Understanding and Preventing
Repetitive Stress Injuries
Brian Rouse MSPT, OCS
Goals
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Understanding normal body function
Identifying how position affects function
Guidelines for workspace assessment
Tips/exercises to improve body function
Defining Ergonomics
 Involves adapting a task to a person, not making
the person change for the task
 Altering the task, the environment, or both
http://www.wark.csiro.au/library/gifs/ergonomics.gif
Anatomic Efficiency
 Joints
– Two bones meet and move against each other
 Primary damage is from compression and friction
 Areas of joint loaded unevenly = faster damage
 Muscles
– Control joint movement, hold body in place
 Work to produce forces or stabilize against gravity
 If too much work is performed = muscle fails
 Focus of ergonomics is DOING LESS WORK
Fighting Gravity
http://www.posturepal.com/assets/images/sci2.jpg
Consequences of Poor Posture
 Cumulative Trauma/Repetitive Stress
– “Itis” means inflamed/overstressed
 Tendonitis, bursitis, synovitis, arthritis
 Tissues that work too hard will complain
 Permanent Body Changes
– Arthritis cartilage damage does not regenerate
– Disc degeneration does not reverse
– Nerve compression can block signals
 Carpal tunnel, pinched nerve, sciatica
Ergonomics Made Simple
 Use body positions requiring less work
– Muscles sustain less damage from overworking
 Use other objects to hold body in place
– A muscle at rest cannot be overworked
The Easy Way is the Best Way
Challenges in Ergonomics
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Designing for “Average”
Lack of variance in work tasks
Time constraints for job completion
Costs of modifying environment
http://solutions.3m.com/wps/portal/3M/en_US/ergonomics/home/advice/workspacecomfortguide/
Guidelines: Head/Neck
 Monitor positioned 20”-30” from eyes
– Use arms length as a guide
– Top of monitor should be at/slightly lower than
eye level
– Use document holders to read while typing
 Head should be centered over shoulders
– Use “turtle” method to draw head back
Shoulders/Arms
 Shoulders/upper arms perpendicular to floor
 Elbows close to sides/torso, at 90 degrees
 Forearms on armrests, allowing shoulders to
drop
 Do not rest on hard/sharp armrest edges
Keyboard
 Keyboard trays for height/proximity
 Wrist needs to be neutral, not bent back
– Wrist rests pad hard desktop, hold wrist up
 Use only when not typing or mousing
 “Float” hands over keyboard while typing
 Mouse next to keyboard, easy to reach
– Move mouse with elbow/forearm, not wrist
Chair Adjustment
 Chair height level
– Hips/trunk at 90 degree angle or slightly more
– Feet flat on floor
 Can use foot stool if needed
– Thighs should fit under desk
 Or keyboard tray if needed
 Seat pan should be 1-2” wider than hips on
either side
Chair Adjustment
 Backrest
– Position lumbar support in natural curve of back
 If insufficient, add towel roll/etc. behind curve
– Shoulder blades able to rest against chair back
– Should allow user to tilt back 15 degrees
Common Mistakes
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Head position too far forward
Monitor set at diagonal to worker
Forearms not on armrests
Shoulder blades off of backrest
Lumbar curve in chair not flush with back
Monitor set too low
Feet not flat on floor/stool
Considerations for Standing Tasks
 Alter height of workstation or user
 Have footrest to allow weight shift of legs
 Organize workstation to allow controls/tools
to be in close proximity
 Have a chair in proximity, using for tasks
that can be seated or just rests
 Use proper footwear and anti-fatigue mats
Standing Workstations
 Precision tasks (writing): 5 cm above elbow height
 Light tasks (assembly): 5-10 cm below elbow
height
 Heavy tasks (downward force): 20-40 cm below
elbow height
Canadian Centre for Occupational Health and Safety;
www.ccohs.ca.oshanswers/ergonomics/
Task Modification
http://www.uhs.berkeley.edu/facstaff/ergonomics/lab/tools.shtml
 20-20-20 rule
– 20 minutes of work
– 20 second rest (bare minimum)
– Look away from screen
 Adjust schedule as able to break up work
Desk Stretching
 Longer holds are better, try for up to 30 seconds
when possible
 Perform before/after work, during breaks
 Order does not matter, just frequency (1+ hours)
Warning Signs/Symptoms
 Pain--severe intensity or long duration (2-3 days)
 Changes in sensation
– Numbness, tingling, burning
 Unexplained weakness/fatigue
 Difficulty with coordination/clumsiness
 Abnormal swelling/redness
Other Considerations
 Strengthening postural muscles with
exercise (yoga, strength training, etc)
 Sleep and proper diet aid in prevention of
injury and healing
 Health problems (hypertension, diabetes)
can increase risk of injury development
Resources
 University of California—Los Angeles
http://ergonomics.ucla.edu/index.html
 University of California—San Diego
http://blink.ucsd.edu/Blink/External/Topics/Policy/0,1162,4008,00.html
 Canadian Centre for Occupational Health and Safety
http://ccohs.ca/oshanswers/ergonomics/