KNR 342
Occupational Biomechanics
Dr. Steve McCaw
227B Horton
438-3804
smccaw@ilstu.edu
www.cast.ilstu.edu/mccaw
Ergonomics
Ergo: work & nomos: natural laws
• Management & labor
recognize that injury
and reduced
performance reflect
a mismatch between
• the worker
• Job demands
• the task
• the environment.
Hierarchical Goals of
Occupational Biomechanics
Generate
• “tolerable”
• “acceptable”
• “optimal”
working conditions
Factors Affecting
Performance & Injury
Individual
People
are
different.
body size & shape (anthropometrics)
Performance & Injury
Individual
body size & shape (anthropometrics)
fitness level / injury history
Performance & Injury
Individual
body size & shape (anthropometrics)
fitness level / injury history
off-work activities
Performance & Injury
Individual
body size & shape (anthropometrics)
fitness level / injury history
off-work activities
psychological status
Psychology of Recovery
Use it to
your
advantage
Performance & Injury
Individual
body size & shape (anthropometrics)
fitness level / injury history
off-work activities
psychological status
Motivation: injury benefits
$$
social
Dilbert, by Scott Adams.
Performance & Injury
Environment
physical layout
Materials, tools, workstation
Work/rest cycles
psychological demands
The effect of stress to adverse health may be analogous to that of cigarette
smoking to lung cancer. While most people who smoke do not get lung
cancer, most cases of lung cancer are related to smoking.
Kroemer, Kroemer & Kroemer-Elbert, 2001.
Performance & Injury
Environment
Lighting, visual aids
Noise
?
From The Complexities of Cold
By Ronnie Rittenberry · February 1, 2008
http://www.ohsonline.com/articles/57758/
Example: Working in the Cold
• "I can go out and lift a box every day of my life, but
then if one day I lift it with four inches of heavy, wet
snow on it? It's not the same. And meanwhile I'm
wearing protective equipment that decreases the
efficiency of my lever systems? And I'm a little bit
discombobulated because I'm in a hurry, trying to get
out of the cold? This isn't the same box anymore.
There's a whole different gorilla sitting inside that box.
So I think that's what you look for, is that cold has
these multiple effects. It's a risk factor with many
variables."
•
•
From The Complexities of Cold
By Ronnie Rittenberry · February 1, 2008
•
http://www.ohsonline.com/articles/57758/
Performance & Injury
Task
KAZIMIR MALEVICH
Female reaper 1912
The Kustodiev Picture Gallery,
Astrakhan
At-risk occupations
U.S. Bureau of Labor Statistics, 1996
1. Truck driver.
2. Non-construction laborer.
3. Nursing aides and orderlies.
4. Janitors and cleaners.
5. Assemblers.
6. Construction laborers.
7. Carpenters
8. Stock handlers and baggers.
9. Cashiers
10. Cooks
11. Miscellaneous food preparation staff.
Illinois, 1999
Top 10
causes
of injury
Illinois, 1999
Performance & Injury
Task
KAZIMIR MALEVICH
Female reaper 1912
The Kustodiev Picture Gallery,
Astrakhan
Speed of working
Complexity of task
Fit of components
Performance & Injury
Individual
Environment
Task
Mismatch predisposes to Injury
Nothing is static.
Simple
model of
accident
causation.
Oborne, 1982.
Ergonomics
• Psychologists investigate mental
function and the workplace
• human factors, cognitive factors
• Exercise physiologists evaluate
metabolic, respiratory & CV effects of
prolonged, strenuous activities in
industry
• work physiology
Occupational Biomechanics
• Biomechanics
• apply laws of physics and engineering concepts to
• Describe motion undergone by various body segments
• kinematics
• Understand the forces acting on these segments
• kinetics
Biomechanics
Science concerned with
the mechanical behavior of
the NMS system and component tissues
when physical tasks are performed
Who Uses Occupational
Do.
Biomechanics? YOU Will.
• Engineers
• Workplace design
• Process control
• Safety Managers
• Allied health providers
• Physicians
• Nurses
• Rehabilitation personnel
• PT, OT, AT
Techniques of Biomechanics
• Kinematics - time and space variables.
