The Quantitative Effects of Mattress and Sleep Postures on Sleep Quality

Abstract

Mattress, as a sleep platform, its types and physical properties have important effects on sleep quality and rest efficiency. In this paper, by subjective evaluations, analysis of sleeping behaviors, the relationship between the sleep postures, change postures and sleep quality were studied. The results showed that: (1) the mattress properties had a remarkable effect on sleep behaviors and sleep quality; (2) Sleep behaviors had a close relationship with sleeping postures and sleep habits. The characteristics of sleep behaviors vary from person to person; (3) Chinese people had tended to prefer supine posture, and the number of turns during night was less in supine position than in the lateral position.

Full text

Chapter 11
The Quantitative Effects of Mattress
and Sleep Postures on Sleep Quality
Yu-xia Chen, Yong Guo, Li-ming Shen and Sheng-quan Liu
Abstract Mattress, as a sleep platform, its types and physical properties have
important effects on sleep quality and rest efficiency. In this paper, by subjective
evaluations, analysis of sleeping behaviors, the relationship between the sleep
postures, change postures and sleep quality were studied. The results showed that:
(1) the mattress properties had a remarkable effect on sleep behaviors and sleep
quality; (2) Sleep behaviors had a close relationship with sleeping postures and
sleep habits. The characteristics of sleep behaviors vary from person to person;
(3) Chinese people had tended to prefer supine posture, and the number of turns
during night was less in supine position than in the lateral position.
Keywords Mattress Sleep movements Sleep postures Sleep quality
11.1 Introduction
Although the use of western-style mattress has been accepted by more and more
Chinese people, there exist few intensive studies on mattress properties and Chi-
nese demands. Compared with traditional beds, western-style mattresses seem to
This work was supported by a grant from the National Natural Science Foundation of China
(No. 31070503/C160302).
Y. Chen (&)Y. Guo S. Liu
College of Forest and Garden, Anhui Agricultural University,
Hefei 230036, People’s Republic of China
e-mail: sheherose@163.com
L. Shen
College of Furniture and Industrial Design, Nanjing Forest University,
Nanjing 210037, People’s Republic of China
E. Qi et al. (eds.), International Asia Conference on Industrial Engineering
and Management Innovation (IEMI2012) Proceedings,
DOI: 10.1007/978-3-642-38445-5_11, ÓSpringer-Verlag Berlin Heidelberg 2013
107

have brought more sleep disturbances and health problems. A survey of the US
public concerning the quality of sleep has showed that 7 % of the subjects indi-
cated that their sleeping problems were related to an uncomfortable mattress
(Addison et al. 1986). Among them incorrect sleeping postures and insufficient
support conditions, especially insufficient support of the low back was one of the
most important factors causing low-back pain (Hildebrandt 1995). Park et al. have
reported that the comfort of a bed was more heavily influenced by secondary
properties, such as spinal curvature and distribution of body pressure in Human-
Bed system than the primary properties of the material of mattress itself. However,
these studies have not provided evidence that sleep quality differs according to
mattress properties (Lee and Park 2006).
Lee and Park (2006) studied the effects of ‘‘comfortable’’ and ‘‘uncomfortable’’
mattress, although they did not find differences in sleep architecture, their
experimental results showed that ‘‘comfortable’’ mattresses could help to reduce
the movements in the stage of deep sleep (Lee and Park 2006). In fact, sleep is a
complex phenomenon; sleep quality is affected by a combined action of physio-
logical factors psychological factors and external environments.
The objective of this study was to investigate the Chinese people’s demands on
mattress and the relationship between the sleep postures, mattresses and sleep
quality.
11.2 Methodology
Each subject was recorded at least 4 consecutive nights (starting on Monday night
and ending on Friday morning) on each of the 18 mattresses. The subjects were
blind to the bedding materials and structure of spring mattress. Two weeks prior
(Jacobson et al. 2008) to the test all participants were asked to sleep in the sleep
laboratory to adapt the laboratory conditions and maintain a constant life style
without change in sleeping habits. The temperature and relative humidity in the
sleep laboratory was controlled at 25 ±1°C and 50 ±5 %, respectively.
To minimize the seasonal influence on sleep quality (Kleitman 1939), the test took
place from September to December.
(1) Subjects: The subjects, participating voluntarily in the study, had good
health, simple life style, regular sleep habits, no history or symptoms of sleep
disorders, and were not heavy snorers. The participants were required to sleep still
on the experimental mattress during each testing cycle. No medicine, tea, coffee,
and other stimulating beverages were allowed 3 h prior to the sleeping test.
Volunteers were 11 female graduate students, age of 20–32 years. Average height,
weight, and body mass index were 159.81 cm (±9.88 cm), weight 51 kg
(±6.5 kg), and 20.2 (±3.3), respectively.
(2) Body movements during sleep: Subject body movements were recorded in
the dark using Ingra-red video cameras and meanwhile observed by the technicians
outside of the sleeping room through monitors.
108 Y. Chen et al.

