Musculoskeletal disorders (MSDs) are the impairments of both the muscular
system as well as the skeletal system including a wide range of diseases and
syndromes, which are usually associated with pain and discomfort. The term
musculoskeletal disorder denotes ‘ health problems of the locomotor
apparatus, i.e. muscles, tendons, the
skeleton, cartilage, the vascular system, ligaments and nerves’. (World Health Organization 2003, David G., 2000)
They occur predominantly in the back, neck, upper extremities, and
in some cases, lower extremities (Abledu et al., 2014).
MSDs cover a wide range of inflammatory and
degenerative diseases of the locomotor system (The World Health Organization,
2003) including inflammations of tendons (tendinitis and tenosynovitis ,
rotator cuff tendonitis , Biceps tendonitis) , myalgias, i.e. pain and
functional impairments of muscles , compression of the nerves &
degenerative disorders occurring in the spine.
Major causes of MSDs are due to bodily reaction/
bending, climbing, crawling, reaching, twisting, overexertion, or
repetitions. Work related MSDs do not
include disorders caused by slips, trips, falls, motor vehicle accidents. (David J. Magee et
al., 2009).
Work-related musculoskeletal disorders are a cause of
concern not only because of the health effects on individual workers, but also
because of the economic impact on businesses and the social costs. Figures from Austria, Germany
& France, demonstrate an increasing impact of musculoskeletal disorders on
costs. In France (2006), MSDs have led to seven million workdays lost, about
710 million EUR of enterprises contributions
(Buckle P. et al., 1999).
The commuting ‘long distance driving’ is
defined as ‘ long ranges from 45 km and more (van Ham et al. 2001), to
100 km and more ’(Abrahamsson 1993, Statistics Swe-den 1996).
Schwanen & Dijst (2002) concluded on an average, individuals spend about ten
percent of their daily working hours on commuting, which would make almost 60
minutes round the trip for an 8-hour workday.According to the findings, 49% of respondents
in India spend at least 12 hours (half-a-day) or more than 100 minutes every
day driving their cars. About 14% respondents have admitted spending up to
three hours behind the wheel every day.(Times of India Feb 2015).
These long hours of driving often lead to many respiratory, musculoskeletal, peripheral
nervous, cardiovascular, gastrointestinal diseases. Rates of trauma accidents
are also high. More than 50% of all drivers suffer from musculoskeletal
disorders, which are manifested through tension, pain and decreased work
capacity. Thirty one percent of the auto-transport employees had complaints
about their health. Functional complaints about musculoskeletal (46.2%),
respiratory (22.7%), gastrointestinal (17.3%), and the central nervous system
dysfunction (32.7%) were prevailing (Obelenis at al., 2003)
Babajide et al., 2012 conducted a study to find the
prevalence of work related musculoskeletal disorder among occupational taxi cab
drivers and they found that Significant prevalence of WRMD reported among
respondents on the four body segments are located at the neck (67%), right and
left wrists (18%, 20%), upper, middle and lower back (29%, 29%, 30%), and
buttock (19%) of the operators.
Absenteeism, turnover and disability among the drivers
appeared to be high when compared to any
other occupation. Almost 90 per cent of drivers with high work experience (over
18 years) left jobs for reasons of poor health. The main conditions leading to
disablement among drivers are related to
cardiovascular diseases, musculoskeletal problems and psychosomatic disorders ,
psychological problems (fatigue, tension, mental overload) cancers, gastro intestinal,
& sleeping problems (Kompier et al., 1996; Whitelegg et al., 1995.)
PATHOMECHANICS
The driver-motor
vehicle system is a complex system that involves the interaction of human,
technological systems and their environment (Nasrin et al., 2012). Faulty
design of driver’s workplace has been identified as a major risk factor
responsible for the uncomfortable conditions which operators of motor vehicles
are exposed to while driving especially for a long period ( Onawumi &
Lucas., 2012).