• Displacement
• Velocity
• Acceleration
• Kinetics - force and energy variables
• F=ma
• Ft = mVf - mVi
• Fd = 1/2 mV2 + mgh
Biomechanics Techniques
• Kinematics - time and space
• Displacement
• Velocity
• Acceleration
• Kinetics - force (torque) & energy
• F=ma
• Ft = mVf - mVi
• Fd = 1/2 mV2 + mgh
Demands of the Task & Environment
Occupational Biomechanics
• complements psychological
and physiological
knowledge
• Considers physical
interaction of worker, task &
workplace
• Basis of OSHA guidelines
• Focus is mechanical stress
on the body
Occupational Biomechanics
• complements psychological
and physiological
knowledge
• Considers physical
interaction of worker, task &
workplace
• Basis of OSHA guidelines
• Focus is mechanical stress
on the body
Force / Area
Six Methodological Areas
Kinesiological
(Biomechanics)
Methods
Biomechanical
Modelling
Methods
Anthropometric
Methods
Mechanical Work
Capacity
Evaluation
Methods
Bioinstrumentation
Methods
Classification
and Time
Prediction
Methods
Seating
Design
Guidelines
Material
Handling
Limits
Occupational
Biomechanics
Personnel
Selection Criteria
and Training
Hand Tool
Design
Guidelines
Workplace and
Machine Control
Layout
Guidelines
Improved Performance
and Reduced Risk
of Mechanical Trauma
Major Application Areas
Objectives of Occupational
Biomechanics
Maximize safety & productivity
• Minimize fatigue &
overexertion
• Improve quality and
quantity of output
• Minimize time lost to and
cost of injury & accident
• Minimize absenteeism
and labor force turnover
Fit the Job to the Worker.
Tools, layout, organization, flow
Need for Biomechanics Evaluation:
• increased complexity of industrial and
manufacturing processes
• rising costs
• health care, rehabilitation, insurance
• increase in litigation / bad PR stemming
from injury
• new legislation (anticipated??)
• OSHA 2000 rejected 2001
Knowledge of Occupational
Biomechanics is used to:
• Evaluate physical demands of existing
jobs and workplaces
• Suggest alternative work methods
• scientific principle/basis for change
• Facilitate employee selection and
placement procedures
Social/legal support for
occupational biomechanics
• Hiring cannot discriminate on basis of
•
•
•
•
age
race
gender
disability
• but jobs must not provide undue risk for
injury
OSHA Act of 1970
Employers are to provide employees with:
• Competent fellow employees & managers
• A safe working environment
• Knowledge of hazards
• Safety rules
• Safe tools
Implementing a Program
Attitude
Employee
- Self-help
Employer
- Investment
Safety must be accepted as:
• Legally necessary
• Economically advantageous
• Ethically imperative
Need for an
Occupational Biomechanics Specialty
Epidemiological support of occupational
biomechanics
• Health and quality of life are greatly
reduced for many because of
musculoskeletal disorders
• acute
• chronic
We want to encourage employers
to take the high road to safety
- Joseph A. Dear
Former OSHA Administrator
We want to encourage employers
to take the high road to safety and
we will use our enforcement
program to preclude them
from taking the low road.
- Joseph A. Dear
Former OSHA Administrator
Dealing
with injury
creates a
logistical
nightmare
The Need for an Occupational
Biomechanics Specialty
• 1990
• 1.8 million disabling work injuries in US
• permanent impairment: 600,000
• 72% of injuries of 3 kinds
• overexertion (31%)
• collision (struck by or striking) (24%)
• falls (17%)
Event: Sudden Force
• Trauma Type: Impact
• Typical Medical Outcomes:
•
•
•
•
•
•
Contusion (bruise)
Laceration (cuts)
Sprain (ligament)
Fracture (bone)
Subluxation \ dislocation (joint)
Concussion (brain)
Event: Repeated Motion
• Trauma Type : Overexertion, overuse injury
• RMI: repetitive motion injury
• RSI: repetitive strain injury
• CTD: cumulative trauma disease
• RMD: Repetitive Motion Disorder
• OOD: Occupational Overuse Disorder
• UECTD: Upper Extremity Cumulative Trauma
Disorder
• Vibration syndrome
Event: Volitional Activity
• Trauma Type: Overexertion
• Typical Medical Outcomes
•
•
•
•
•
Muscle strain
Tendonitis: inflamed tendon
Tenosynovitis: inflamed tendon sheath
Myofascial Disorders
Nerve Entrapment Disorders
• Low Back Pain
• Carpal Tunnel Syndrome
Types of Injuries
(Bureau of Labor Statistics, 1999)
