Department of Kinesiology,University of Waterloo OPTIMAL UPPER LIMB SUPPORT

CONDITIONS FOR MOUSE USE?

Richard Wells

Department of Kinesiology,University of Waterloo

RationaleRationale

A number of recommendations for support of the mouse arm have appeared in the computer and RSI-related literature. These include: WRIST; planting the ventral surface of the wrist on the work surface and

moving the mouse from the wrist joint ELBOW; planting the elbow on the chair’s arm rest and moving the

mouse from the elbow jointFOREARM; resting the forearm on the work surface and moving the

mouse from the shoulder and SHOULDER; moving the mouse from the shoulder joint with the arm

unsupported

R. Wells, I.H. Lee, and S. Bao, 1996 INVESTIGATIONS OF THE OPTIMAL UPPER LIMB SUPPORT CONDITIONS FOR MOUSE USE, in: Proceeding of Human Factors Association of Canada

Department of Kinesiology,University of Waterloo

QuestionsQuestions

What changes with different support conditionsWhich is optimal?What are appropriate outcome (dependant) measures?

Answers to these questions will inform recommendations on the best practice for mouse use

Department of Kinesiology,University of Waterloo

Dependent MeasuresDependent Measures

Musculoskeletal strainElectromyography of 8 muscles of the arm and shoulderWrist goniometry

Speed/Accuracy Fitts’ tapping task

Pain and Discomfort

Department of Kinesiology,University of Waterloo

TasksTasks

i) Drawing task;

ii) Interactive text editing task

iii) Fitts’ tapping task

iv) Extended game playing.

Department of Kinesiology,University of Waterloo

Electromyographic SitesElectromyographic Sites

Electromyograms were collected from the right upper limb from surface electrodes overlying

1st dorsal interosseous (FDI), finger/wrist extensors (ED), extensor carpi ulnaris (ECU), flexor superficialis (FDS), pronator teres (PT), a combined flexor/extensor site (Thru)upper trapezius (Trap) infraspinatus (Inf).

Department of Kinesiology,University of Waterloo

Normalization of the EMG Normalization of the EMG

Against maximal efforts (MVIC), fixed effort contractions and µVolts.

Only EMG, quantified by the 10th percentile APDF values for the normalization to maximum efforts (%MVIC) will be reported here.

Department of Kinesiology,University of Waterloo

Wrist Posture MeasurementWrist Posture Measurement

recorded using flexible wrist goniometers (Penny and Giles) flexion/extension, ulnar/radial and pronation/supination

Two calibrations, statically to known angles and dynamically against a fixture instrumented to record wrist postures were made.

EMG and wrist posture were recorded for 3 minutes of continuous task performance.

Department of Kinesiology,University of Waterloo

Static EMG vs Support Static EMG vs Support Condition for Eight MusclesCondition for Eight Muscles

FDI FDS ED ECU PT Thru Trap Inf

0

1

2

3

4

5Elbow

Forearm

Shoulder (None)

Wrist

Muscle

* *

*

*

*

Department of Kinesiology,University of Waterloo

DiscomfortDiscomfort

After 3 Hours Mouse Use:

Support

N=5

Department of Kinesiology,University of Waterloo

Discomfort and Mouse UseDiscomfort and Mouse Use

After 3 Hours Mouse Use:

Shoulder Support

N=5

Department of Kinesiology,University of Waterloo

Discomfort and Mouse UseDiscomfort and Mouse Use

After 3 Hours Mouse Use:

Wrist Support

N=5

Department of Kinesiology,University of Waterloo

Discomfort and Mouse UseDiscomfort and Mouse Use

After 3 Hours Mouse Use:

Elbow Support

N=5

Department of Kinesiology,University of Waterloo

Discomfort and Mouse UseDiscomfort and Mouse Use

After 3 Hours Mouse Use:

Forearm Support

N=5

Department of Kinesiology,University of Waterloo

FindingsFindings

Based upon the above investigation the following findings are suggested:

1)The elbow support condition appeared to minimize the static load on the shoulder muscles sampled (trapezius and infraspinatus) and the forearm muscles

2)The shoulder support condition appeared to require the highest muscle activity in the shoulder muscles

3)The wrist support condition appeared to require the highest muscle activity in the muscles of the arm sampled