In the study by
Magnusson et al (1996), back and neck pain among urban drivers was
significantly related to ergonomics, such as poor seat adjustment, steering and
braking problems, as well as long, uninterrupted hours behind the wheel. In
order to handle a vehicle car drivers must sit in a rigid, upright position
that, if held for long periods of time, leads to stiffening of the neck, back,
and muscles of the extremities. If a car is not moving, then sitting in a
driving seat is not significantly different than sitting on a padded chair. As
soon as the vehicle starts moving, however, conditions change dramatically. The
average vertical force applied by the hands to the steering wheel was 38 N
(downward) and the average horizontal force was 8.4 N (rearward) ( Benstowe et
al., 2008).While a vehicle is in motion the body is subject to different forces
of acceleration and deceleration, lateral swaying from side to side and
whole-body up and down vibrations (Benstowe et al., 2008) .When driving, the
feet are being used actively, moving from the fuel pedal to the brake, and in a
stick-shift vehicle, the left foot manages the clutch. When the feet are active
they cannot be used to support and stabilize the lower body as normally happens
when they are placed on the floor during normal sitting. This prolonged and
repetitive micro traumas while driving lead to irritation of tendons , muscle
fatigue , ischemia , oedema and heat
thus, inflaming the synovia and bursa triggering the physiological responses of
surrounding fibrous tissues eventually causing muscle contracture which in turn
decreases the joint mobility , tendon motion and muscle strength causing functional disability in long driving.
In view of the fact
that the drivers who spend long times behind wheels, MSDs are progressively
formed over time; which may have considerable impacts on their personal and
social life. The evidence showed that the people driving at least half of
working hours each day suffer three times more than other workers (Waersted et
al., 2010).
Head and Neck
Faulty design of
driver’s workplace and poor sitting posture are parts of what are responsible
for stresses and strains imposed by the uncontrollable conditions of the
elements of workplace on drivers (Blangsted et al., 2008). During driving, the
drivers work in awkward body posture, sometime slouch posture, often
accompanied by repetitive movements of both upper extremities & neck.The
plausible mechanism for the strong relation between prolonged driving and neck
pain is due to a continuous static load on the neck muscles, while
sitting(Linton & Tulder, 2001).Static loading of the neck muscles will
induce biomechanical strain for example, an increased muscle tone which may in
the long term lead to the development of neck pain (Ariens et al., 2000) .
Furthermore, Preuschen
and Dupuis (1969) recommended a neck angle larger than 20° to the vertical
causes tension in the deep muscles of the neck & ischemia in the brain.
Additionally, for angles larger than 20° vibrations from the buttocks to the
neck are amplified, which causes a
higher strain on neck and head (Preuschen and Dupuis,1969). Harrison et
al. (2000) reported that a backrest angle of 120° generates an abnormal neck
angle of 30° and eventually leads to strain on the neck musculature while
driving.
Shoulder
Most driving conditions caused moderate (30%)
to high activation (50%) of supraspinatus
& deltoid with some moderate activation of infraspinatus. The middle deltoid is
the most active muscle in maintaining
the arm in a raised position while driving (Ackland et al., 2008) the supraspinatus and long head of
biceps also support the weight of the arm while applying a well-directed line
of action for centralising the humeral head on the glenoid (Ackland and Pandy,
2009); the trapezius muscles are active in maintaining the elevation of the
shoulder girdle, (Rasmussen and De Zee,
2010); infraspinatus and short head of triceps then act to actuate the steering
task, flexing the shoulder and extending the arm, respectively while driving.
It is known that a
history of trauma is the most strongly correlated factor with rotator cuff tears while driving (Yamamoto et al., 2010) and the
conclusions relating to the loading of the shoulder muscles and shoulder joint
are relevant to the very large population that regularly drive ( 38 million
driving licenses held in the UK; data.gov.uk, 2013), regardless of age.
Shoulder muscle activations are strongly and positively correlated with the
steering resistance torque (Pick and Cole, 2006). Repeated high muscle
activation could lead to muscle fatigue or even overload; particularly since
supraspinatus and deltoid are potentially loaded eccentrically (Lieber and
Friden, 1993; Proske and Morgan, 2001). Moreover, these muscles presented
nearly two times higher activation than any other muscle of the upper limb;
therefore, injury to one of these muscles might lead to a dangerous increase of
the activation of the other muscles to compensate. As supraspinatus and deltoid
act together, injury or weakness in one of these muscles may mean that the
other muscle will be unable to compensate for the load due to the already high
activation when both muscles are functioning normally. This may have
implications for joint instability, particularly in the case of the
supraspinatus and hence leading to severe disability in driving.