(3) Sleep diaries and visual analogue Scales (VAS): A self-report of sleep was
measured with a sleep diary that was filled out each morning immediately upon
arising. The subjects needed to answer questions about any external disturbance
during the night, the subjective quality of sleep, the level of fatigue and sleepiness,
the location of the occurrence of discomfort or pain, perceived the number of
awakenings, the degree of easily falling asleep, mattress stability. The subjects
also needed to provide 7-level VAS scores each morning reflecting the comfort
degree of different parts of human body.
(4) Selection of mattress: Eighteen mattresses were provided by Nanjing Kirin
Co., Ltd. According to the CTBA standard, the compressive mechanical properties
of the mattresses were obtained and the rigidity of mattresses was 76.5 ±26.1 mm.
(5) Analysis: Prior research on sleep surfaces had suggested that a time frame of
up to 4 nights or more may be required before a sleeper accommodates to a new
sleeping surface in their home (Jacobson et al. 2008; Bader and Engdal 2000;
Scharf et al. 1997). Therefore, data for VAS, sleep diary, sleep structure and
movement parameters were analyzed from the fourth day to the seventh day of
sleeping on one mattress, the first three night’s record were not used. Correlations
between variables were made with Spearman. To compare sleep quality between
18 different mattresses, the F-test for each pair of variables from all the recorded
nights for the 18 mattresses conditions was used. Differences of p\0.05 were
considered significant for all statistical analyses.
11.3 Results
11.3.1 Sleep Postures
The amount of movements varied among the subjects, but the individual move-
ment pattern had some reproducibility from night to night, providing that the
activity and the stress during the day were moderate and that the subjects did not
experience discomfort or pain during the night except sleeping on the mattress
with poor stability or with top layers of too high hysteresis.
Table 11.1 gives mean values of the number of turns and adopted sleep postures
and their standard deviations of 18 experimental mattresses tested by 11 subjects.
For 11 subjects, the mean of the number of changing postures per night was 18.72.
The average amount of time per night that spent in supine posture (53.02 %) was
longer than that in lateral posture (45.88 %). The average amount of time per night
that spent in the left side posture was slightly longer than that in the right side
posture. The average amount of time per night that spent in prone posture was very
short (1.09 %).
The number of turns presents negative correlation with the average amount of
time per night that spent in supine posture and presents positive correlation with
the average amount of time per night that spent in lateral posture and prone posture
11 The Quantitative Effects of Mattress and Sleep Postures 109

(Table 11.2). There was significant negative correlation between the average
amount of time per night that spent in supine posture and lateral posture
(Table 11.2). In other words, the longer the time that spent in supine posture was,
the less the number of turns was.
11.3.2 Subjective Sleep Quality and its Factors
Sleep comfort presents positive correlation with adequate sense of sleep quantity,
the degree of easily falling asleep, the degree of easily falling asleep after awake
during sleep period time, satisfaction with mattress, body status in the next
morning, stability feeling of mattress, and had negative correlation with dreaming
Table 11.1 Mean values of the number of turns and adopted sleep postures during overnight
experiments
The number of turns Sleep postures
Supine (%) Lateral on the
left side (%)
Lateral on the
right side (%)
Lateral (%) Prone (%)
Mean 18.72 53.02 24.96 20.93 45.88 1.09
SD 7.74 16.95 13.96 13.04 16.76 3.56
Note The data in the table are the mean and the standard deviation for 18 mattresses and 11
subjects
Table 11.2 Correlation between the number of turns and sleep time in every posture
The
number
of turns
The % time
in supine
position
The % time
on the left
side
The % time
on the right
side
The % time
in lateral
position
The % time
in prone
position
The number
of turns
1-0.329
**
0.174
**
0.203
**
0.297
**
0.295
**
The % time
in supine
position
1-0.615
**
-0.533
**
-0.974
**
-0.128
**
The % time
on the
left side
1-0.244
**
0.624
**
-0.031
The % time
on the
right side
1 0.554
**
-0.023
The % time
in lateral
position
1-0.034
The % time
in prone
position
1
Note
**
Mean data are significant correlation (2-tailed) at the 0.01
110 Y. Chen et al.

