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Does Mattress Zoning Affect the Biomechanics of Sleep?

Authors:

Abstract

Background A third of our lifetime is spent in bed [1], so to achieve improved quality of sleep it is vital to establish optimal sleeping conditions. A sleep system’s main function is to support the body in such a way that the muscles and intervertebral discs are able to recover from an almost continuous load throughout the day. This allows the pressure to be relieved from the intervertebral discs and surrounding musculature, therefore initiating recovery, rehydration and regeneration of elasticity within soft tissues [2-3]. Failure to achieve a state of recovery can lead to the onset of Lower Back Pain (LBP), which is said to have effected 2/3 adults within the UK, and as many as 2.5 million people on a daily basis. There are a variety of mechanisms said to reduce LBP and subsequently improve the quality of sleep including improved spinal alignment, and the reduction of pressure at main contact areas between the body and the mattress [4-6]. Whilst varying comfort layers and mattress firmness can help to address these mechanisms of LBP, mattress zoning is one of the latest developments in pocket sprung mattress design aiming to improving sleep quality and reducing LBP, and thus this study explored the biomechanical differences between a zoned (Z) and non-zoned (NZ) mattress on humans. Methods Twelve healthy participants (aged 35.9±13.1 years) were recruited and screened using the Red flags screening questionnaire [7]. Ten QualisysTM Oqus7 cameras recorded movement of the spine in 6 degrees of freedom using a multisegment spine model [8] during side lying. Z and NZ 1000-count pocket sprung mattresses, topped with a minimal comfort layer were used. Additional subjective measures of Mattress comfort and firmness taken, whilst pressure distribution was measured at the hip and shoulder (Tekscan, MA, USA). Results A significantly higher peak hip pressure (2.92kPa) was noted for the Z mattress compared to the non-zoned (2.63kPa; p=0.004). No significant differences in peak pressure at the shoulder were noted between the two mattresses. There was no significance relating to perceived mattress firmness or comfort (p=0.524 and p=0.537 correspondingly). Spinal posture was measured in terms of how far posture varied from a neutral position. Within the sagittal plane there were significant differences between the Z and NZ mattresses at the UL-LL region (p=0.046) with the Z mattress deviating the least. Similarly, within the coronal plane the UT-MT (p=0.038) and LT-UL (p=0.024) posture demonstrated statistically significant improvements. The Z mattress demonstrated less rotation within the LL-PEL segment of the spine (p=0.012), however it displayed significantly poorer results within the LT-UL and UL-LL segments (p=0.026 and p=0.016 respectively). Discussion There is evidence to suggest that whilst a zoned mattress does not disperse pressure as effectively at the hip, it is in fact more supportive to compensate as it reduces “hammocking” and improves overall spinal alignment. The zoned mattress outperformed the non-zoned mattress in key areas around the lower lumbar to pelvic region suggesting that it may help to reduce torsional strains, potentially helping individuals with LBP. It is evident from this data that a multi-factoral approach is beneficial in understanding our interaction with sleep surfaces.
DOES MATTRESS ZONING AFFECT THE
BIOMECHANICS OF SLEEP?
Laurence Smith, Ambreen Chohan, Jim
Richards
Allied Health Research Unit, University of Central
Lancashire, United Kingdom
Background
A third of our lifetime is spent in bed [1], so to
achieve improved quality of sleep it is vital to
establish optimal sleeping conditions. A sleep
system’s main function is to support the body in
such a way that the muscles and intervertebral
discs are able to recover from an almost
continuous load throughout the day. This allows
the pressure to be relieved from the intervertebral
discs and surrounding musculature, therefore
initiating recovery, rehydration and regeneration of
elasticity within soft tissues [2-3]. Failure to
achieve a state of recovery can lead to the onset
of Lower Back Pain (LBP), which is said to have
effected 2/3 adults within the UK, and as many as
2.5 million people on a daily basis. There are a