739.7
Sprain&Strain
156
132.4
113.7
Contusions
Lacerations
Fractures
Burn/Scald
CTS
Tendonitis
ChemBurns
Amputations
27.1
27.9
16.6
11.6
10
Values * 1000
At-risk occupations
U.S. Bureau of Labor Statistics, 19961999
3. Nursing aides and orderlies.
1. Truck driver.
2. Non-construction laborer.
5. Assemblers.
4. Janitors and cleaners.
Registered Nurses
8. Stock handlers and baggers.
6. Construction laborers.
9. Cashiers
Sales Supervisors and proprietors
7. Carpenters
10. Cooks
11. Miscellaneous food preparation staff.
Illinois, 1999
Job-related Injuries
• Bureau of Labor Statistics (for 1994)
• 705,000 (32%) of illness causing missed work
were overexertion \ repeated motion
• 367,000(52%) were lifting related
• 65% affected the back
• median 6 days off work (mean = 120 days) Interpret?
• 93,000 (13%) were pushing/pulling related
• 52% affected the back
• median 7 days off work
• 69,000 (10%) holding, carrying, turning objects
• 58% affected the back
• median 6 days off work
Cost of overuse/overexertion
injuries to society (1995)
•
•
•
•
lost wages
lost productivity
administrative expenses
health care costs
Cost of overuse/overexertion
injuries to society (1995)
• Depends who you talk to
•
•
•
•
Textbook (no source): $126 billion
National Safety Council: $119.4 billion
NIOSH: $13-20 billion
California Worker’s Compensation Board
• $21,453 average cost
• National Council on Compensation
Insurance
• $12,370 average RMI claim
Cost of overuse/overexertion
injuries to society (1995)
• Depends who you talk to
• National Safety Council: $119.4 billion
• NIOSH: $13-20 billion
• California Worker’s Compensation Board
• $21,453 average cost
• National Council on Compensation
Insurance
• $12,370 average RMI claim
Regardless of the estimate used, the problem is large
both in health and economic terms.
Injured Worker Characteristics
• Men
• 66% of injury (55% of workforce)
• Age
• 25-44: 57% of injury (54% of workforce)
• >45 years: 24% of injury (29% of workforce)
• Most workers > 1 year service
• 25% injured > 5 years service
Forerunners of Overuse
Disorders
•
•
•
•
•
Rapid and often-repeated actions
Exertion of finger, hand, or arm forces
Pounding and jerking
Contorted body joints
Polished-by-use sections of the workplace or
clothing; custom-made padding
• Blurred outlines of the body owing to vibration
• The feeling of cold and the hissing sound of
fast-flowing air
K, K & K-E, 2001
Injury, Acclimatization, &
Chronic Injury
Stress & Tolerance
1-10 weeks to injury
Time
Stress & Tolerance
Injury, Acclimatization, &
Chronic Injury
1-2 weeks
Time
Illinois, 1999
Assumption: days off is
related to injury severity.
Placebo effects and surgery for
treatment of overuse injuries.
Biomech-L
June 22, 2006
Research has shown that arthroscopic debridement operations on the knee for
osteoarthritis often provide little more than a placebo effect. Many patients
report symptomatic relief after undergoing arthroscopy of the knee but it is not
clear how the procedure achieves this result. A randomized controlled trial to
evaluate the efficacy of arthroscopy for osteoarthritis of the knee showed that
the outcomes after arthroscopic lavage or arthroscopic debridement were no
better than those after a placebo procedure (Moseley et al, 2002).
Does anyone know if anyone has done any similar research concerning
common surgical treatments for overuse injuries? Hutson (1997) has cast
doubt on the efficacy of many forms of medical treatment for overuse injuries
(such as splinting a sore wrist rather than resting it); hence it would be
interesting to know if the outcomes of surgery for carpal tunnel syndrome (i.e.
decompression of the carpal tunnel) ever reflect a placebo effect (especially if
this is merely due to rest after the operation).
