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

Prehensile Grips Cylindrical/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 Tips Key/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

Wrench Defined Exertion of hand on environment described by “wrench” (3 forces and 3 moments) expressed about the centre of the grip Y, My X, Mx Z, Mz Y, My X, Mx Z, 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 Flex Power Grip

Example: A Drilling Task 5 Nm Torque 1.2 kg. Mass 60N Feed Force

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

Example Data Maximum Moments about Grip Centre:

Electromyography (EMG) 8 Sites

EMG/RPE vs Exertion Lateral Pinch, One Participant, All Muscles 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 AnalysisCalculator 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 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 =

Test Tasks 1

Test Tasks 2

EMG for Tasks and Their Mock-Ups Extensor Digitorum Slope = R 2 = 0.93

RPE for Tasks and Their Mock-Ups Perceived Exertion Slope = 1.11 R 2 = 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): , 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); 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.