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The quick brown foxThe quick brown fox
Hand Intensive Work:
Predicting the Demand of a Manual Activity
Richard Wells
Department of Kinesiology, University of Waterloo
Hand Activities
Hold a hammer
Push hose on pipe
|| ?
Use a key to open a lock
Hold a plate of food
|| ?
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
Y, MyY, My
Z, Z, MzMz
X, X, MxMxY, MyY, My
Z, Z, MzMz
X, X, MxMx
R. W
ells
Prehensile GripsCylindrical/Prismatic Grips Grips with Pulp/tip Contact
Non-Prehensile or Force Dependant “Grips”Hook “Press”
Palm Pulp Press, Thumb/Finger Tips 2/3/4/5,
Sphere `Tripod TipsKey/Lateral Pinch
Side Opposition Grip
A/B)
X)
T)
Y)
F)
K)J) E)
G)
R)
Z)Increasing force and size Decreasing Forces and Size
Increasing dexterity
Fingers 2/3/4/5 Carry Box
T+F)
X+F)K’)
M)
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
Y, MyY, My
Z, Z, MzMz
X, X, MxMxY, MyY, My
Z, Z, MzMz
X, X, MxMxFF
External +Demand3Forces3Moments
Internal <=>Demand1 Force
Pressure <=>Distribution
Musculo-skeletal Tissue Loading(Internal Exposure/Dose Rate)
R. W
ells
R. W
ells
Wrench Defined
Exertion of hand on environment described by “wrench” (3 forces and 3 moments) expressed about the centre of the grip
Y, MyY, MyX, MxX, Mx
Z, MzZ, Mz
Y, MyY, My
X, MxX, Mx
Z, MzZ, Mz
R. Wells
Hand Actions
Because of the asymmetry of the hand there are 13 possible actions
Extend Ulnar Radial Supinate Pronate
Push Pull Push Up Push Down Push to Side Push to Side
Flex
Power Grip
Example: A Drilling Task
5 Nm Torque
1.2 kg. Mass
60N Feed Force
0-60
12.603.1-502
Wrench =
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
Hand Relative Action Demand*
0-60
12.603.1-502
Wrench =
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
0-60
12.603.1-502
0-60
12.603.1-502
Wrench =
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
Hand Relative Action Demand*
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)
ThereforeNeed 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 CapabilitiesSpecially 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
Height
(m) Weight
(kg) Age
(years)
Grip Strength
(N) Females
(n=10) 1.59 70.6 33.4 302.0 SD 0.07 24.4 11.9 43.0
Males (n=10) 1.78 82.3 32.7 450.0 SD 0.07 15.2 11.3 60.0
Example Data
Maximum Moments about Grip Centre:
Moment N.m (SD) Pronator Supinator
Radial Deviator
Ulnar Deviator Extensor Flexor
Female 4.7 (1.7) 4.9 (1.6) 6.2 (2.7) 7.7 (1.9) 6.2 (1.8) 7.1 (2.3) n 10 10 10 10 10 10
Male 8.1 (2.3) 8.0 (1.9) 10.3 (3.5) 13.0 (4.2) 8.2 (1.7) 9.3 (2.0) Power Grasp
n 10 10 9 9 8 8
Female 1.9 (0.6) 2.2 (1.0) 2.0 (0.6) 1.1 (0.2) 0.8 (0.3) 0.9 (0.4) n 9 9 8 8 8 8
Male 3.8 (1.1) 3.5 (0.8) 3.0 (1.1) 1.7 (0.5) 0.9 (0.3) 1.3 (0.6) Lateral Pinch
n 10 10 9 9 9 9
Female 1.3 (0.4) 1.9 (0.7) 1.1 (0.6) 2.0 (0.9) 1.8 (0.7) 1.5 (0.5) n 10 10 9 9 10 10
Male 2.2 (0.4) 2.4 (0.8) 1.7 (0.3) 2.6 (0.9) 2.6 (0.8) 2.1 (0.6) Pulp
Pinch n 9 10 9 8 10 10
Electromyography (EMG)
8 Sites
EMG/RPE vs Exertion
Lateral Pinch, One Participant, All Muscles
0
0.2
0.4
0.6
0.8
1
-200 -100 0 100 200
Push N Pull
Pro
po
rtio
n o
f M
axim
um
ECU
ED
ECR
FDI
FCU
FCR
FDS
FPL
RPE
Max limited by balance, shoulder strength?
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 Calculator
20 Participants10 M 10 F
Multiple Linear Regression by ParticipantEMG1 = 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
3 x Force, 3 x MomentPercentile 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
=
0-60
12.603.1-502
Wrench =
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
Hand Relative Action Demand*
0-60
12.603.1-502
Wrench =
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
0-60
12.603.1-502
0-60
12.603.1-502
Wrench =
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force
~0 >13%>7%17%33%~0%2%
Hand Relative Action Demand*
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-UpsPerceived 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
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?
Current and Future Work
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. Wells, R. and Greig, M. Characterising human hand prehensile capabilities by force and moment wrench, Ergonomics, 15;44(15):1392-402, 2001.
2. 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..
3. 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.