Transcript No Slide Title

Department of
Kinesiology,
University of
Waterloo
OPTIMAL UPPER LIMB SUPPORT
CONDITIONS FOR MOUSE USE?
Richard Wells
Rationale
Department of
Kinesiology,
University of
Waterloo
 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 joint
FOREARM; 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
Questions
Department of
Kinesiology,
University of
Waterloo
What changes with different support conditions
Which is optimal?
What are appropriate outcome (dependant) measures?
Answers to these questions will inform recommendations
on the best practice for mouse use
Dependent Measures
Department of
Kinesiology,
University of
Waterloo
Musculoskeletal strain
Electromyography of 8 muscles of the arm and shoulder
Wrist goniometry
Speed/Accuracy
Fitts’ tapping task
Pain and Discomfort
Tasks
Department of
Kinesiology,
University of
Waterloo
i) Drawing task;
ii) Interactive text editing task
iii) Fitts’ tapping task
iv) Extended game playing.
Electromyographic Sites
Department of
Kinesiology,
University of
Waterloo
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).
Normalization of the EMG
Department of
Kinesiology,
University of
Waterloo
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.
Wrist Posture Measurement
Department of
Kinesiology,
University of
Waterloo
 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.
Static EMG vs Support
Condition for Eight Muscles
Department of
Kinesiology,
University of
Waterloo
*
5
Elbow
Forearm
4
*
Shoulder (None)
3
Wrist
*
2
*
*
1
0
FDI
FDS
ED
ECU
Muscle
PT
Thru
Trap
Inf
Discomfort
Department of
Kinesiology,
University of
Waterloo
After 3 Hours
Mouse Use:
Support
N=5
Discomfort and Mouse Use
Department of
Kinesiology,
University of
Waterloo
After 3 Hours
Mouse Use:
Shoulder Support
N=5
Discomfort and Mouse Use
Department of
Kinesiology,
University of
Waterloo
After 3 Hours
Mouse Use:
Wrist Support
N=5
Discomfort and Mouse Use
Department of
Kinesiology,
University of
Waterloo
After 3 Hours
Mouse Use:
Elbow
Support
N=5
Discomfort and Mouse Use
Department of
Kinesiology,
University of
Waterloo
After 3 Hours
Mouse Use:
Forearm
Support
N=5
Findings
Department of
Kinesiology,
University of
Waterloo
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