Low back
The backward rotation
of the pelvis occurs when seated in a car, the moment arm between the Center of
Gravity and the lumbar vertebrae increases, and more tension is produced in the
Erector spinae muscles and other passive ligament structures (Chaffin et al.
2006). This change in curvature is believed to reduce the load bearing capacity
of the lumbar spine and puts the structure at higher strains during sitting. If
the spine is exposed to postural stresses for long enough, it stiffens as well
as shortens (creep effect-when the compressive load exceeds the osmotic
pressure in the disc, fluid is slowly expelled and the disc becomes less
compliant and shortened). Also, muscular activities required to maintain given
posture may induce symptoms of fatigue. LBP increases with vibrations and cause
herniated nucleus pulposus in drivers with the most severe long-term exposure.
Prolonged sitting is associated with constant spinal pressure & continuous
fluid exosmosis and hence can impede disc nutrition and consequently cause disc
degeneration (National Research Council and the Institute of Medicine, 2001).
Research has also shown that lumbar disc herniation may result from prolonged
sitting in the typical flexed posture. This is especially the case if sitting
occurs in motor vehicles where the vibration forces add to the stress on the
discs, as it does in commercial equipment driving.
1) Prolonged Sitting:
Prolonged sitting
causes many spinal vulnerabilities. Ligaments in the back help to hold the
spine together as one moves. These ligaments will stretch and slacken if a
person is sitting down for a long time while driving (Konz et al 1998). After
standing up, the ligaments remain slack
for a while, and cannot support the spine as they normally do.If the seat is
not adjusted correctly, pressure points can be developed in the buttocks and
back of the thighs, causing muscle strain in the lower back. If there is
vibration during this period, upper back and neck muscles of drivers are required to hold the head in
position, thereby causing continuous muscle activities, which can then lead to muscle strain.
Holding the foot over the pedal continually and over an extended period , may
also cause stiffness and spasms in the legs and lower back (Konz et al
1998).Maintenance of the same posture over a long period with continued muscle
tension becomes uncomfortable , and can
cause health problems.When sitting, the curve of the spine changes and pressure
is applied in different parts of the spine. Prolonged sitting intensifies that
pressure, leading to back problems, especially for drivers.
Additionally, the
driver must maintain a vigilant watch for traffic all the time, which requires
a fairly static head and neck posture. To maintain this steady driving posture,
internally the back, neck, shoulder and arm muscles maintain a static muscle
tension over a prolonged period of time. A steady low level muscle contraction
can lead to localized muscle fatigue (Konz et al 1998), which produces muscle
pains and fatigue.
·
Physiology of Muscle Fatigue and Pain
When the oxygen supply is inadequate, the cell can supplement energy
production through an anaerobic pathway, which metabolizes the nutrient
molecules to an intermediate stage. Thus the anaerobic metabolic process
produces less energy per nutrient
molecule , intermediate molecules produce lactic acid, which when
accumulated to a certain level of concentration, produces a localized sensation
of muscle pain, known as localized muscle fatigue. (Sjogaard et al. 1986) Blood
acts as a medium for carrying in and out oxygen, nutrients, and metabolic waste
products from the muscle cells, which are perfused with blood from the nearby
capillaries. During muscle contraction, a force develops within the muscle
tissue that increases intramuscular pressure. When the intramuscular pressure
is more than the capillary closing pressure (>30 mm Hg), the blood flow in
the nearby capillaries stops. It has been shown, that the blood flow
restriction starts at as low as at 10% and is completely restricted at a 50%
level of a muscle's maximum force capacity (Sjogaard et al. 1986). Restriction
of blood flow gives rise to anaerobic metabolism and increases the
concentration of lactic acid. The extent of muscle ischemia (lack of oxygen)
and concentration level of lactic acid accumulation depends on the type of
muscle work (dynamic or static) and the force level of muscle contraction. In a
dynamic type of muscular work, muscle contraction is interspaced by muscle
relaxation & during the muscle relaxation phase, intramuscular pressure
diminishes and blood flow to the muscle is re-established and replenishes the
oxygen stored in the muscles, and then carries away the metabolite waste
products. Static muscular work requires muscle tension to be maintained
continuously, without intermittent muscle relaxation. This type of muscle
contraction is mostly involved to counter the gravitational forces that are
acting on body segments. For example, when a driver is constantly watching the
road, the neck muscles are constantly acting to hold the head (average weight
14 pounds) in a fixed position. To maintain a driver's fixed driving posture,
muscles at the shoulder, neck, back, and the lower extremities, are at a
continuous contractile state for a prolonged period of time. Chaffin et al., 2006 predicted that muscles
can maintain sustained or static tension indefinitely when the level of tension
is below 15% of the muscle's maximum force generation capacity. Chaffin et al., concluded that even at less
than 5 percent of muscle’s maximum force generating capacity, muscle fatigue
and pain can develop if the tension is sustained for a prolonged period of time
(between 1000 and 10000 seconds).Ischemia due to static contraction and
accumulation of lactic acid is hypothesized to bring localized muscle fatigue.
