R.W. Marklin discusses ergonomics and various ergonomic issues related to work environments and product design. He defines ergonomics as evaluating how human strengths and limitations interact with products and work environments to maximize health, ease of use, and productivity. Marklin discusses three spheres of ergonomics - physical, cognitive, and organizational/social factors. He provides examples of ergonomic evaluations and recommendations for truck cab dimensions, computer keyboard designs, managing manhole covers, and laptop placement in utility vehicles. The document covers ergonomic principles and various case studies.

1. Ergonomics
R.W. Marklin, Ph.D., CPE
Professor, Mechanical Engineering
Oct. 3, 2012

2. What is Ergonomics
A Primer
R.W. Marklin, Ph.D, CPE
Certified Professional Ergonomist
Dept. of Mechanical Engineering
Marquette University

3. Etymology of Ergonomics
Ergo: work from Greek
Nomos: laws, customs
Ergonomics is etymologically laws or
customs of work
But we need a less abstruse definition in
order to understand ergonomics in the
contemporary world

4. Definition of Ergonomics
Ergonomics is the science of evaluating
and designing products and work
environments around the strengths and
limitations of the human user in order to:
Maximize occupational health
Maximize ease of use
Maintain productivity of user

5. PsychoSocial
Work Organization
Worker Satisfaction
Mgmt-Worker Rel.
Compensation.
Cognitive Factors
Mental workload
Physical Factors
Tools and Equipment
Methods of Task
Measure external
and internal forces (EMG)
Human
Operator
Industrial Hygiene
Noise
Heat/Cold
Chemicals R.W. Marklin is a
Physical Ergonomist
Three Spheres of Ergonomics

6. Truck Cab Dimensions

7. Cab Design
Seat Travel- Forward and Rear
Seat to Bulkhead Distance
Steering Wheel Height
Cab Ceiling Height
Pedal Location
Height between Cab Floor and IP
7

8. Insufficient Rear Travel
 Site Visit vehicle
 95th
percentile male
modeling by
Siemens Jack
 Worker’s legs
rotated outward
 Safety hazard and
postural discomfort
8

9. Insufficient Forward Seat Travelavel
 Site Visit vehicle
 5th
percentile female
modeling by
Siemens Jack
 Worker does have
full support from seat
back
9

10. Calculating Seat Travel
 Accelerator to Seat
Ref Point (SRP)
 SAE J4004 method
for calculating
forward and rear
seat travel
 EPRI 2010 utility
workers’ male
anthropometry
 Gen. pop female
anthropometry 10

11. Seat Travel Recommendations:
AV / DD Cab
11

12. Seat Travel Recommendations:
Pickup Cab
12

13. Seat to Bulkhead Distance
 Insufficient distance
may not allow driver
to recline seatback
sufficiently
13

14. Recommendation
 Recommended
minimum seat to
bulkhead distance is
15.7 in.
 Seat dimensions
taken from database
of 27 site visit
vehicles
14

15. Recommendation
 At least 42 in. height
from Seat Ref. Point
to cab ceiling
 Ht from cab floor to
SRP can vary –
reason to use SRP
 Based on 99th
percentile male utility
workers
15

16. Pedal Location
 Insufficient distance
between brake and
accelerator
 Toe stuck under
pedal
 Boot overlaps both
pedals
 Workers have larger
feet than gen. pop
 Some workers drive
vehicles without
boots
16
This cab has sufficient distance
between brake and accelerator but
not between accelerator and hump.

17. Recommendation
 EPRI 2010
anthropometry study:
99th
percentile shoe
size was 14D
 2 in. clearance
added to ½ of boot
width
 Center of accelerator
used to
accommodate big
boots (overlap with 17

18. Recommendation
 99th
percentile boot
size
 Vehicle database
used for dimensions
and angle of
accelerator
18

19. Computer Keyboards

20. Computer Keyboard Designs

21. Computer Keyboard Designs
Conventional keyboard
Split keyboard
Sloped keyboard
Tilted keyboard

23. Epidemiology & Keyboards
Tittirandonda, Burastero, and Rempel
(1999) summary
Consistent relationship between
computer-related risk factors and MSDs,
specifically sustained awkward postures
of wrist
This presentation will address how
alternative keyboard designs can reduce
awkward postures risk factor

