Hand Intensive Work:

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• Hand Intensive Work
• Predicting the Demand of a Manual Activity
• Richard Wells
• Department of Kinesiology, University of Waterloo

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Hand Activities
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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?!!

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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?

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Hand Prehension Description

• Two Parts
• The geometry of the hand/object interaction
• The forces and moments applied on the environment

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Prehensile Grips
Side Opposition Grip
Grips with Pulp/tip Contact
Cylindrical/Prismatic Grips
Key/Lateral Pinch
Sphere Tripod Tips
A/B)
F)
T)
TF)
X)
K)
J)
E)
Y)
K)
XF)
Increasing force and size Decreasing Forces
and Size
Z)
Increasing dexterity
Non-Prehensile or Force Dependant Grips
Hook
Press Palm Pulp Press, Thumb/Finger
Tips 2/3/4/5,
Fingers 2/3/4/5 Carry Box
G)
M)
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Typical Tool Use for Grip Types

• A/B Pistol grip on in-line screw runner
• T) Hammer (also TF)
• 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

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Part 2 Forces and Moments Exerted on Objects
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Wrench Defined

• Exertion of hand on environment described by
  wrench (3 forces and 3 moments) expressed
  about the centre of the grip

R. Wells
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Hand Actions

• Because of the asymmetry of the hand there are 13
  possible actions

Power Grip
Push Down
Push Up
Push
Pull
Push to Side
Push to Side
Extend
Flex
Ulnar
Supinate
Radial
Pronate
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Example A Drilling Task

• 5 Nm Torque
• 1.2 kg. Mass
• 60N Feed Force

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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

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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.

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Measurement of Capabilities

• Specially developed dynamometer measured the
  three force and moment components as well as the
  pinch or power grip forces.

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Population

• Working men and women with recent manual work
  experience recruited from industrial temporary
  agency

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Example Data

• Maximum Moments about Grip Centre

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Electromyography (EMG)

• 8 Sites

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EMG/RPE vs Exertion

• Lateral Pinch, One Participant, All Muscles

Max limited by balance, shoulder strength?
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EMG/RPE vs Exertion

• Pulp Pinch, One Participant, All Muscles

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EMG/RPE vs Exertion

• Power Grip, Flexor Carpi Ulnaris, All Participants

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Hand Demand Calculator

• Analysis Calculator

20 Participants 10 M 10 F
3 x Force, 3 x Moment Percentile of population
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)
Predicted 8 EMG and RPE
Regression Coefficients
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Hand Demand Calculator 1
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Hand Demand Calculator 12
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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

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Test Tasks 1
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Test Tasks 2
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EMG for Tasks and Their Mock-Ups

• Extensor Digitorum
• Slope 1.042 R2 0.93

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RPE for Tasks and Their Mock-Ups
Perceived Exertion Slope 1.11 R2 0.929
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The Wrench Demand Description

• The wrench demand description appears to
  adequately describe the demand on the forearm
  hand system

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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?

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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

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References

• Wells, R. and Greig, M. Characterising human
  hand prehensile capabilities by force and moment
  wrench, Ergonomics, 1544(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,
  41-10.