variety of mechanisms said to reduce LBP and
subsequently improve the quality of sleep
including improved spinal alignment, and the
reduction of pressure at main contact areas
between the body and the mattress [4-6]. Whilst
varying comfort layers and mattress firmness can
help to address these mechanisms of LBP,
mattress zoning is one of the latest developments
in pocket sprung mattress design aiming to
improving sleep quality and reducing LBP, and
thus this study explored the biomechanical
differences between a zoned (Z) and non-zoned
(NZ) mattress on humans.
Methods
Twelve healthy participants (aged 35.9±13.1
years) were recruited and screened using the
Red flags screening questionnaire [7]. Ten
QualisysTM Oqus7 cameras recorded movement
of the spine in 6 degrees of freedom using a
multisegment spine model [8] during side lying. Z
and NZ 1000-count pocket sprung mattresses,
topped with a minimal comfort layer were used.
Additional subjective measures of Mattress
comfort and firmness taken, whilst pressure
distribution was measured at the hip and shoulder
(Tekscan, MA, USA).
Results
A significantly higher peak hip pressure (2.92kPa)
was noted for the Z mattress compared to the
non-zoned (2.63kPa; p=0.004). No significant
differences in peak pressure at the shoulder were
noted between the two mattresses. There was no
significance relating to perceived mattress
firmness or comfort (p=0.524 and p=0.537
correspondingly).
Spinal posture was measured in terms of how far
posture varied from a neutral position. Within the
sagittal plane there were significant differences
between the Z and NZ mattresses at the UL-LL
region (p=0.046) with the Z mattress deviating the
least. Similarly, within the coronal plane the UT-
MT (p=0.038) and LT-UL (p=0.024) posture
demonstrated statistically significant
improvements. The Z mattress demonstrated less
rotation within the LL-PEL segment of the spine
(p=0.012), however it displayed significantly
poorer results within the LT-UL and UL-LL
segments (p=0.026 and p=0.016 respectively).
Non-Zoned Zoned
Sagittal
UT-MT 13.23
(±8.3)
12.83
(±7.4)
MT-LT -2.78
(8.5)
-0.99
(±7.5)
LT-UL 0.68
(±6.7)
0.45
(±6.4)
UL-LL -14.95
(±9.1)*
-13.80
(±7.8)*
LL-PEL -0.39
(±6.1)
-0.35
(±5.4)
Coronal
UT-MT -1.24
(±3.8)*
-0.46
(±3.1)*
MT-LT 2.78
(±4.1)
2.29
(±2.9)
LT-UL 3.29
(±2.9)*
2.94
(±2.9)*
UL-LL 0.54
(±5.5)
0.34
(±3.8)
LL-PEL 6.03
(±3.3)
5.39
(±3.7)
Transverse
UT-MT 5.21
(±5.9)
5.44
(±5.0)
MT-LT 1.63
(±4.2)
1.81
(±4.1)
LT-UL 0.31
(±2.4)*
0.87
(±1.7)*
UL-LL -2.89
(±4.3)*
-3.96
(±3.3)*
LL-PEL 1.59
(±4.7)*
0.69
(±4.4)*
Table 1: Spinal data showing change (degrees)
from a neutral posture (UT=Upper Thoracic;
MT=Mid Thoracic; LT=Lower Thoracic; UL=Upper
Lumbar; LL=Lower Lumbar; Pel=Pelvis.
*(Significance p<0.05)
Discussion
There is evidence to suggest that whilst a zoned
mattress does not disperse pressure as
effectively at the hip, it is in fact more supportive
to compensate as it reduces “hammocking” and
improves overall spinal alignment. The zoned
mattress outperformed the non-zoned mattress in
key areas around the lower lumbar to pelvic
region suggesting that it may help to reduce
torsional strains, potentially helping individuals
with LBP. It is evident from this data that a multi-
factoral approach is beneficial in understanding
our interaction with sleep surfaces.
References
1. Gordon et al. Phys Can, 63(2), 183-90. 2011.
2. Nachemson et al. Scan J Re Med, 2(1),1-40.
1970.
3. Huysmans et al. Gait & pos, 24, 54-61. 2006.
4. Lahm et al. Ergon, 45(11), 798-815. 2002.
5. Verhaert et al. Ergon, 54(2), 169-78. 2011.
6. Lee, et al. Int. J of Ind Erg, 36, 943-49, 2006.
7. Greenhalgh et al. Churchill Livingstone. 2010.
8. Chohan et al. Bone Joint J, 95 (4), 12. 2013.
Acknowledgements
Staff time for this project was funded by a UCLan
Ideas Investment Voucher and match-funded by
Silentnight Group Ltd., UK.
... Rehabilitative measures may involve the use of medical devices, such as lumbar bracing to improve alignment and associated pain (20). But may also include simple lifestyle changes such as changing the sleeping surface to a more supportive mattress (21,22), or the introduction of a correctly fitted and supportive bra (23), which can provide important changes in alignment. Postural assessments and corrective techniques are therefore often key to the management of such patients. ...
Article
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