier research has shown that human short-term
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286
memory capacity is very limited and its storage time is
short, it was considered as the bottleneck of human in-
formation procession. In this task, 20 groups of alphabet
need the subjects recall one by one, and every group of
alphabet consist of 10 letters, 10 letters showed on the
computer screen in succession at a speed of one letter
every two seconds, when the last letter of one group al-
phabet appeared, there were 10 seconds for the subjects
to write the letters just showed on the computer screen
from their memory, the computer will automatically
compare the letters which the subjects wrote down with
the alphabet, the number of the letters recalled correctly
will be taken as the subjects’ short-term memory per-
formance, and the average number of the 20 groups of
letters recalled correctly will be taken as the data to be
analyzed in the following.
The third experimental task is addition arithmetic. The
computer will display an equation of a pair of three-digit
numbers addition on the screen every time, such equa-
tions in total up to 30, some of them are wrong, and
some are right. The task required the subjects to judge
them whether right or not as quickly and accurately as
possible. Pressing the button “enter” on the low right
keyboard when the equation is right, and pressing the
button “ctrl” on the low left keyboard when the equation
is wrong, the next equation appeared immediately when
the subjects completed pressing key, the computer will
automatically record the judging time and check whether
the judge is right or not, the average judging time and
the correct judging rate for the 30 equations will be ana-
lyzed.
3. RESULTS
3.1. Vigilance Reaction Analysis
The vigilance reaction performance under two kinds of
experimental condition in each period was analyzed by
paired-samples T test, in addition, the vigilance reaction
performance under the same experimental condition in
three periods was analyzed with ANOVA, and the result
is shown in Ta b l e 1. The same analysis to short-term
memory, addition arithmetic, and results are shown in
Ta b l e 2 , Ta b le 3, and Ta bl e 4 .
Ta b l e 1 shows that in three experimental periods, the
subjects who took LTN have significantly higher vigi-
lance than those without LTN, such situation especially
obvious at 14:30-15:30, the napping subjects’ rate of
signals responded wrong is 10% lower than that of not
napping ones, even at 16:30-17:30 and 20:00-21:00, the
rate of signals responded wrong is also 4% lower, which
proves that lunch time napping exert positive effect on
vigilance for people no matter in the afternoon or in the
early evening.
Ta b l e 1 also shows that for the LTN subjects, their
vigilance hadn’t changed significantly in the three ex-
perimental periods; however, as for the not having LTN
subjects, their vigilance at 14:30-15:30 is significantly
lower than that at 16:30-17:30 and 20:00-21:00, there
wasn’t significant difference between the second period
and third period.
3.2. Short-term Memory Analysis
Ta b l e 2 lists the comparative analysis results of subjects’
short-term memory capacity under two experimental
conditions and in three experimental periods.
It can be seen from Tab l e 2 that only at 14:30-15:30,
the subjects who took LTN have better short-term mem-
ory performance than those without LTN, at 16:30-17:30
and 20:00-21:00, there wasn’t significant difference be-
tween them.
Ta b l e 2 shows that, as for the subjects who took LTN,
the significant difference about short-term memory ca-
pacity wasn’t found in three periods, however, as for the
subjects who didn’t take LTN, their short-term memory
performance at 14:30-15:30 is worse than that at
16:30-17:30 and 20:00-21:00, and there wasn’t signifi-
cant difference between 16:30-17:30 and 20:00-21:00.
3.3. Addition Arithmetic Analysis
In order to analyze the effect of LTN on human arithme-
tic calculation performance, this research made the
comparative analysis of calculation speed and calcula-
tion accuracy rate under two different experimental con-
ditions and in three experimental periods, the results
shown in Ta b l e 3 and Tab l e 4 .
Ta b l e 3 lists the comparative analysis results of
arithmetic calculation speed under two experimental
conditions and in three experimental periods.
Ta b l e 3 shows that only at 14:30-15:30, the arithmetic
calculation speed of the subjects who took LTN is sig-
nificantly faster than that of those without LTN, while at
16:30-17:30 and 20:00-21:00, the significant difference
wasn’t found between them.
As can be seen from Tab l e 3 , for the subjects who
took LTN, their arithmetic calculation speed is almost
the same, but for the subjects who didn’t take LTN, the
arithmetic calculation speed at 14:30-15:30 is signifi-
cantly slower than that at 16:30-17:30 and 20:00-21:00,
and there wasn’t significant difference between
16:30-17:30 and 20:00-21:00.
Ta b l e 4 lists the comparative analysis results of the
calculation accuracy rate under two experimental condi-
tions and in three experimental periods.
Ta b l e 4 shows that only at 14:30-15:30, the calcula-
tion accuracy rate of subjects who took LTN is signifi-
cantly higher than that of those without LTN, while at
16:30-17:30 and 20:00-21:00, the significant difference
couldn’t be found between them.