24. How Do MSDs’ Risk Factors Relate
to Conventional Computer
Keyboards?
 Posture
 Extended wrist
 Ulnarly deviated wrist
 Repetition
 3 key strokes per second
 Up to 50,000 to 100 000 key strokes
per day
 Force
 Minimal forces but exerted many times

25. Wrist Deviation and Tendons

26. Cross-Section of Wrist
Trapezium
Flexor
digitorum
superficialis
tendon
Flexor
digitorum
profundus
tendon
Pisiform
Flexor pollicis
longus tendon
Flexor carpi
radialis
tendon
Flexor
retinaculum Median nerve
(Saidoff & McDonough, 2002)

27. Biomechanical Consequences
of a Deviated Wrist Position
 Friction of tendons across the carpal tunnel
 Requires more muscular effort due to friction and
contact forces
 May lead to tenosynovitis (friction causes irritation
of tendons, leading to inflammation, pain and
swelling)
 May lead to carpal tunnel
syndrome (swelling in the
carpal tunnel leads to
increased carpal
tunnel pressure)

28. Carpal Tunnel Pressure
Pressure against median nerve in carpal
tunnel could cause carpal tunnel
syndrome
Pressure against tendons and their
sheaths could cause tenosynovitis

29. Carpal Pressure (mm Hg) = f (wrist flex/ext)
0
10
20
30
40
50
60
70
-60 -40 -20 0 20 40 60
 Flexion * Extension 
(Rempel et al., 1997)

30. Split Keyboard
 Slant angle of a keyboard
 Split fixed-angle
 Split adjustable-angle
10.5° slant
12.5° slant
The slant angle is half the opening angle

31. Sloped Keyboard
Slope angle of a keyboard
 Positive slope keyboard
 Negative slope keyboard
15° slope
-15° slope

32. Tilted Keyboard
Tilt angle of a keyboard
 Vertically inclined keyboard
20° tilt

33. Conventional Keyboard Wrist Deviation
 Left hand
 Wrist Ulnar Dev.
 15.0 ± 7.7°
 Wrist Extension
 21.2 ± 8.8°
 Pronation
 62.2 ± 10.6°
 Right hand
 Wrist Ulnar Dev.
 10.1 ± 7.2°
 Wrist Extension
 17.0 ± 7.4°
 Pronation
 65.6 ± 8.3°
Simoneau et al. (1999)
N = 90 touch typists (approx. 60 wpm)
Age = 37.8 ± 9.3 years
Experience = 14.4 ± 8.8 years

34. Fixed-Angle Split Keyboard

35. Adjustable-Angle Split
Keyboard

36. Right Wrist Ulnar Deviation
Marklin et al. (2000)

37. Wrist Extension
Marklin et al., 2000

38. Summary of Split Keyboards
Split keyboards with opening angle of
20˚ to 25˚reduced ulnar deviation by
>10˚
Within 2˚ of neutral for right
Within 5˚ of neutral for left
Reduced wrist factor of ulnar deviation
No decrease in typing speed or accuracy

39. Recommended Keyboards

40. Electric Power Industry
Ergonomics Handbooks

41. EPRI Document
#1005199
November 2001

42. EPRI Document
#1005430
March 2004

43. EPRI Document
#1005574
March 2005

44. EPRI Document
#101042
January 2008

45. EPRI Document
#1014942
March 2008

46. Manhole Covers

47. Removing and Replacing Manhole Covers:
Current Work Practice
Manholes provide access to
underground vaults and utility corridors
Square: up to 3 ft x 4 ft
Round: up to 4 ft in diameter
123 to 209 lbs

48. Removing and Replacing Manhole Covers:
Current Work Practice
Hook and chain
Steel lifting hook

49. Removing and Replacing Manhole Covers:
Current Work Practice
1st
class lever with a magnet

50. Removing and Replacing Manhole Covers:
Current Work Practice
1st
class lever with a magnet

51. Removing and Replacing Manhole Covers:
Current Work Practice
2nd class lever

52. Removing and Replacing Manhole Covers:
Problems
High forces on shoulder and trunk
muscles – particularly using the hook
and chain and steel lifting hook

53. Removing and Replacing Manhole Covers:
Recommended Ergonomic Recommendations
1st
class lever with magnet
2nd
class lever

54. Removing and Replacing Manhole Covers:
Benefits of 1st
class lever with magnet
Based on field study with 32.5 inch 175 lbs
cover
Peak force with handle attached to 175 lbs
cover: 177 lbf
Peak force with 1st
class lever: 68 lbf