quantity, perceived the number of awakening and fatigue in the next day, in which
the correlation between sleep comfort, adequate sense of sleep quantity, body
status in the next morning, satisfaction with mattress and stability feeling of
mattress was stronger than others (Table 11.3).
There were significant correlations between the lumbar comfort, the buttock
comfort, the upper leg comfort, the knee comfort and the lower leg comfort,
especially the comfort of adjacent parts of human body shows closer relationship
(Table 11.4).
11.3.3 The Correlations Between the Mattress Mechanical
Characteristic and Sleep Quality
There were significant differences in the subjective sleep ratings scores (Fig. 11.1)
among 18 tested mattresses. There was a mild trend showing that the subjective
sleep quality increased as mattress firmness decreased, although most of the
subjects felt a little too soft for some of the experimental mattresses in the adapted
period (prior to the test).
11.4 Discussion
The influence of different postures (Dolan et al. 1988) is an important determinant
of human body support. Optimizing body posture in both conscious and uncon-
scious ways ensures continuous spine protection (Farfan and Gracovetsky 1984)
.
But instead of creating perfect conditions to allow optimizing our body position in
an unconscious way, the sleep system actually forces us into a certain position.
Body position is therefore limited to an initial conscious selection and subsequent
unconscious optimization. Furthermore, posture changes are necessary to avoid
pressure overloading of soft tissues and to prevent muscle stiffness. During sleep a
local ischemia—a deficiency of blood or oxygen supply—will arise in body zones
that are in contact with the sleep system. This ischemia generates metabolic
substances that stimulate the sensible nerve extremities, which will cause the
person to change his or her posture before it gets painful (Dzvonik et al. 1986).
The main advantage of sleeping in a supine position is the fact that body weight
is distributed over a large surface, resulting in pressure distribution and stability
being optimized. The lumbar part of the vertebral column will mostly be posi-
tioned between a smoothed lordosis and a slight kyphosis, depending on (1) the
kind of sleep system, (2) the natural curves of the spine, and (3) muscle tension
while sleeping. When a mattress is too soft, places where body weight is
concentrated (e.g., the hip zone) will sink deeply into the mattress. Some muscles
may be well relaxed in this position, but the spine certainly will not; the pelvis will
11 The Quantitative Effects of Mattress and Sleep Postures 111

Table 11.3 Correlation between the parameters of subjective sleep quality
SC ASSQ DEFA DQ NA DEFAA SM BSNM FND SFM
SC 1 0.625
**
0.333
**
-0.291
**
-0.281
**
0.303
**
0.493
**
0.616
**
-0.454
**
0.443
**
ASSQ 1 0.315
**
-0.113
**
-0.138
**
0.211
**
0.376
**
0.531
**
-0.428
**
0.376
**
DEFA 1 0.065 -0.111
**
0.249
**
0.258
**
0.299
**
-0.207
**
0.512
**
DQ 1 0.240
**
-0.035 -0.180
**
-0.297
**
0.221
**
-0.382
**
NA 1 -0.253
**
-0.125
**
-0.199
**
0.176
**
-0.561
**
DEFAA 1 0.194
**
0.258
**
-0.327
**
0.499
**
SM 1 0.575
**
-0.275
**
0.458
**
BSNM 1 -0.419
**
0.298
**
FND 1 0.266
**
SFM 1
Note
**
Mean data are significant correlation (2-tailed) at the 0.01
SC sleep comfort, ASSQ adequate sense of sleep quantity, DEFA the degree of easily falling asleep, DQ dreaming quantity, NA perceived the number of
awakening, EFAA the degree of easily falling asleep after awake during sleep period time, SM satisfaction with mattress, BSNM body status in the next
morning, FND fatigue in the next day, SFM stability feeling of mattress
112 Y. Chen et al.