As can be seen from Tab l e 4, as for the subjects who
took LTN, their arithmetic calculation accuracy rate is
almost the same, but for the subjects who didn’t take LTN,
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287
Ta b l e 1 . Vigilance reaction (the rate of signal responded wrong).
experimental periods
Experimental
condition
the rate of
signal re-
sponded
wrong
14:30-15:30 16:30-17:30 20:00-21:00 F LSD
Mean 0.054
(NVR1)
0.063
(NVR2)
0.060
(NVR3)
Having lunch
time napping Std.dev. 0.044 0.043 0.045
0.309
NVR1≈NVR2
NVR1≈NVR3
NVR2≈NVR3
Mean 0.148
(NNVR1)
0.105
(NNVR2)
0.102
(NNVR3)
Not Having
lunch time nap-
ping Std.dev. 0.060 0.055 0.058
5.948**
NNVR1> NNVR2
NNVR1> NNVR3
NNVR2≈NNVR3
T 20.828** 10.779** 9.069**
Ta b l e 2 . Short-term memory capacity (the number of letters recalled correctly).
experimental periods
Experimental
condition
Short-term
memory
capacity 14:30-15:30 16:30-17:30 20:00-21:00 F LSD
Mean 8.05
(NSM1)
8.09
(NSM2)
8.01
(NSM3)
Having lunch
time napping Std.dev. 0.340 0.373 0.412
0.383
NSM1≈NSM2
NSM1≈NSM 3
NSM2≈NSM 3
Mean 7.30
(NNSM1)
7.96
(NNSM2)
7.92
(NNSM3)
Not Having
lunch time nap-
ping Std.dev. 0.390 0.582 0.334
20.588**
NNSM1< NNSM2
NNSM1< NNSM3
NNSM2≈NNSM3
T 31.068** 1.145 1.665
Table 3. Arithmetic calculation speed (seconds/one equation).
experimental periods Experimental
condition
arithmetic
calculation
speed 14:30-15:30 16:30-17:30 20:00-21:00 F LSD
Mean 5.06
(NCS1)
5.03
(NCS2)
4.99
(NCS3)
Having lunch
time napping
Std.dev. 0.339 0.338 0.402
0.322
NCS1≈NCS2
NCS1≈NCS3
NCS2≈NCS3
MeNot Having
lunch time nap-
ping
an 5.49
(NNCS1)
5.01
(NNCS2)
5.04
(NNCS3)
Std.dev. 0.402 0.405 0.337
14.980**
NNCS1< NNCS2
NNCS1< NNCS3
NNCS2≈NNCS3
T 15.086** 0.813 1.708
Ta b l e 4 . The calculation accuracy rate.
experimental periods
Experimental
condition
the calcula-
tion accuracy
rate 14:30-15:30 16:30-17:30 20:00-21:00 F LSD
Mean 0.763
(NCAR1)
0.762
(NCAR2)
0.766
(NCAR3)
Having lunch
time napping Std.dev. 0.041 0.042 0.040
0.058
NCAR1≈NCAR2
NCAR1≈NCAR3
NCAR2≈NCAR3
Mean 0.701
(NNCAR1)
0.756
(NNCAR2)
0.752
(NNCAR3)
Not Having
lunch time nap-
ping Std.dev. 0.763 0.072 0.075
5.272**
NNCAR1< NNCAR2
NNCAR1< NNCAR3
NNCAR2≈NNCAR3
T 7.423** 0.670 1.391
the arithmetic calculation accuracy rate at 14:30-15:30
is significantly lower than that at 16:30-17:30 and
20:00-21:00, and there wasn’t significant difference be-
tween 16:30-17:30 and 20:00-21:00.
4. DISCUSSION
4.1. Conclusions
This research showed that as for the subjects who didn’t
take LTN, their mental work performance at 14:30-15:30
is significantly worse than that at 16:30-17:30 and
20:00-21:00, while as for those who took LTN, their
mental work performance almost is the same in three
experimental periods, which indicated that midafternoon
nap zone as Hayashi et al. [10], Broughton mentioned
exists objectively for habitual nappers [11], this experi-
ment provided the direct evidence for their standpoint.
This research also showed that the subjects who took
LTN have significantly better mental work performance
than those without LTN at 14:30-15:30, which proved
that LTN could overcome habitual nappers’ “midafter-
noon nap zone”.
It is interesting that as for mental work performance
of such task as short-term memory and arithmetic calcu-
lation, there wasn’t significant difference between the
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subjects who took LTN and those who didn’t take it at
16:30-17:30 and 20:00-21:00, however, as for vigilance
reaction, the subjects who took LTN have significantly
better performance than those who didn’t take it at the
periods as above, which may be caused by the different
nature of the experimental tasks. In specification, the
experimental task of vigilance reaction is relatively bald,
such tasks may easily induce the subjects who didn’t
take LTN to desire sleep, and the result is that their per-
formance is worse than the subjects who took LTN. Ha-
yashi et al. also took for that nap could reduce human
sleepiness and enhance vigilance [7,8,12]. However, as
for short-term memory and arithmetic calculation, these
tasks’ mental workload are relatively overload, the sub-
jects who didn’t take LTN weren’t easily to stimulate
sleepiness, and the result is that their performance are
the same as those who took LTN. Hayashi et al. have
also gotten such conclusion [7]. This research results
indicated that the effect of LTN on habitual nappers’
mental work performance is moderated by the nature of
mental work at 16:30-17:30 and 20:00-21:00.
