Transcript Musculoskeletal Disorder (MSD) Prevention

Hand Intensive Work:
Predicting the Demand of a
Manual Activity
Richard Wells
Department of Kinesiology, University of Waterloo
Hand Activities
Hold a hammer
|| ?
Use a key to open a lock
|| ?
Hold a plate of food
Push hose on pipe
Hand Strength
Characterizing human hand capabilities or
demand created by occupational tasks has
been mainly accomplished by measuring the
maximum force exerted on a handgrip
dynamometer or similar transducer.
How many people squeeze handgrip
dynamometers at work?!!
Hand Grip Strength
If the occupational activity is:
not a power grip or a pinch
on an isolated object or involves combinations of
actions, such as exerting moments and forces,
how well does the handgrip dynamometer
strength characterize the demand and load on
the tissues of the hand and forearm?
Hand Prehension Description
Two Parts
1. The geometry of
the hand/object
interaction
2. The forces and
moments
applied on the
environment
Prehensile Grips
Cylindrical/Prismatic Grips
Side Opposition Grip
Grips with Pulp/tip Contact
Key/Lateral Pinch
Sphere
`Tripod
Tips
A/B)
F)
T)
T+F)
X)
Y)
Z)
J)
K)
E)
K’)
X+F)
Increasing force and size
Decreasing Forces and Size
Increasing dexterity
Non-Prehensile or Force Dependant “Grips”
Hook
Fingers 2/3/4/5
Carry Box
“Press”
Palm
Pulp Press, Thumb/Finger Tips 2/3/4/5,
G)
M)
R)
Typical Tool Use for Grip Types
A/B Pistol grip on in-line screw
runner
T) Hammer (also T+F)
X) Carry or hold with small
handles
Y) Pliers
Z) Screw-driver
J) Hold parts/objects
F) Key
K) Small prismatic objects
E) Small prismatic objects
K’) Pen, pencil, scriber, dental
tool
G) Carrying with handle. Pull on
wrench. Single finger(s) may
operate trigger. Also carry
boxes
M) Apply force, support tray, hand
hammer
R) Sensory or apply force to seat
or insert part
Part 2: Forces and Moments
Exerted on Objects
Wrench Defined
Exertion of hand on environment described by
“wrench” (3 forces and 3 moments) expressed
about the centre of the grip
Z, Mz
Z, Mz
Y, My
Y, My X, Mx
X, Mx
R. Wells
Hand Actions
Because of the asymmetry of the hand
there are 13 possible actions
Power Grip
Push
Extend
Pull
Flex
Push Up
Ulnar
Push Down
Radial
Push to Side
Push to Side
Supinate
Pronate
Example: A Drilling Task
5 Nm Torque
1.2 kg. Mass
60N
Feed Force
Hand
Action
Wrench =
0
-60
12.60
3.1
-5
0
2
Fx
Fy
Fz
Mx
My
Mz
Fgrip
Palmar/Volar
Pull/Push
Radial/Ulnar
Ulnar/Radial
Pron/Supinator
Flexor/Extensor
Grip/Pinch force
Relative
Demand*
~0
>13%
>7%
17%
33%
~0%
2%
Measures of Hand Capabilities?
Most studies measure 1 or 2 of these
components
Most studies use wrist moments or
pinch/grip forces
No data on combined actions (e.g. pronate
and pull)
Therefore
Need to collect all forces and moments about
centre of the grip
Measurement
Thirteen randomized actions, about the orthogonal
axes in 3 grip types (power, lateral, and pulp
pinch), as well as combined activities, were
performed at maximal and sub-maximal levels in
mid pronation and a naturally adopted wrist
extension posture.
Measurement of Capabilities
Specially developed
dynamometer
measured the three
force and moment
components as
well as the pinch or
power grip forces.