56. Removing and Replacing Manhole Covers:
Benefits of 1st
class lever with magnet
University of Michigan 3D SPPP based
on field study with 32.5 in. 175 lb cover:
Spinal compression with hook and chain:
over 2800 lbf
Spinal compression with 1st
class lever and
magnet: < 433 lbf
NIOSH safe limit = 770 lbf

57. Mobile Computers

58. Laptops in Utility Vehicles

59. Mobile Computer Laboratory Study
Investigate the effects of different laptop
PC locations in a utility vehicle cab
Biomechanical effects
Performance and safety effects
Subjective assessment

60. 60

61. Location on Passenger Seat
 On top and in front of
passenger seat

62. Location – Driver Side

63. Goniometers and EMG

64. Shoulder Angle

65. Laboratory Study:
Dependent Variables
Biomechanical
Body segment angles
 Neck angle (rotation and flexion)
 Shoulder (abduction and flexion)
 Elbow (flexion)
 Wrist (radial/ulnar deviation and
flexion/extension)
 Trunk (rotation and flexion)
Muscle force: EMG activity of major trunk,
shoulder and arm muscles
65

66. Laboratory Study:
Dependent Variables
Comfort and effort
Assessed using ordinal subjective
assessment forms
Performance
Time to complete tasks on PC
Accuracy of tasks
Preference
Rank order of placement from worst to best
Selection of best placement
66

67. Left Erector Spinae EMG
67
 Laptop on and in
front of passenger
seat (A & B)
increases left back
muscle force
substantially for both
tasks
L e ft E r e c to r S p in a e
N = 7
L o c a t i o n * T a s k ; W e i g h t e d M e a n s
V e rt i c a l b a rs d e n o t e 0 . 9 5 c o n f i d e n c e i n t e r v a l s
K e y b o a rd
T o u c h s c r e e n
0 . 1 7 5 2
0 . 1 0 3
0 . 0 4 0 4
0 . 0 6 0 1
0 . 1 7 5 2
0 . 1 0 3
0 . 0 4 0 4
0 . 0 6 0 1
0 . 1 8 2 6
0 . 1 4 5 8
0 . 0 8 8 0 . 0 8 7 9
0 . 1 8 2 6
0 . 1 4 5 8
0 . 0 8 8 0 . 0 8 7 9
A B C D
L o c a t i o n
0 . 0 0
0 . 0 5
0 . 1 0
0 . 1 5
0 . 2 0
0 . 2 5
0 . 3 0
Mean
0 . 1 7 5 2
0 . 1 0 3
0 . 0 4 0 4
0 . 0 6 0 1
0 . 1 8 2 6
0 . 1 4 5 8
0 . 0 8 8 0 . 0 8 7 9

68. Right Deltoid EMG
68
 Laptop on and in
front of passenger
seat (A & B)
increases right
shoulder force
substantially for
touchscreen tasks
R ig h t D e lto id
N = 2 2
L o c a t i o n * T a s k ; W e i g h t e d M e a n s
V e r t i c a l b a r s d e n o t e 0 . 9 5 c o n f i d e n c e i n t e rv a l s
K e y b o a r d
T o u c h s c re e n
A B C D
L o c a t i o n
0 . 0 0
0 . 0 5
0 . 1 0
0 . 1 5
0 . 2 0
0 . 2 5
0 . 3 0
Mean

69. Recommended
Location of Laptop

70. Subjective Assessment
 Subjects
overwhelmingly
liked the locations
near driver seat
 Disliked the locations
near passenger seat
Q u e s t io n 3 : M e d ia n R e s p o n s e
N = 2 2
4 . 0
5 . 0
5 . 5
2 . 0
0 1 2 3 4 5 6
BC
D A
4 . 0
5 . 0
5 . 5
2 . 0

71. Wind Turbines

72. Wind Turbines – Enormous, Plentiful
(>15,000 in US), and Growing

73. Lakeshore Technical College
 135 ft. wind turbine
 24 new students each
year
 100% placement
 1 hour drive from
Milwaukee
73

74. Wind Power Maintenance
Tasks
Inspection and maintenance
Oil exchange and filters
Check torque on bolts
Parts removal and replacement
74

75. Wind Turbine Site Visit
Texas site

76. Wind Turbine Site Visit
Tasks in Nacelle (box on top to tower)
8 ft tall, 8 ft wide, 20 ft long

77. Muchas Gracias