Osteology Unit, Derer’s University Hospital and Policlinic Bratislava, Slovakia, head Ass. Prof. Jaroslava Wendlová, MD, PhD.
Vnitř Lék 2010; 56(7): 759-763
80th Birthday - Jaroslava Blahoše, MD, DrSc.
Based on a simple biomechanical analysis, available to physicians, the article recommends carrying a backpack regularly as a part of the complex rehabilitation of osteoporotic patients. Carrying a backpack in front or on the back is recommended for patients with uncomplicated osteoporosis, carrying a backpack only on the back is recommended for patients with osteporotic vertebrae fractures. The importance of carrying a backpack is based upon remove the muscular dysbalance of the trunk muscles and upon increasing the bone strength by compressive force acting upon the vertebrae and proximal femur and activating osteoblasts to osteoformation. The backpack load magnitude is differentiated – patients with vertebrae fractures put a weight up to 1 kg into the backpack, patients without vertebrae fractures up to 2 kg.
The aim of this short statement is to explain the benefits of
carrying a backpack in the rehabilitation
of osteoporotic patients on the basis of a simple biomechanical analysis
available to physicians.
Carrying a backpack
alternately in front and on the back is recommended for patients:
with vertebral ostepenia and
osteoporosis (without vertebrae fractures) and muscular dysbalance of the trunk
muscles (fig. 1),
effect: remove the muscular
dysbalance of the trunk musculature, activating osteoblasts to neoformation of
bone by compressive forces acting upon vertebrae [1–5], increasing the bone
with osteopenia and osteoporosis
in the area of proximal femur,
effect: stimulation of
osteoblasts to osteoformation by compressive forces acting upon the area of
proximal femur [1–5], increasing the bone strength.
Carrying a backpack on the back only:
for patients with osteoporotic
vertebrae fractures .
Patients with osteoporotic vertebrae fractures
fractures represent the most frequent complication of osteoporosis and
contribute to a partial or full invalidation of patients. Kyphosis, as
a consequence of wedge-shaped deformation of fractured osteoporotic
vertebrae in the thoracic or lumbosacral area, conditions biomechanical
changes in the organism with consequent grave clinical symptomatology:
deviation of body’s gravity
centre from its normal position (fig. 2a),
muscular dysbalance of trunk muscles,
ileocostal friction syndrome (the
rib arches rub on ala ossis ilii by walking and by motion) (fig. 3),
pathological position of disci
intervertebrales in the kyphosis and their non‑physiological
load (decrease of compressive forces upon ventral part and decrease of tension
forces upon dorsal part of intervertebral discs),
growth of compressive forces upon
development of cor pulmonale
ischemia or venostasis in
intraabdominal organs, non‑specific intermittent abdominal pain, chronic
chronic backache .
It is recommended to carry
a backpack on the back for patients with osteoporotic fractures. The
following positive effects can be achieved:
careful stretching of shortened
strengthening the stretched and
weakened dorsal muscles (balancing the muscular dysbalance),
potentiating a moderate
straightening of a spine and so mild the ileocostal friction syndrome and
reducing tension forces acting upon dorsal muscles,
reducing compressive forces
acting upon organs of abdominal cavity,
displacement of the deflected
gravity centre closer to its physiological position – improving the
reducing compressive forces
acting upon ventral part and tension forces acting upon dorsal part of
intervertebral discs in the site of pathological kyphosis,
rise of the maximal breathing capacity,
restriction of pain intensity in
the back .
Impaired stability of body in osteoporotic patient with
fractured vertebrae (explanation
to fig. 2a and 2b)
From the mechanical point
of view the balance constancy in any posture of a man is determined
the magnitude of the support
the position of the body’s gravity centre in relation to the
distance of the body’s median (the gravity centre projection) from the
edge of the support area,
magnitude of the stability angle.
area of a man is represented by the area delimited by the outer limit
of the body’s contact area with the ground. The outer limit of this support
area is called the edge of the support area or the stability limit.
The gravity centre (T) of the body is represented by a mass
point, concentrating the whole force of the body’s gravity (the body mass). It
is called also the mass centre. The body mass is equally distributed from this
point to all sides. The median (t) is a vertical line
passing through the gravity centre. The gravity centre projection (PT)
is the point in the support area, crossed by the median.
