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INTERNATIONAL ARCHIVES OF MEDICINE
Section: PhySical Medicine and Rehabilitation
ISSN: 1755-7682
1
2015
Vol. 8 No. 170
doi: 10.3823/1769
iMedPub Journals
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© Under License of Creative Commons Attribution 3.0 License
This article is available at: www.intarchmed.com and www.medbrary.com
Abstract
Background: Our research team believes that the arrangement of
the hammock may influence the orthostatic posture. The aim of the
present study was to assess the orthostatic posture in right and left
views among hammock-users and hammock non-users of northeast-
ern Brazil.
Methods: Were included 32 healthy participants, subdivided into
two groups: hammock non-users, and hammock-users, both in the
last 10 years. The orthostatic posture was performed through photo-
grammetry analysis (PAS/SAPO). We analyzed body alignment varia-
bles: horizontal alignment of the head, vertical alignment of the head,
vertical alignment of the trunk, hip angle, body vertical alignments,
horizontal alignment of the pelvis, knee angle, and ankle angle.
Results: On the right side, there was statistically significant difference
in the horizontal alignment of the head (P = 0.04), hip angle (P = 0.02),
vertical alignment of the body (P = 0.01) and horizontal alignment of
the pelvis (P = 0.03). In the left side, there was statistically significant
difference in horizontal alignment of the head (P = 0.04) and the
horizontal alignment of the pelvis (P = 0.04).
Conclusion: Sleeping in the hammock influenced the orthostatic
posture, especially in horizontal alignment of the head, hip angle, the
vertical alignment of the body and horizontal alignment of the pelvis
in the side views. Our data open new possibilities of research in this
area, which has been obscure until this moment, and enable the in-
dication or contraindication to sleep in hammocks.
Influence Of Sleeping In
Hammocks On The Orthostatic
Posture
ORIGINAL
Antonio de Pádua Rocha
Nóbrega Neto1, Felipe
Rodolfo Pereira da Silva2,
Any Carolina Cardoso
Guimarães Vasconcelos3,
Amélia Pasqual
Marques4, Baldomero
Antônio Kato da Silva5,
Daniel Fernando Pereira
Vasconcelos5*
1 Master Student, Post Graduate Program
in Biomedical Sciences, Federal
University of Piaui, Parnaiba – PI,
Brazil.
2 Biomedical Scientist, Federal University
of Piaui, Parnaiba – PI, Brazil;
3 Assistant Professor, Department of
Physical Therapy, Mauricio Nassau
College, Parnaiba – PI, Brazil.
4 Associate Professor, Department of
Physical Therapy, Speech Therapy
and Occupational Therapy, Faculty of
Medicine, University of São Paulo, São
Paulo, Brazil.
5 Adjunct Professor; School of
Physiotherapy, Federal University of
Piaui, Parnaiba-PI, Brazil.
Contact information:
Daniel Fernando Pereira Vasconcelos
Universidade Federal do Piauí – UFPI;
Campus Ministro Reis Veloso;
Av. São Sebastião, 2819, Reis Veloso;
Parnaíba - PI – Brasil, 64204-035.
vasconcelos@ufpi.edu.br
Keywords
Sleep system,
Photogrammetry, alignment
postural, Evaluation.
INTERNATIONAL ARCHIVES OF MEDICINE
Section: PhySical Medicine and Rehabilitation
ISSN: 1755-7682
2015
Vol. 8 No. 170
doi: 10.3823/1769
This article is available at: www.intarchmed.com and www.medbrary.com
2
Background
During the sleep, the musculoskeletal system may
recover from the almost continuous loading of the
everyday life, when the human body is in sustained
contact with the sleep system (i.e., a mattress, sup-
porting structure, and hammock). The hammock is
commonly used by tropical areas as Brazil [1], and
may provide a rocking with frequency similar to
0.25Hz, which accelerates sleep onset [2].
Our research team believes that the arrangement
of the hammock may promote flexor position, and
influence the angles and distances between body
segments at a given point in time, the sleep pos-
ture. Such sleep posture can change the orthostatic
posture, common standing position, via sensory sys-
tems such as: visual, somatosensory and vestibular
[3]. Although no default approach to evaluate the
posture has been defined, the photogrammetry has
been used [4,5,6,7]. However, there is not a study
that investigates the correlation between the ham-
mock and posture.
The aim of the present study was to assess the
orthostatic posture in right and left views among
hammock-users and hammock non-users of north-
eastern Brazil.
Method
Participants
Were included 32 healthy participants, subdivid-
ed into two groups: Hammock-users (HA), in the
last 10 years (n=15/ gender: 10 males and 5 female
/ age: 30.20± 9.60 / body mass index-BMI: 27.00±
4.39) and Hammock Non-users (HN, in the last 10
years (n= 17/ gender: 8 males and 9 female/ age:
25.94± 5.83/ body mass index-BMI: 24.29± 3.23).