Regards,
David McFarlane, Ergonomist, WorkCover Authority, New South Wales, Australia
References
1. J. Moseley, K. O'Malley, N. Petersen, T. Menke, B. Brody, D. Kuykendall, J. Hollingsworth, C. Ashton and N. Wray, (2002), "A Controlled Trial of
Arthroscopic Surgery for Osteoarthritis of the Knee", New England Journal of Medicine, July 11, 2002, Volume 347:81-88, Number 2.
2. M. Hutson, (1997), "Work-Related Upper Limb Disorders: Recognition and Management", (Butterworth-Heinemann; Oxford).
Stress & Tolerance
Injury, Acclimatization, &
Chronic Injury
2-8 weeks
Time
Cost of overuse/overexertion
injuries to society (1995)
Pantagraph, 7/18/06
Stress & Tolerance
Injury, Acclimatization, &
Chronic Injury
Up to 20 years
Time
Simple
interventions
can be VERY
effective.
12 principles of
ergonomics
Don’t call it Fitness
Working Pain-Free
By Jon Siegel ·
Occupational Safety & Health, January 2008
Kimberly-Clark Employee
Maintenance Centers help to
reduce incident rates at
manufacturing plants, which
boosts productivity and the
bottom line.
Read the article on-line: what is this all about??
Goal: understand biomechanics
of “awkward posture”
LIFTING A LEVER
Thanks to
Richard Hughes
U Michigan, for the
following slides.
MECHANICS OF LEVER
3F = 30FHAND
F=
FHAND
30
3
FHAND
F = 10 FHAND
F
MECHANICAL ANALYSIS
FHAND
F
NEWTON’S THIRD LAW
FHAND
FHAND
MECHANICS OF SPINE
2FMUSCLE = 12FHAND
12
FMUSCLE =
2
FHAND
FMUSCLE = 6 FHAND
FHAND
FMUSCLE
Low back pain and Lifting
Study: Training Won't Prevent Back Injuries
February 2, 2008
Training showing the correct way to lift heavy objects does not prevent back injuries, according to a systematic review published on
the Web site of the BMJ (British Medical Journal).
Back pain is a highly prevalent complaint and a cause of much suffering. In the UK, employers have to ensure workers get proper
training on how to handle loads correctly and this generally includes advising workers on specific lifting techniques. However this
study, which reviewed all the evidence currently available, found no evidence that the advice has any effect.
The researchers looked at 11 studies: eight studies dealt with health workers who manually handled patients, the other three looked
at baggage handlers and postal workers. All the participants in the studies worked in jobs where there was strain on the back and
where there was the potential for alleviating any strain through an intervention such as training. None of the workers in the studies
were actively seeking treatment for back pain.
The researchers found no difference in back pain in studies where one group received training and the other didn’t. Training
compared to minor advice (a video) showed no effect on back pain after a year.
Another trial showed no significant difference in back pain between one group who received training and another who were given
back belts to wear. Training and physical exercise were compared in one trial and again no difference in back pain was found
during a follow up less than a year later.
Finally a group receiving both training and an assistive device was compared to a group receiving training only and another control
group which received nothing -- there was no difference in back pain at follow up.
The researchers say either the advocated techniques do not actually reduce the risk of back injury, or workers do not significantly
change their habits enough for it to make any difference.
They concluded that what's needed is a better understanding of the relationship between exposure to stresses on the back at work
and the subsequent development of back pain in order to develop new and innovative ways of preventing back pain because of
lifting.
In an accompanying editorial, Associate Professor Niels Wedderkopp says the current advice for people with back pain to stay
active may not be appropriate for people whose work involves heavy lifting. He stated: "A change of job and (prudently) staying
active in daily life may be the best way for these patients to regain command of their back and their occupation."
http://www.ohsonline.com/articles/58040
Occupational Risk Factors: FIT
(Cumulative Trauma Disorders)
• Mechanical Stress (Force / area)
• Frequency (Repetition)
• Intensity (Force exerted)
• Time (Duration of loading)
Next : the BIO portion
• Osteology
• study of bones.
• Arthrology
• study of joints.
• Myology
• study of muscles.
• Neurology
• study of nerves.
Call it a night.