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EHS 218 Occupational Ergonomics. Risk Factors and Musculoskeletal Disorders. Risk Factor. Risk is the probability or likelihood of injury. A risk factor is any element that contributes to this probability. Personal Risk Factors for Musculoskeletal Disorders. Rheumatoid Arthritis

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Ehs 218 occupational ergonomics

EHS 218 Occupational Ergonomics

Risk Factors and Musculoskeletal Disorders

Risk factor
Risk Factor

  • Risk is the probability or likelihood of injury.

  • A risk factor is any element that contributes to this probability.

Personal risk factors for musculoskeletal disorders
Personal Risk Factors for Musculoskeletal Disorders

  • Rheumatoid Arthritis

  • Endocrinological Disorders

  • Acute Trauma (such as burns, lacerations)

  • Vitamin B6 Deficiency

  • Wrist size and shape

  • Obesity

Personal risk factors for musculoskeletal disorders1
Personal Risk Factors for Musculoskeletal Disorders

  • Gender and Age

  • Pregnancy

  • Oral Contraceptives

  • Gynecological Surgery

  • Fitness Level

  • Certain Medications

Ergonomic risk factors for musculoskeletal disorders
Ergonomic Risk Factors for Musculoskeletal Disorders

  • Repetition

  • Awkward posture

  • Force

  • Vibration

  • Contact pressure

  • Cold temperatures


  • Refers to how frequently a task or set of motions is performed

  • Involves rapid and frequent muscle contractions which subject joints/muscles to high stress without adequate time for recovery

Awkward posture
Awkward Posture

  • Refers to taking the body out of its normal alignment or moving a joint toward the end ranges of motion.


  • Refers to muscle force exerted by the body and outside forces exerted on the body

  • Causes deformation of tissues


  • Transmitted to the body via the hand or entire body

  • It affects the blood vessels, intervertebral disks, and low back

  • Results in impaired circulation which in turn affects muscle function

Contact pressure
Contact Pressure

  • Produced when soft tissues are squeezed between bone and external objects such as tools, parts, or equipment

Cold temperatures
Cold Temperatures

  • Results in circulatory, sensory, and motor impairments that affect manual dexterity and nerve function

Musculoskeletal disorders1
Musculoskeletal Disorders

  • Tendon disorders

  • Nerve disorders

  • Neurovascular disorders

  • Muscular injuries

Tendon disorders

Tendon Disorders

Tendinitis, Tenosynovitis, DeQuervain’s Tenosynotitis, Trigger Finger, Epicondylitis


  • Inflamation of a tendon

  • Occurs when a muscle/tendon unit is repeatedly contracted

  • With excessive exertion, some tendon fibers can tear

  • Tendon can become thickened, bumpy and irregular or calcified

  • Without rest, the tendon can be permanently weakened


  • A tendon injury involving the synovial sheath

  • Excessive synovial fluid is produced, and the sheath becomes swollen and painful

Dequervain s tenosynovitis
DeQuervain’s Tenosynovitis

  • A special case of stenosing tenosynovitis

  • Stenosis is a progressive constriction of the tendon sheath

Dequervain s tenosynovitis1
DeQuervain’s Tenosynovitis

  • Involves the 2 tendons that abduct and extend the thumb

  • They run through a common sheath at the side of the wrist

  • Attributed to repetitive friction b/w these tendons

  • Clothes-wringing motion

Trigger finger tenosynovitis
Trigger Finger (Tenosynovitis)

  • When the tendon sheath becomes sufficiently swollen

  • The tendon becomes locked inside the sheath

Trigger finger tenosynovitis1
Trigger Finger (Tenosynovitis)

  • Attempts to move finger cause a snapping/jerking movement

  • Associated with tools with hard or sharp edges

Ganglion cyst
Ganglion Cyst

  • The tendon sheath swells up with synovial fluid

  • Causes a bump under the skin

  • “Bible bumps”


  • Inflammation of the unsheathed tendons in the elbow joint

  • Due in part to the imbalance in the elbow between the large forearm muscles and their small insertion areas on the humerous (the epicondyles)

Medial epicondylitis golfer s elbow
Medial Epicondylitis (Golfer’s Elbow)

  • Involves the finger flexor tendons located on the medial elbow

  • When strained or overused, the tendons become irritated and radiate pain from the elbow down the anterior arm

  • Tasks that require repeated forceful rotation of the forearm and bending of the wrist

Lateral epicondylitis tennis pitcher s bowler s elbow
Lateral Epicondylitis (Tennis, Pitcher’s, Bowler’s Elbow)

  • Involves the finger extensor tendons located on the lateral elbow

  • When strained or overused, the tendons become irritated and radiate pain from the elbow down the posterior forearm

  • Using the arm for impact or jerky throwing motions

Shoulder impingement syndrome
Shoulder Impingement Syndrome

  • Recall that the shoulder is a complex joint

Shoulder impingement syndrome1
Shoulder Impingement Syndrome

  • Impingement is a rubbing or pinching action

  • Impingement occurs somewhat during everyday activities when using the arm above shoulder height