The study was conducted in the Federal University
of Piaui, and has been approved by the Research
Ethics Committee (0386.0.045.000-11/2011). All
participants signed the free and informed term of
consent.
The participants that presented some structural
alteration, neurodegenerative or amputation and/
or shortening of the limbs, or no ancestry from
northeastern Brazil were excluded.
Photogrammetry through PAS/SAPO®
The photogrammetry analysis was performed
through the protocol of the Postural Assessment
Software (PAS/SAPO) [5]. To summarize, for the
achievement of the images, participants were in-
dividually evaluated, in the comfortable orthostatic
posture, on a flat surface, barefoot, hair up and
wearing bathing suit. For the calibration of the im-
age in PAS/SAPO, a plumbline marked with two
polystyrene balls (15mm diameter) at a distance
of 100 cm from each other was used; black fabric
2.0x1.40 m for better visualization of the marked
points; digital camera (Cannon, IXY Digital 700
model, 7.1 megapixels, 1.4x magnification); adjust-
able tripod for camera mount; double-sided tape
to fix the polystyrene balls in the anatomical points
(Figure 1).
We analyzed the participants in two views: right
and left side. The following variables were analyzed
(Figure 1): Horizontal alignment of the head - HHA;
Vertical alignment of the head - HVA; Vertical align-
ment of the trunk – TVA; hip angle - HA; Vertical
alignment of the body - BVA; Horizontal alignment
of the pelvis - PHA; knee angle – KA; ankle angle
– AA. After the images were captured in right side
view, the carpet was rotated 180 ° to obtain the
photo in the left side view.
Statistical Analysis
For the statistical analysis we used Shapiro-Wilk
to check the normal pattern of the data, and for
parametric, and no parametric, t-student test and
Mann-Whitney, respectively were used. (BioEstat
ver.5.0, Belém, PA, Brazil). Significance level was
established at 5%.
INTERNATIONAL ARCHIVES OF MEDICINE
Section: PhySical Medicine and Rehabilitation
ISSN: 1755-7682
2015
Vol. 8 No. 170
doi: 10.3823/1769
© Under License of Creative Commons Attribution 3.0 License 3
Results
On the right side, there was a statistically signifi-
cant difference in horizontal alignment of the head
(P = 0.04), hip angle (P = 0.02), vertical alignment
of the body (P = 0.01), and the horizontal alignment
of the pelvis (P = 0.03), as seen in table 1.
On the left side, there was a statistically signifi-
cant difference in the horizontal alignment of the
head (P = 0.04) and horizontal alignment of the
pelvis (P = 0.04) (Table 2).
Discussion
This study is the first, according to our knowl-
edge, that compared orthostatic posture among
hammock-users and hammock non-users, and our
data demonstrated that hammock-users influenced
significantly the orthostatic posture, in the horizon-
tal alignment of the head, hip angle, vertical align-
ment of the body, and horizontal alignment of the
pelvis in the right side view, horizontal alignment
of the head, and horizontal alignment of the pelvis
Figure 1: This figure shows the anatomic points, and variables analized throuh photogrammetry. 1) tra-
gus, 2) spine process of C7, 3) acromion, 4) anterior-superior iliac spine, 5) posterior-superior
iliac spine, 6) femur, greater trochanter, 7) knee, articular line, 8) lateral malleoli. The variables
analyzed were: HHA - Horizontal alignment of the head, HVA - Vertical alignment of the head,
TVA - Vertical alignment of the trunk, HA - Hip angle, BVA - Vertical alignment of the body,
PHA - Horizontal alignment of the pelvis, KA - Knee angle, and AA - Ankle angle. Angles
represented in red showed significant difference, and angles represented in blue denoted no
statistical significance between hammock-users and hammock non-users.
INTERNATIONAL ARCHIVES OF MEDICINE
Section: PhySical Medicine and Rehabilitation
ISSN: 1755-7682
2015
Vol. 8 No. 170
doi: 10.3823/1769
This article is available at: www.intarchmed.com and www.medbrary.com
4
in left side view (Table 1 and 2). Age and BMI of
all subjects were not significantly different between
groups (P > 0.05). Such data suggest that the age
and the BMI of individuals did not contribute with
statistical difference observed in the angles.
Horizontal alignment of the head can indicate the
position of the head relative to the trunk, when
these values are decreased there is an indication
that the head is inclined forwards [8]. The arrange-
ment of the hammock in an arc promoted extend-
ed time for hammock-users in the same position,
decreasing the angle of horizontal alignment of the
head. However, the hammock non-users showed
an increase in this angle, with their heads positioned
posteriorly. The hammock arrangement does not
stimulate changes in position and body movement.
Table 2. Variables analyzed through photogrammetry on the left side.