While the fatigued cells are not themselves permanently damaged, reperfusion
after ischemia in muscle cells lead to micro-vascular and cellular
dysfunctions, initiating longer-term symptoms and functional changes in
skeletal muscle (National Research Council and Institute of Medicine, 2001).
Static contractions at low level over a prolonged period of time can cause
muscle to atrophy, splitting, necrosis and other degeneration, which in turn
precipitate as chronic muscle pain and discomfort, even when the static muscle
forces are not present.
2.) Whole Body
Vibration
In the human body,
vibrations are produced by either regular or irregular periodic movements of a
tool or vehicle, or other mechanisms that come in contact with a human and
which displace the body from its resting position.
The effects of
vibration and physical shock on human beings have been known for a long time,
example vascular disorders in fingers involving some impairment of circulation
and blanching of fingers , raynauld's phenomenon, traumatic vasospastic disease
(TVD), white finger (WF), or most commonly, vibration-induced white finger
(VWF).
Many professions have
been identified as "high risk" occupations, among them operators
of pneumatic, electrical, and diesel
hand tools, drivers of trucks, buses, cars and heavy equipment. One of the most
striking differences between automotive seats and other types of seats is their
dynamic environment. Vibration is transferred to a passenger at all points of
contact between the passenger and the vehicle. Therefore, vibration has been
considered as one of the major factors affecting passenger comfort (Oborne
1978; Griffin 1978). When vibrations are attenuated in the body, the vibration
energy is absorbed by tissue and organs. Vibrations lead to both voluntary and
involuntary muscle contraction and can cause local muscle fatigue especially at
resonant frequencies. Vertical vibrations in the 5-10 Hz range generally cause
resonance in the thoracic-abdominal system (at 4-8 Hz in the spine, at 20-30 Hz
in the head-neck-shoulder, and at 60-90 Hz in the eyeball (Chffin and Andersson
1984). There are many studies which suggest there is a risk of low-back pain
due to the effect of vibration (Rosegger and Rosegger 1960; Kelsey and Hardy
1975; Troup 1978). The principal
vibrations and frequencies which affect ride comfort are the seat cushion
vertical vibration (4-8 Hz), the seat-back lateral
vibration (8-16 Hz), and the foot vertical vibration (8-16 Hz) (Kzawa 1986).
Types of Vibrations :
Vibration can be
divided into the following types:
·
Harmonic and Periodic Vibration,
·
Random Vibration, and
·
Transient Vibration.
Vibration that is
comprised of one or several sinusoidal components is called harmonic or periodic vibration, and repeats itself
over time. One type of periodic vibration is that caused by out of balance
tires on a road vehicle. (Benstowe
et al., 2008)
Vibration that does
not repeat itself continuously is called random vibration. This type
of vibration is what one experiences
when driving a car on a bumpy road.
Vibration that is of a
short duration and is caused by mechanical shock is called transient vibration. Transient vibration occurs
when a vehicle hits a pothole.
