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Load Moment. Muscle Force. 5. Goals:. To to identify work related factors that increased the risk of reporting low back pain (LBP). To study the relative contribution of physical and psychosocial factors to the reporting of low back pain. Shear. Compression.

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ontario universities back pain study

Load Moment

Muscle Force



To to identify work related factors that increased the risk of reporting low back pain (LBP)

To study the relative contribution of physical and psychosocial factors to the reporting of low back pain



Muscles must pull with enough force to balance the load moment. High muscle force causes high compression.

High pull forces or a forward inclined trunk both cause high shear. Loss of muscle force & reliance on ligaments increases shear

Gary McCullough, Manager of the Oshawa Car Assembly Plant (centre) joins University of Waterloo researcher Patrik Ingelman and employee Ted Jones during workplace exposure assessment. Taken from: GM TODAY Autumn/ Winter 1995.

Loads on the low back were estimated from the electrical signals given off by the contraction of the extensor muscles of the spine. These were converted into spinal loads using a calibration process. Workers wore the equipment for an average of four hours.

Gary McCullough with Oshawa Car Assembly Plant employee Ted Jones. Photo shows the EMG electrode positions.Taken from: GM TODAY Autumn/ Winter 1995.


Both physical and psychosocial factors were associated with the reporting of low back pain. Both factors should therefore be addressed in the design and modification of work.

These data allow us to identify the probability of reporting LBP for particular levels of exposure. This is potentially usable for establishing job analysis methods and design target values.

Ontario Universities Back Pain Study

UW: R. Norman, R. Wells, P. Neumann

IWH: J. Frank, H. Shannon, M. Kerr

Risk Factors for LBP

All methods were developed specifically for this study and all shared a common metric. This allowed us to estimate loading on the low back for all the methods described

There has been considerable debate about the work-relatedness of low-back pain (LBP), North America’s most common occupational health problem. This study was specifically designed to address this debate, with a special interest given to collecting comprehensive workplace exposure data.

The reporting of LBP was found to be a function of both the physical demands of the jobs and a number of worker perceptions. The significant biomechanical risk factors which independently predicted the reporting of low back pain were:

1) peak hand forces,

2) peak shear force in the low back,

Study Site

This work was funded by the Institute for Work & Health, an independent not-for-profit research organization whose core funding is provided by the Workplace Safety & Insurance Board of Ontario, Canada.

The authors would like to acknowledge all of the members of the Ontario Universities Back Pain Study (OUBPS) working group:

From the Institute for Work and Health: Beaton D.E., Bombardier C, Ferrier S, Hogg-Johnson S, Mondloch M, Peloso P, Smith J, Stansfeld S.A., and Tarasuk V.

From the University of Waterloo: Andrews D.M., Dobbyn M, Edmondstone M.A., Ingelman J.P., Jeans B, McRobbie H, Moore A, Mylett J, Outerbridge G, and Woo H.

The OUBPS working group would like to thank management at all levels at General Motors of Canada Ltd. for providing access to the study site and work force, the on-site expertise of Mr. Elmer Beddome, the Canadian Auto Workers’ Union for endorsing participation and Mr. John Graham for on-site assistance, the Occupational Health Nurses and all of the GM medical staff. We extend a special thanks to the many employees who donated considerable non-work time and volunteered to have their work monitored in this study.

More than 350 workers, representing over 250 jobs, participated in the study conducted at Oshawa, one of the largest automotive assembly operations in the world and employing over 10,000 people.

Between 1994 and 1996 the study enrolled 137 people who reported low back pain (cases) and 179 unmatched people chosen at random from the three assembly plants at Oshawa. About one third worked at maintenance, skilled trades and relief work and the remainder worked on short cycle assembly tasks.

Posture and load variables were obtained from video by a computer assisted tracking system. The video was replayed under computer control and the operator tracked trunk position in three planes using a “video game” joystick.

On average the peak shear (maximum back-to-front force between vertebrae) was significantly greater for cases than for controls.

On average the cases bent over significantly faster (Peak Flexor Velocity) than did the controls

On average the cumulative spinal compression was significantly greater for cases than for controls

3) cumulative compressive force on the low back over a shift,

4) peak velocity of trunk movement.

Some of the variables were indicators of “peak” (one time highest observed) forces on the low back. Some of them are indicators of “accumulated forces” on the low back.

The significant psychosocial factors which independently predicted the reporting of low back pain were:

1) a high perceived physical load

2) low opinion of the workplace social environment,

3) perception of lack of control of the job,

4) high co-worker support,

5) high job satisfaction,

6) perceived over-education, and

7) a prior WCB claim.

When compared to more accurate methods (OS) the trained operators (OP) could accurately match the motions of the trunk.

Measurement of Workplace Exposure

In-home interviews were used to assess individual (e.g. height, marital status), clinical(e.g. pain, range of motion) and psychosocial (perceptions of the work environment and organization) variables. The physical demands were assessed by direct workplace measurements on individuals performing their usual job. A wide range of approaches were used to document the physical demands of work including: Questionnaire, Trained Observer, Posture and Load, Sampling, Video Analysis, Postural Analysis, Electromyography (EMG) and Vibration measurement.

Andrews, D, Norman, R.W., Wells, R.P, and Neumann, P. 1996 Accuracy and Repeatability of Low Back Spine Compression Force Estimates From Self Reports of Body Posture During Load Handling,International Journal of Industrial Ergonomics,18:251-260.

Neumann, P., Wells, R., Norman, R., Frank, J., Shannon, H., Kerr, M. Peak Spinal Loading as a Risk Factor for Low Back Pain Reporting in the Automotive Industry: An Inter-Method Comparison of a Common Metric, Submitted to Scandinavian Journal Work Environment and Health.

Norman, R.,Wells, R., Neumann, P., Frank, J., Shannon, H. and Kerr, M. 1998 A Comparison of Peak vs Cumulative Physical Loading Factors for Reported Low Back Pain in the Automobile Industry. In Press,Clinical Biomechanics, .

Wells, R. Norman, R. Neumann, P. Andrews, D. Frank,J. Shannon, H. and Kerr, M. 1997 Assessment of physical work load in epidemiologic studies: common measurement metrics for exposure assessment, Ergonomics, 40(1):51-61.