Variables
Mean± SD
P value
HN HA
Horizontal alignment of the head a 47.50± 3.27 43.97± 5.87 0.04*
Vertical alignment of the head b20.02± 6.66 18. 6 4± 7. 9 8 0.76
Vertical alignment of the trunk b-1.08± 1.99 -1.18± 1.85 0.82
Hip Angle b-8.89± 3.62 -10.83± 6.25 0.36
Vertical alignment of the body a2.72± 0.97 2.9 4± 1.0 6 0.55
Horizontal alignment of the pelvis a-13.75± 4.25 -10.71± 4.25 0.04*
Knee Angle b-4.82± 4.38 -7.16 ± 8 .70 0.38
Ankle Angle b87.01± 3 . 41 87. 50 ± 4.13 0.92
* indicates statistically significant difference. a tested by t-student test. b tested by Mann-Whitney. HN, Hammock Non-users;
HA, Hammock-users.
Table 1. Variables analyzed through photogrammetry on the right side.
Variables Mean± SD P value
HN HA
Horizontal alignment of the head 47. 61± 4 . 41 43.93± 5.68 0.0 4*
Vertical alignment of the head 21.10± 7.77 16.47± 6.98 0.08
Vertical alignment of the trunk -1.57± 2.26 -1.6 6± 1.98 0.90
Hip Angle -7.11 ± 3 . 9 0 -10. 4 8 ± 4.15 0.02*
Vertical alignment of the body 1.81± 0 .9 5 2.62± 0.78 0.01*
Horizontal alignment of the pelvis -13.51± 4.55 -10.03± 4.02 0.03*
Knee Angle -2.62± 4.72 -5.96± 5.22 0.06
Ankle Angle 87.09± 3.44 8 7.16 ± 2 . 76 0.94
* indicates statistically significant difference. All variables were tested by t-student test. HN, Hammock Non-users; HA,
Hammock-users.
INTERNATIONAL ARCHIVES OF MEDICINE
Section: PhySical Medicine and Rehabilitation
ISSN: 1755-7682
2015
Vol. 8 No. 170
doi: 10.3823/1769
© Under License of Creative Commons Attribution 3.0 License 5
It seems even to distribute pressure on the bony
prominences on the surface of the hammock, al-
lowing the subject to remain longer in the same
position, unlike a plane surface [9].
A study suggests that pain in the body may be
associated with the sleeping position [10]. Our data
open new possibilities regarding the indication and
contraindication for the use of the hammock.
Therefore, its dynamics during sleep and the dis-
tribution of body pressure are different from other
sleep systems.
Hip angle checks the position of the hip joint in
relation to the flexion and extension. Body arrange-
ment in the hammock may change the anterior and
posterior muscular chains.
The vertical alignment of the body shows the
anterior and posterior body inclination according
to the vertical line. Even though our data showed
significant differences in this angle, we similarly be-
lieve in the study [11] investigating that the mat-
tress inflation pressure induced significant changes
in the spinal alignment in normal subjects during
sleep, but these values were of little physiological
and clinical consequence. However, our data supply
basic information necessary to evaluate similar cor-
relations in other groups of individuals.
The horizontal alignment of the pelvis checks the
angle of the pelvis, and is in a direct relation be-
tween the lumbar spine biomechanics, pelvis and
hip [8]. In this way, hammock-users showed signifi-
cantly decreased values for horizontal alignment of
the pelvis, suggesting that it may compromise mus-
cle groups and tissues corresponding to the contact
surface.
The exact role of the hammock in the orthostatic
posture is not yet clear. According to our data, it
is acceptable that the hammock may influence on
the orthostatic posture, because this sleep system
is different in the following aspects: the rocking,
the arrangement, the pressure over the bony prom-
inences, the body movements and change positions
during the sleep, and others that still remain ob-
scure. Our research team demonstrated that the
arrangement of the hammock may promote flexor
position, and influence the angles and distances be-
tween body segments.
Conclusion
Sleeping in the hammock influenced the orthos-
tatic posture, especially in the horizontal alignment
of the head, hip angle, vertical alignment of the
body and horizontal alignment of the pelvis in the
side views. Our data open new the possibilities of
research in this area, and enable the indication or
contraindication for the sleep in hammocks.
Competing interest
We declare no conflict of interest.
Author’s contribution
APRNN, ACCGV and FPRS participated in the ac-
quisition of data and wrote the manuscript. APRNN
interpreted the data and drafted the manuscript.
DFPV, APM and ACCGV determined the design
and drafted the manuscript. BAKS, DFPV and APM
review of the manuscript. All authors read and gave
final approval for the version submitted for publi-
cation.
Acknowledgments
Research supported by the Federal University of
Piaui (UFPI – Edital PIBIC 2013/2014 and BIAMA
03/2014). We thank teacher Abilio Borghi for the
grammar review of the manuscript.
INTERNATIONAL ARCHIVES OF MEDICINE
Section: PhySical Medicine and Rehabilitation
ISSN: 1755-7682
2015
Vol. 8 No. 170
doi: 10.3823/1769
This article is available at: www.intarchmed.com and www.medbrary.com
6
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