The stability angle is the angle formed by the median and the line
passing through the gravity centre and the edge of the body’s support area.
of the skeleton is increased by:
enlargement of the support area,
of the gravity centre to the support area,
approximation of the median (gravity centre projection) to the centre of the
enlargement of the stability angle.
gravity centre projection gets over the edge of the support area, i.e., beyond
the stability limit, the man is in an unbalanced position and falls down to the
ground. In patients with osteoporotic vertebral fractures the projection of the
gravity centre into the support area gets close to the stability limit of the
support area in the upright position, and so these patients are prone to falls
when bending forward or to sides .
Biomechanical analysis [7–9]
The importance of carrying a backpack
can be explained by a simple biomechanical model, represented in fig. 4 and 5.
The force F, situated in front of vertebrae, simulates the external load
(e. g., a backpack, worn in front). To
determine the way, how the force F is transferred into the vertebrae,
the model example is solved by situating a couple of forces in the axis of
vertebrae. The couple of forces are two forces of the same magnitude, acting in
the same ray and in the same point of application, however, they are of the
opposite direction and sense, while it holds true that:
F = F1 = F2
equilibrium status of forces does not change, as the effects of both added
forces are mutually cancelled. This couple is also called the couple of zero
Forces F1 and
F2 produce a positive bending moment M on
the arm r (acting clockwise) and the force F2 is
transferred as compressive force into lower situated vertebrae and through both
hip joints into both lower limbs.
load by the force F is transferred to the vertebrae as a bending
moment M and compressive force F2.
the backpack regularly (about an hour daily) and alternatingits position in front and on the back
balances the muscular dysbalance of the torso musculature. Simultaneously, the compressive force in the vertebrae and in the
proximal femur area is increased. The compressive force stimulates
osteoblasts to production of bone tissue (activation of oesteoformation),
increasing so the bone strength.
According to all, that we can not calculate
safe load for patient, we do not know the ultimate strength limit for
osteoporotic and fractured vertebra in vivo, we can recommend only the very
patients with vertebrae fractures put a load of up to 1 kg into their backpacks , the patients
without vertebrae fractures up to 2 kg.
Carrying a backpack in front
The backpack simulates the external load,
stressing the spine to bend and press. The body defends itself against the
bending moment of the backpack’s gravity force (M), pulling the trunk to
bend forward, by firstly isometric contraction of the abdominal and less dorsal
muscles. These muscles are strengthened and the compressive force (F2)
is symmetrically (if the pelvis is in horizontal line) distributed from the
spine through hip joints into both lower limbs. Carrying a backpack in
front makes, at the same time, the shortened pectoral muscles to stretch
Carrying a backpack on the back
The body defends itself against the bending
moment of the backpack’s gravity force (M), pulling the trunk to bend
backwards, by firstly isometric contraction of the dorsal muscles and less
abdominal muscles, and in doing so, strengthens them. The backpack’s gravity
force also carefully stretches the shortened pectoral muscles and the
compressive force (F2) is also symmetrically distributed from
the spine through the hip joints into both lower limbs [6,11].
In the Fig. 4 the force F
(external load) will be situated in the back of the spine and the bending
moment M will be negative (acting counter – clockwise).
Carrying a backpack regularly
represents for the patient with uncomplicated osteoporosis as well as for the patient with
osteoporotic vertebrae fractures a low-cost, easily accessible and
effective daily rehabilitation, which is a part of a complex
kinesitherapy of the patient. It allows the patient to carry a backpack
while making a small shopping, walking in a park or in easy terrain.
It is necessary to be aware that during the combination of carrying a back-pack and Nordic walking certain magnitude of
compressive forces is transferred from the patient into the poles and the
rehabilitation effect of carrying a backpack is diminished .
Declaration – conflict of
The author declares, that she has no competing interests
(financial or non financial).
Fig. 1 and 3 are modified by author from
original anatomical pictures. Fig. 2a,
2b, 4, 5 are original – created by author.
Ass. Prof. PhDr. Bohuš Hatiar, CSc. and Martin Petrik
do redakce: 17. 5. 2010
Prof. Jaroslava Wendlová, MD, PhD.
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