It is worth noting that this research didn’t deny the
existence of sleep inertia. Hayashi et al. hold that sleep
inertia is inevitable [7], and Taub [13], Dinges et al. be-
lieved that sleep inertia may last 15-35 minutes [14]. In
this study, the measurement of mental work performance
is carried out 30 minutes after LTN, as for the subjects
who took LTN, their mental work performance has not
changed significantly, which provides indirect evidence
for that sleep inertia may last 15-35 minutes, because if
sleep inertial exceeds 30 minutes, the mental work per-
formance of the subjects who took LTN at 14:30-15:30
should be lower than that at 16:30-17:30 and 20:00-21:00,
but this experiment result wasn’t the case.
It should be noted that the above conclusions are got
with the subjects who have LTN habit and took normal
sleep at night and 1 hour and a half naps at noon, if ex-
perimental context was not the case, the conclusion of
this study may be different, many scholars believed that
the effects of naps depend on the duration of prior wake-
fulness, the time of day of the nap, and its duration
[15,16].
Many people feel that they are sleepy and work ineffi-
ciently in the afternoon and evening without LTN; how-
ever as for the complex and over-workload task, such as
short-term memory and arithmetic calculation, the con-
clusion of this study is contradict with it, it doesn’t mat-
ter whether to take LTN or not, human work perform-
ance of such complex task at 16:30-17:30 and 20:00-21:00
is the same, the reason may due to the difference be-
tween experiment and reality. In the experiment, sub-
jects’ attention is highly focused, the pace of task is rela-
tively fast, the experiment duration is short (each period
about 1 hour), and also strong incentive provided. In
reality, the pace of many tasks is slow, and the work du-
ration is long, which easily induce people to be relaxed
and stimulate sleepiness. Despite some difference be-
tween experimental context and reality, we think that
this experiment proved that at least in theory, for com-
plex and over-workload mental work, LTN is a phe-
nomenon to be overcome temporarily in the later after-
noon and in the early evening (16:30-17:30 and
20:00-21:00), not having LTN didn’t exert significant
negative effect to the performance of such task.
4.2. Recommendations
As for habitual nappers, because of LTN can ease such
physical embarrassment as mid-afternoon nap zone,
therefore, LTN is needed if conditions allow, especially
for those whose home is near to their work site. For the
task of vigilance reaction, LTN is particularly important
because LTN can improve its performance in the after-
noon and evening.
Whether having LTN or not has great influence on
habitual nappers’ mental work efficiency at 14:30-15:30
in order to eliminate the negative influence, on one
hand, the government departments should try to avoid
arranging important mental activities at this period of
time, such as examinations, and so on. Unfortunately,
Chinese government departments doesn’t seem to no-
tice it, for example, the most important college en-
trance examination, its examination time in the after-
noon was always from 14:00 to17:00, as for some
students who did not take LTN, their test score are
likely to be lower than their real achievements, which
is unfair for them to compete with students who have
comfort LTN condition. On the other hand, many
Chinese enterprises should adjust their shiftwork
schedule, that is changing the present shiftwork time-
table (8:00-16:00, 16:00-24:00, 24:00 -8:00) into the
new one (6:00-14:00, 14:00-22:00, 22;00-6:00), which
can let habitual nappers avoid not had HLT on duty
yet at 14:30-15:30.
4.3. Limitations and Future Directions
All the subjects participated in this experiment have
LTN habit, although it consists of the Chinese work and
rest mode, we can’t find out the effect of LTN on mental
work efficiency of those who haven’t LTN habit, there is
no doubt that to study it is an interesting work, for ex-
ample, if we find that LTN has no significant effect on
mental work efficiency of those who haven’t LTN habit,
in addition, changing the LTN habit doesn’t bring sig-
nificant bad physical influence, then to reform Chinese
public sectors’ work and rest timetable is go without
saying, because the timetable (9:00 -17:00) in many pri-
vate sector is more reasonable than the timetable (8:00
-12:00 and 14:00-17:30) in public sectors obviously,
which keeps the continuity of eight hours work a day
and not require the public to wait out of the government
G. J. Zhang et al. / HEALTH 1 (2009) 284-289
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5. ACKNOWLEDGMENT
[9] Driskell, J.E. and Mullen, B. (2005) The efficacy of naps
as a fatigue countermeasure: a meta-analytic integration.
Human Factors., 2, 360-377.
This study was supported by the Science and Technology Research
Project of Hubei province under Grant B20080402, and also was sup-
ported by the Humanity Social Science Foundation of Hubei province
under Grant 2008y054. [10] Hayashi, M., Morikawa, T. and Hori, T. (2002) Cir-
casemidian 12-hour cycle of slow wave sleep under con-
stant darkness. Clinical Neurophysiology., 113 ,
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