  • Working continuously overhead, repeated throwing, or other repetitive actions can cause impingement to be a problem

Shoulder impingement syndrome2
Shoulder Impingement Syndrome

  • Usually there’s adequate space between the acromion and rotator cuff for the tendons to slide easily as the arm is flexed

  • Some impingement on the tendons and the bursa is normal

Shoulder impingement syndrome3
Shoulder Impingement Syndrome

  • Impingement becomes a problem when it irritates or damages the rotator cuff tendons

  • It’s also related to irritation of the bursa caused by the humerous forced against the acromion

Shoulder impingement syndrome4
Shoulder Impingement Syndrome

  • In some people, the space between the acromion and rotator cuff is too small because the acromion is oddly sized

Nerve disorders

Nerve Disorders

Carpal Tunnel Syndrome (CTS)

Guynon’s Canal Syndrome

Radial Tunnel Syndrome

Cubital Tunnel Syndrome

Nerve disorders1
Nerve Disorders

  • Occur when repeated or sustained work expose the nerves to pressure from hard, sharp edges of work surface, tools, or nearby bones, ligaments and tendons

Carpal tunnel syndrome
Carpal Tunnel Syndrome

  • Tendons that flex the fingers, the median nerve, and blood vessels pass through the carpal tunnel

Carpal tunnel syndrome1
Carpal Tunnel Syndrome

  • The tendons, median nerve, and blood vessels are enclosed by the flexor retinaculum (carpal ligament)

Carpal tunnel syndrome2
Carpal Tunnel Syndrome

  • If any of the tendon sheaths become swollen in the carpal tunnel, the median nerve may be pinched

Carpal tunnel syndrome3
Carpal Tunnel Syndrome

  • Symptoms of CTS includes numbness, tingling, and pain in the thumb, first 2 fingers, and lateral side of the 3rd finger

  • Symptoms may be most severe while sleeping

Carpal tunnel syndrome4
Carpal Tunnel Syndrome

  • Advanced cases of CTS may cause weakness of the thenar muscles at the base of the thumb

Carpal tunnel syndrome5
Carpal Tunnel Syndrome

  • Nerve conduction velocity tests are sometimes used to help diagnose CTS

  • Carpal tunnel release surgery can relieve the pressure

Guyon s canal syndrome
Guyon’s Canal Syndrome

  • Compression of the ulnar nerve as it passes through the Guyon tunnel at the wrist

Guyon s canal syndrome1
Guyon’s Canal Syndrome

  • Guyon's canal is formed with the pisiform and hamate and the ligament that connects them. 

  • After passing through the canal, the ulnar nerve branches out to supply feeling to the little finger and half the ring finger. 

Guyon s canal syndrome2
Guyon’s Canal Syndrome

  • Overuse of the wrist, especially flexion and ulnar deviation

  • Placing constant pressure on the palm

  • Symptoms are pain, numbness, and tingling in the anterior side of the palm, last finger, and ½ of the ring finger

Radial tunnel syndrome
Radial Tunnel Syndrome

  • At the lateral elbow, the radial nerve travels in a tunnel formed by the surrounding muscles and bone

  • Runs below the supinator and down the posterior forearm

  • Difficult to diagnose; similar to lateral epicondylitis

Cubital tunnel syndrome
Cubital Tunnel Syndrome

  • The cubital tunnel is located on the medial elbow where the ulnar nerve passes

  • The ulnar nerve enervates the little finger and half the ring finger

Neurovascular disorders

Neurovascular Disorders

Thoracic Outlet Syndrome

Vibration Syndromes

Neurovascular disorders1
Neurovascular Disorders

  • Involve nerves and adjacent blood vessels

Thoracic outlet syndrome
Thoracic Outlet Syndrome

  • Compression of the nerves and blood vessels between the neck and shoulder

  • Abduction causes the brachial plexus to be stretched under the pectoralis muscle

Thoracic outlet syndrome1
Thoracic Outlet Syndrome

  • Result is that muscles, tendons and ligaments are deprived of oxygen and nutrition

  • Symptoms are numbness in the fingers and hand

  • Frequent reaching above shoulder level

Vibration syndromes
Vibration Syndromes

  • Hand-arm vibration (Raynaud’s Disease)

  • Whole-body vibration

Hand arm vibration raynaud s disease
Hand-Arm Vibration Raynaud’s Disease

  • Disorder of the small blood vessels in the skin

  • During an attack, arteries contract briefly, limiting blood flow (vasospasm)

  • When the skin is deprived of oxygen, it turns white and then blue

  • The skin turns red as the arteries relax and blood flows again

Hand arm vibration raynaud s disease1
Hand-Arm Vibration Raynaud’s Disease

  • Recurrent episodes can cause complete closure of the arteries

  • Exposure to cold or vibration may trigger vasospasm in the fingers

Vibration white finger or raynaud s disease
Vibration White Finger or Raynaud’s Disease

  • Forceful gripping and use of vibrating tools

  • Symptoms:

    • intermittent numbness and tingling of the fingers

    • skin that turns pale and cold

    • eventual loss of sensation and control in the fingers and hand

Whole body vibration
Whole Body Vibration

  • Vibration passing through the butt or feet

  • The most widely reported injury is back pain due to:

    • intervertebral disk degeneration

    • affect on nutrition to the disks

    • micro-fractures to the vertebral bodies

    • muscular fatigue

  • Also affects other body organs

Muscle injuries

Muscle Injuries

Low Back Pain (LBP)

Low back pain
Low Back Pain

  • Costs the US over 80 billion dollars each year

  • Eight out of ten people will have back pain at some time during their lives

  • Often occurs between the ages of 30 and 50

Low back pain1
Low Back Pain

  • Most episodes will resolve

  • In some cases, back pain becomes chronic

  • No quick fix or total cure for most back problems

  • Chronic back problems can be treated effectively to limit the impact on daily life

Low back pain2
Low Back Pain

  • Most low back pain doesn’t occur suddenly

  • Over many years the back is subjected to repeated stress which may not cause pain at the time the “injury” actually occurs

  • The repeated “injuries” can slowly cause degeneration of the spine and ultimately result in low back pain

Low back pain3
Low Back Pain

  • There may be an acute injury that causes pain, but the overall condition of the spine is also very important

  • Conditioning usually determines how fast one will recover, and the risk of the condition becoming chronic

Low back pain4
Low Back Pain

  • Causes of LBP include:

    • muscle strain

    • bulging or herniated disk

    • degenerative disk disease

    • spinal stenosis

    • sciatica or pinched nerve

    • sacroiliac joint inflammation

Intervertebral disk
Intervertebral Disk

  • The disk is subjected to many different stresses

  • The disk generally acts like a shock absorber

  • Trunk flexion results in compression of the disk

  • Repeated trunk flexion, over time, may cause the disk to bulge backwards towards the spinal canal and nerves

  • This is magnified when an external force is involved

  • Torso rotation and flexion together results in the greatest stress on the spine

Intervertebral disk1
Intervertebral Disk

  • A tear in the outer rings of the disk (annular ligament) allows the nucleus to squeeze into the spinal canal

  • If the nerve root is compressed by the disk material, there is pain, numbness, and weakness in the areas supplied by the nerve

Intervertebral disk2
Intervertebral Disk

  • In severe cases, the disk material can fill the entire canal

  • This causes paralysis of some muscles

Intervertebral disk3
Intervertebral Disk

  • Example of disk degeneration – the disk loses its ability to absorb shock

Intervertebral disk4
Intervertebral Disk

  • Example of a herniated disk

Control measures
Control Measures

  • Engineering controls

  • Work practice controls

  • Administrative controls

Engineering controls
Engineering Controls

  • Design or change physical aspects of the workplace to reduce or eliminate exposure to risk factors

Work practice controls
Work Practice Controls

  • Improve job content

  • Improve the processes workers use to accomplish their work

Administrative controls
Administrative Controls

  • Reduce duration of exposure

  • Slow the onset of fatigue

  • Increase worker’s ability to cope with stress

Strategies for repetition
Strategies for Repetition

  • Maintain tools

  • Efficient work methods to avoid unnecessary movements

  • Work with both hands

  • Limit overtime and extended work shifts

  • Job enlargement

  • Job rotation

  • Self-pacing design

  • Improve process quality to avoid rework

  • Micro-breaks

  • Avoid systems that discourage breaks

Strategies for awkward posture
Strategies for Awkward Posture

  • Position work items within convenient reach

  • Avoid extended reaching

  • Use reach envelope

  • Adjust workstation heights appropriately

  • Select tools which allow neutral postures

  • Avoid twisting postures

  • Avoid work above shoulder level or below hip level

  • Take breaks if working in static position

Strategies for force
Strategies for Force

  • Powered tools

  • Exert minimal amount of force

  • Use fixtures

  • Support or counterbalance tools > 2 lbs.

  • Don’t pound with palm of hand

  • Avoid large or thick gloves which make gripping difficult

  • Use carts, conveyors, lifts, hoists, etc.

Strategies for vibration
Strategies for Vibration

  • Keep machines/power tools well maintained

  • Choose low-vibration models

  • Use vibration-reducing or isolating mounts

  • Limit exposure to vibration

  • Job rotation

  • Job enlargement

  • Rest breaks

  • Use minimal force required

  • Use padding or coating

  • Gloves

  • Don’t lift heavy loads after driving for prolonged periods

Strategies for contact stress
Strategies for Contact Stress

  • Avoid tools that dig into palm or fingers

  • Use tape or cushioning

  • Round or pad sharp edges

  • Provide mats or footstools to relieve leg stress

Strategies for cold temperatures
Strategies for Cold Temperatures

  • Dress appropriately

  • Use layers depending on task performed

  • Limit exposure to cold

  • Allow breaks in warmer environment

  • Well fitted gloves

  • Avoid tight fitting items which reduce circulation

  • Be cautious about forceful exertion because stiff joints/muscles increase risk of injury