Population
Working men and women with recent
manual work experience recruited from
industrial temporary agency
Females
(n=10)
SD
Males (n=10)
SD
Height
(m)
Weight
(kg)
Age
(years)
Grip
Strength
(N)
1.59
0.07
1.78
0.07
70.6
24.4
82.3
15.2
33.4
11.9
32.7
11.3
302.0
43.0
450.0
60.0
Example Data
Maximum Moments about Grip Centre:
Moment N.m (SD)
Radial
Pronator Supinator Deviator
Power
Grasp
Lateral
Pinch
Pulp
Pinch
Ulnar
Deviator Extensor
Flexor
Female
n
4.7 (1.7) 4.9 (1.6) 6.2 (2.7) 7.7 (1.9) 6.2 (1.8) 7.1 (2.3)
Male
n
8.1 (2.3) 8.0 (1.9) 10.3 (3.5) 13.0 (4.2) 8.2 (1.7) 9.3 (2.0)
Female
n
1.9 (0.6) 2.2 (1.0) 2.0 (0.6) 1.1 (0.2) 0.8 (0.3) 0.9 (0.4)
Male
n
3.8 (1.1) 3.5 (0.8) 3.0 (1.1) 1.7 (0.5) 0.9 (0.3) 1.3 (0.6)
Female
n
1.3 (0.4) 1.9 (0.7) 1.1 (0.6) 2.0 (0.9) 1.8 (0.7) 1.5 (0.5)
Male
n
2.2 (0.4) 2.4 (0.8) 1.7 (0.3) 2.6 (0.9) 2.6 (0.8) 2.1 (0.6)
10
10
9
10
10
9
10
10
9
10
10
10
10
9
8
9
9
9
10
9
8
9
9
8
10
8
8
9
10
10
10
8
8
9
10
10
Electromyography (EMG)
8 Sites
EMG/RPE vs Exertion
Lateral Pinch, One Participant, All Muscles
Max limited by balance,
shoulder strength?
1
Proportion of Maximum
ECU
0.8
ED
ECR
0.6
FDI
FCU
0.4
FCR
FDS
FPL
0.2
RPE
0
-200
-100
0
Push
N
100
Pull
200
EMG/RPE vs Exertion
Pulp Pinch, One Participant, All Muscles
EMG/RPE vs Exertion
Power Grip, Flexor Carpi Ulnaris, All Participants
Hand Demand Calculator
Analysis
20 Participants
10 M 10 F
Multiple Linear Regression by Participant
EMG1 = f (3 x Force, 3 x Moment)
EMG2 = f (3 x Force, 3 x Moment)
…..
EMG8 = f (3 x Force, 3 x Moment)
RPE = f (3 x Force, 3 x Moment)
Regression Coefficients
Calculator
3 x Force, 3 x Moment
Percentile of population
Predicted;
8 EMG and RPE
Hand Demand Calculator: 1
Hand Demand Calculator: 12
Does The Method Describe the
Demand on the Hand?
Compare the perceived exertion and EMG
for an action and the same action described
as a wrench and performed on the test
apparatus
=
Wrench =
0
-60
12.60
3.1
-5
0
2
Fx
Fy
Fz
Mx
My
Mz
Fgrip
Ha
Act
Palmar/V
Pull/Push
Radial/U
Ulnar/Ra
Pron/Sup
Flexor/Ex
Grip/Pin
Test Tasks 1
Test Tasks 2
EMG for Tasks and Their Mock-Ups
Extensor Digitorum
Slope = 1.042 R2= 0.93
RPE for Tasks and Their Mock-Ups
Perceived Exertion
Slope = 1.11 R2= 0.929
The Wrench Demand Description
The wrench demand description appears to
adequately describe the demand on the
forearm hand system
Current and Future Work
Two new grips added, “”volar diagonal” and
three finger “tripod” pinch
Adding these grips to the “Calculator”
How to make the technique available?
As part of “Ergowatch”?
Web available calculator?
Summary
Existing methods of hand demand evaluation were
deemed inadequate
A description of hand activities was developed that
accounts for the demand of a manual activity
Experimental testing of working Canadian men and
women while performing a wide range of hand
activates allowed creation of relationships between
the external task definition and its demand
A “ hand demand calculator” was developed for
evaluation and design
References
1.
2.
3.
Wells, R. and Greig, M. Characterising human hand prehensile
capabilities by force and moment wrench, Ergonomics,
15;44(15):1392-402, 2001.
Greig, M. and Wells, R. (2004) Measurement Of Prehensile Grasp
Capabilities By A Force And Moment Wrench: Methodological
Development And Assessment Of Manual Workers, Ergonomics,
47(1); 41-58..
Morose, T., Greig, M., and Wells, R. (2004) Utility of using a force
and moment wrench to describe hand demand, Occupational
Ergonomics, 4:1-10.