Whole body vibration
is injurious to the body, regardless of the type of vibration. Whole body vibration
is generated by a system that accelerates the body in a motion.Three points at
which vibration enters the body are significant ergonomically: the buttocks,
the feet (when driving or riding in a vehicle), and the hands (when operating
hand tools, steering wheels, and machines) (Benstowe et al., 2008).
The direction of
oscillation is important. For the main part of the body, especially the
trunk/torso region, the direction of oscillation mostly lays in the vertical
plane (head to foot). For the hand and arm, the direction of oscillation is
often approximately perpendicular to the line through the hand and arm. (Benstowe et al., 2008)
The extent of the
biomechanical effects of vibration is strongly dependent upon the frequency
with which such effects are experienced. Studies have shown that the natural
frequencies are different in different parts of the body. (Benstowe et al., 2008) Particularly
important frequencies are those which fall into the range of natural
frequencies of the body and cause resonance. Since the natural frequency for
the human trunk falls in the range of 4-8 Hz, it is expected that the
whole-body vibrations that will most largely affect passengers will occur in
this frequency range (Ofori-Boetang, A. B. 2003).
The effect of vibrations
depends greatly on the duration, larger the duration more it will affect the
body. When we are standing up, any vertical vibrations transmitted at the feet
are quickly dampened in the legs. Vibration is dangerous, and as such,
different systems of the body attempt to absorb some of the shock to reduce
deleterious effects on a single organ or system (Benstowe et al., 2008). The distributive impact of the vibration,
then, may affect the whole body, as opposed to just the zone that would
otherwise be targeted if the rest of the body did not play this absorptive
function. Above the frequency of 2 Hz, the human body does not vibrate as a
single mass with one natural frequency; rather, it reacts to induced vibration
as a set of linked masses(Benstowe et
al., 2008).
Vibration experienced at
work has been measured mainly among employees who work with construction
machinery, tractors, trucks, and car drivers. The studies on various motor
vehicle operators have revealed that the acceleration of vertical oscillations
lies between 0.5 and 5m/s². Bumps on the road cause up-and-down vibration of
the vehicle or truck frame along the length of the spine hence inducing a
vertical vibration. The magnitude is how powerful the vibration is. The long
driving time of drivers is an indication of long exposure to whole body
vibration. (Benstowe et al., 2008).The
manner in which health is affected by oscillatory motions hence depends upon
the frequency, direction, and duration of motion, which is currently assumed
to be the same as, or similar to, that
for vibration discomfort.
·
Whole Body Vibration Effects on the Health of Drivers
The health effects of
whole body vibration vary considerably. Other factors such as ergonomic design,
damping, and resonance have a great effect on the exposure characteristics and
intensity levels of vibration exposure experienced by drivers. The main problem
is caused by the vibration energy waves, much the same as noise, which are
transferred from the energy source, such as the vehicle, onto the body of the
exposed driver and then transmitted through the body tissues, organs, and
systems causing various effects on the structures within the body before the
vibration is dampened and dissipates. The risk of illness depends on the
characteristics of vibration, namely magnitude, frequency, duration, and
direction. (Benstowe et al., 2008)
The period the drivers sits behind the driving
wheel, is a reasonable time of exposure to whole body vibration. This vibration
has many more widespread and varied effects; though the effects may not be felt
by the individual, but they are registered and
recorded by the body. Bovenzi (1992) linked low back pain to Whole Body
Vibrations (WBV) in his study of low back pain and exposure to WBV in
automobile drivers. The result of that study indicated that professional
drivers were at a greater risk of developing low back pain, which is caused by
various mechanisms of vibration on the musculoskeletal system of the body,
namely the degeneration of the inter vertebral discs, which leads to an
impairment of the mechanics of the vertebral column, thereby allowing tissues
and nerves to be strained and pinched.