Table 11.4 Correlation between parts comfort of human body in the next morning
Neck
comfort
Arm
comfort
Shoulder
comfort
Back
comfort
Lumbar
comfort
Buttock
comfort
Upper leg
comfort
Knee
comfort
Lower leg
comfort
Neck comfort 1 0.419
**
0.459
**
0.289
**
0.166
**
0.312
**
0.338
**
0.256
**
0.319
**
Arm comfort 1 0.494
**
0.275
**
0.129
**
0.435
**
0.427
**
0.300
**
0.301
**
Shoulder
comfort
1 0.301
**
0.211
**
0.310
**
0.355
**
0.271
**
0.302
**
Back comfort 1 0.413
**
0.319
**
0.241
**
0.158
**
0.184
**
Lumbar comfort 1 0.312
**
0.221
**
0.165
**
0.213
**
Buttock comfort 1 0.656
**
0.388
**
0.495
**
Upper leg
comfort
1 0.647
**
0.730
**
Knee comfort 1 0.737
**
Lower leg
comfort
1
Note
**
Mean data are significant correlation (2-tailed) at the 0.01
11 The Quantitative Effects of Mattress and Sleep Postures 113

cant backward resulting in a complete and unnatural lumbar kyphosis. When a
sleep system is too firm, the lumbar part of the vertebral column will not smoothen
immediately when lying down, and no contact will be made between the lumbar
part of the back and the mattress. Upon muscle relaxation (which occurs after 10 to
15 min on average) the pelvis will cant backward slightly, which results in a slight
smoothing of the lumbar part of the vertebral column. Some persons might
however experience discomfort due to muscle tension that arises when the pelvis
cants backward while the legs stay in a horizontal position (Haex 2005).
The lateral position is the most sleeping posture that European adopted, and it is
able to support the human spine correctly when both the bed and pillow are well
conceived: the spinal column is a straight line when projected in a frontal plane,
while natural curves are maintained. Due to decreased contact surface and the
center of gravity being more elevated, a lateral position is an unstable sleep
position, which can be altered by the correct positioning of the extremities.
Bending arms and legs enlarges the support area and thus improves stability.
According to our results it was found that the amount of time spent in each
sleep posture to Chinese subjects was significant different from that of European
subjects, Chinese people preferred to sleep in supine posture (53.02 % of the
amount of time spent in supine posture), while European had a preferred side to
sleep on and the amount of time spent in supine posture was less than 30 %
(Verhaert 2011). From the point of view of ergonomics, the demand of the
mechanical properties of mattresses should be different to the people with different
preferences in sleep posture.
Our results also showed that sleep quality was different when subjects slept on
spring mattresses with different characteristics of the bedding materials and
structure, and the sleep movements and posture changes was relevant to the pre-
ferred sleeping posture. Sleep quality was related to sleep comfort, while sleep
comfort was affected by the external factors such as the spirit state before sleeping
Fig. 11.1 Mean of the
subjective rating scores given
by participants in the sleep
study (overall sleep quality)
114 Y. Chen et al.

(or the degree of easily falling asleep), adequate sense of sleep quantity and
satisfaction with mattress use and so on. And sleep quality will influence badly the
body status in the next day. To the unzoned mattress, the lack of effective support
of waist and pelvic was an important factor effecting the use comfort of the
mattress.
11.5 Conclusion
These results showed the difference of sleep quality when subjects slept on
mattress with different properties. The sleep movements and change postures were
related with the sleep postures. The number of change postures was less in supine
posture than in lateral posture. The Chinese preferred the sleep posture in supine
position. Further investigations are required with the factors of the mattress
stability and instability patterns.
Acknowledgments First of all, I would like to extend my sincere gratitude to National Natural
Science Foundation of China, for her research funding on my thesis (31070503/C160302).
Without that, this project could not develop smoothly. I am also deeply indebted to all partici-
pants in the completion of the experiment for their direct and indirect help to me.
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