SEPARATION AND SUMMATION OF EMG RECORDINGS BY TASK USING VIDEO RECORDS
Anne Moore, Richard Wells, Dwayne Van Eerd, Stephen Krajcarski, Melanie Banina, Donald Cole,
and Sheilah Hogg-JohnsonYork University, Toronto, Canada
University of Waterloo, Waterloo, Canada Institute for Work and Health, Toronto Canada
Introduction
Exposure to musculoskeletal loading at work depends on many factors (Wells et al)
-tasks performed, workload
-workstation, equipment, technique-task-time organization
Difficult to separate out the effects of each factor from overall level of musculoskeletal loading
Introduction – cont’d
Combining EMG and task identification using video has shown promising results in industry (Formsan et al, 2002)
Can we differentiate between tasks in an office setting even when these tasks are done within an environment of other tasks that may or may not be done simultaneously?
Methods
33 Participants: –Newspaper advertising and finance employees–Clerical, administration, sales, customer accounts and call centre–10 male/ 23 female
Methods (cont’d)
Electromyographic signals bilaterally from:
–Extensor Carpi Ulnaris Brevis (ECRB)–Trapezius
Recorded using portable EMG system (ME3000P8, Mega Electronics, Finland)
Simultaneous video recording
Protocol
Participant reported to a private room for hook up, signal verification and calibration:
–Maximal shoulder shrug with arms abducted against resistance–Wrist extension with maximal grasp
Participant and researcher returned to participant’s usual workstation
Protocol
EMG and video recorded while participant performed usual job for 2 hours
Subset repeated protocol on a 2nd day (n=20)
Video Analysis
30 minutes of Video chosen for analysis based on:
–Included “mark” for time synchronization–Emphasis on seated work
On/off states of 7 tasks identified while viewing video and simultaneously recorded on computer (Observer Pro 4.0, Noldus Technology, Netherlands)
Video Analysis (cont’d)
Seven states/activities identified:
State “On” Definition
1 Keying On/Off Either hand in contact with keyboard or poised as if to use
2 Mousing On/Off Hand in contact with mouse or poised as if to use
3 Phone On/Off Hand grasps handset of phone
4 DeskworkOn/Off
Visibly working with job relevant items on desk
5 Sitting/Standing Buttocks are in contact with seat pan
6 At desk/Away Subject recognized to be at workstation or in camera view
7 Other On/Off Cannot be assigned to first 4 states and occurs simultaneously
EMG Analysis
Custom software performed:
–Link in time with video file–EMG calibration–Amplitude Probability Distribution Function (APDF) at 10th, 50th, and 90th level (Jonsson, 1982)
–Gaps Analysis (Veiersted et al, 1990)
All analyses performed at:–Whole file level–General Task level (individual and concatonated)–Specific Group level (individual and concatonated)
0
10
20
30
40
50
0 1 2 3
Time (min)
0
10
20
30
40
50
0 1 2 3 4 5 6Time (min)
-10
0
10
20
30
40
50
0 1 2 3 4 5 6 7 8 9 10Time (min)
EM
G (
% M
VC
)
Task Identification and Concatonation Process
Results
Keyboarding – Static EMG
0
0.5
1
1.5
2
2.5
3
Rt ECRB Rt Traps Lt ECRB Lt Traps
Stat
ic E
MG
(%
MV
C)
keyoff
keyon
*
*
*
*
Keyboarding - Gaptime
0
5
10
15
20
R.ECRB R. Traps L. ECRB L. Traps
Gap
tim
e (s
ec/m
in)
Keyoff
Keyon*
*
Mousing – Static EMG
0
1
2
3
4
5
Rt ECRB Rt Traps Lt ECRB Lt Traps
Stat
ic E
MG
(%
MV
C)
mouse off
mouse on
*
*
Mousing – Peak EMG
0
5
10
15
20
25
Rt ECRB Rt Traps Lt ECRB Lt Traps
Pea
k E
MG
(%
MV
C)
mouse off
mouse on
*
*
*
Phone – Static EMG
0
0.5
1
1.5
2
R.ECRB R. Traps L. ECRB L. Traps
Stat
ic E
MG
(% M
VC
)
Phoneoff
Phoneon
Conclusions
Separating EMG by task in the workplace allows examination effects of specific tasks on musculoskeletal load in situ
Conclusions - continued
Use of a mouse is a constrained task that has high static muscle activity and low peak muscle activity in mouse hand
The period of time while keyboarding was marked by significantly higher static loading in both the forearms and shoulders
Acknowledgements
NIOSH/NIH R010H03708-02
Center for VDT & Health Research
Toronto Star
Southern Ontario Newspaper Guild