(Benstowe et al., 2008) The nutrition of the discs is also affected by
long periods of sitting aggravated by vibration exposure, which causes tissue
nutrients needed for growth and repair of the discs to flow out of the discs by
diffusion instead of inwards where they are required. This leads to increased
wear and reduced repair of the discs. The vertebral bodies are also damaged by
the vibration energy that leads to an accumulation of micro fractures at the
end plates of the vertebral bodies and associated pain. Muscle fatigue also
occurs as the muscles try to react to the vibration energy to maintain balance
and protect and support the spinal column, but these are often too slow as the
muscular and nervous systems cannot react fast enough to the vibration shocks
and loads being applied to the body. Whole-body vibration causes a passive
artificial motion of the human body, a condition that is fundamentally
different from the self induced vibration caused by locomotion. (Benstowe et al., 2008)
Other health effects
that have been associated with whole-body vibration, and especially the driving
environment, are hemorrhage, high blood pressure, kidney disorders and
impotence. A literature review by Thalheimer (1996) indicated exposure to whole
body vibration may affect the cardiovascular, cardiopulmonary, metabolic,
endocrinologic, nervous and gastrointestinal systems of the body.
3.) Pressure Distibution & Haemodynamics
A seat cushion should
ideally distribute body weight properly, and should absorb shock and vibration. As Dempsey (1963) has pointed out,
75% of body weight is supported by the
buttock and especially high pressure is concentrated on 25 sq. cm of the
ischial tuberosity and the underlying
flesh. Dnunmond et al. (1982) showed that 18% of body weight is distributed
over each ischial tuberosity. This load is sufficient to reduce the blood
circulation through capillaries, and results in sensations of ache, numbness,
and pain (Chow and Ode11 1978; Bader et al. 1986). Therefore, the pressure
distribution between body and seat surface has been considered as one of the
most important factors affecting seating comfort (Their 1963; Hertzberg 1972; Kohara and Sugi 1972;
Kamijo et al. 1982; Diebschlag and Mueller-Limmroth 1980; Diebschlag et al.
1988). Also, a recent roadside survey (Schneider and Ricci 1989) suggests that pressure under the
buttock is the second largest source of driver seating discomfort (lumbar
discomfort is the largest source). Pressure exerted over a long period of time
can cause mechanical damage in tissues and cut off blood supply to the tissue.
Localized pressure can cause deformation, mechanical damage, and blockage of
blood vessels because soft body tissues are very deformable but are nearly
incompressible (Chow WW et al.,1978) Body tissue can tolerate 1655 kPa (240
psi, 12.4 m Hg, 500 feet deep under water) of hydrostatic pressures with no
difficulty. Whereas, a uniaxial pressure of less than 6.7 kPa (1 psi or 50 mm
Hg) will induce pathological changes in body tissue. (Chow WW et al.,1978)
The stress observed in
the buttock can be decomposed into a combination of shear stress and
hydrostatic stress. Hydrostatic pressure is relatively harmless to biological
tissues. Shear stress is more important and may impair the integrity of
capillary structure.Body tissue is more susceptible to shear forces than to
equivalent normal forces. Tangential forces of 6.7 kPa or 1.33 N/mm are
sufficient to induce pathological changes in body tissue. Chow and Ode11 (1978)
showed the shear pressure development inside the buttock due to surface
friction using a finite element model.
·
Haemodynamics
Extended periods of
sitting (Pottier et al. 1969; Glassford 1977; Winkel 1981, 1986) and prolonged
driving postures can decrease the lower body hemodynamics. This kind of discomfort is described as numbness, burning
feet, swollen feet and legs, and leg cramps. Hemodynarnic shift from the
central venous pool to the peripheral pool can cause drowsiness, dizziness, and
mental fatigue. Foot swelling was also observed. Pottier et al. reported 2.8%
of foot swelling after 2 hours of normal sitting. Also, an increase in
temperature accelerated foot swelling.
Winkel et al., 1986 also found similar results.
4.) Other factors
a.) Poor posture:
·
Personal habit
·
Improper adjusted or fitted seat
b.) Anthropometric
factors
·
Gender
·
Age
·
Stature
·
Weight
·
Sitting height
·
Limb length
c.) Psychological
factors:
·
Driving task workload
·
Side task workload
·
Training/familiarity
·
Exogenous stressors
d.) Vehicle layout:
·
Seat height
·
Seat track angle
·
Vision restriction
·
Headroom restriction
·
Steering wheel position , diameter & angle
·
Pedal control locations
·
Display locations
·
Mirror locations
·
Seatbelt locations
e.) Road conditions.
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