9.1 Types, causes and examples of musculoskeletal hazards

Question 1

Different joints allow different ranges of movement, as explained below, and also
shown in Figure 9.3.

Answer 1

(a) Gliding joints, between the ribs and thoracic vertebrae, for example, allow
bones to move or slide past each other.
(b) Hinge joints, such as the knee and elbow, allow movements which alter the
angle in one plane between two articulating bones.
(c) Pivot joints, such as the axis and atlas in the neck, allow rotation. The elbow is
also articulated between the radius and ulna to allow the lower arm to be
twisted.
(d) Ellipsoid joints, such as the wrist, are similar to ball and socket, but have less
movement.
(e) Saddle joints allow for back and forth or up and down movement, but no
rotation. The thumb is the only example of a saddle joint.
(f) Ball and socket joints, such as the hip, allow movement in all directions
(including rotation). This occurs as the ball-shaped end of one bone (the femur)
moves within a cup-shaped cavity of another (the pelvic girdle).

Question 2

First class levers have the fulcrum in the middle. The effort and resistance are 
applied at opposite ends. An example is

Answer 2

the movement of the skull on the spinal

column.

Question 3

Second class levers possess the fulcrum at one end and the resistance in the 
middle. The effort is applied at the other end. An example is

Answer 3

seen when raising

the body on the toes.

Question 4

Third class levers are the commonest type in the body. The fulcrum is at one
end of the lever and the resistance at the other end. The effort is applied to the
middle. An example is

Answer 4

the flexion of the forearm.

Question 5

Biomechanics applies the physical laws of mechanics to the human body, enabling
estimation of the local mechanical stress on muscles and joints arising from adopting
a posture or making a movement. Some important considerations are 8

Answer 5

Joints must be in
a neutral position

The work should
be kept close to
the body

Bending forward
should be
avoided

Twisting the
trunk should be
avoided

Peak stresses are
produced by
sudden
movements

Postures should
be varied, as well
as movements

The duration of
continuous
muscular effort
should be limited

Short frequent
breaks are better
than longer
infrequent breaks

Question 6

Physiological studies permit estimates to be made of the energy demands on the
heart and lungs resulting from muscular effort during movements, considering both
localised fatigue from continuous localized muscular effort and general body fatigue
from carrying out physical tasks over a prolonged period.

Important principles include: 2

Answer 6

Limiting the energy expenditure in a task

Resting after heavy tasks

Question 7

Anthropometry is the study of the size and proportions of the human body.
Anthropometric principles of importance to the ergonomics of posture and
movements include: 2

Answer 7

 Taking account of differences in body size when designing workstations,
workplaces and accessories etc.
 Using anthropometric tables that are appropriate for the specific population.

Question 8

The causes of WRULDs are not clear, but key risk factors are: 7

Answer 8

 repetitive work
 uncomfortable working postures
 sustained or excessive force
 carrying out a task for a long period of time
 poor working environment (example: temperature and lighting)
 poor work organisation (example: work pressure, job demands, work breaks or
lack of them)
 individual differences and susceptibility (some workers are more affected by
certain risks).

Question 9

Tendonitis

fingers/hand/forearm

Answer 9

Inflammation of the tendon.

Question 10

Tenosynovitis

Answer 10

Inflammation of the tenosynovium (tendon

sheath) and tendon.

Question 11

De Quervain’s

Answer 11

Tenosynovitis affecting thumb tendons.

Question 12

Trigger finger

Answer 12

A stenosing tenosynovitis, locking a finger in
either a bent or straight position
Note: Stenosing is the narrowing of the tendon
sheath.

Question 13

Carpal tunnel syndrome

Answer 13

Tendonitis or tenosynovitis of the tendon
passing through the carpal tunnel compresses
the median nerve, affecting sensation on the
palm side fingers and thumb.

Question 14

Shoulder capsulitis

frozen shoulder

Answer 14

Inflammation of the shoulder capsule, which is

the connective tissue around the shoulder joint.

Question 15

Epicondylitis

example: tennis elbow

Answer 15

Tendonitis affecting the elbow or knee

Note: a condyle is a knuckle joint.

Question 16

Cervical spondylosis

Answer 16

Degenerative osteoarthritis of the joints
between the centra of the spinal vertebrae in
the neck.
Note: the centra are the solid parts of a
vertebra

Question 17

Tension neck syndrome

Answer 17

Symptoms include: pain, tenderness and
stiffness of muscles, signs of hardened bands
or nodularities, and muscle spasm.

Question 18

WRULD Risk factors

Answer 18

Repeating an
action

Uncomfortable
working
positions

Using a lot of
force

Carrying out a
task for a long
period of time

Poor working
environment

Underlying
effects of the
work and
conditions

Workers’
individual
differences