A biomechanical model of the lumbosacral joint for lifting activities

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ABSTRACTS OF THE SEVENTH ANNUAL CONFERENCE AMERICAN SOCIETY OF BIOMECHANICS

OF THE

Held at the Mayo Clinic, Rochester, Minnesota, 28-30 September 1983 A BIOMECHANICAL

MODEL

OF THE LUMBOSACRAL ACTIVITIES

JOINT

FOR LIFTING

CHARLES K. ANDERSON

A biomechanical model of the lumbosacral region was constructed for the purpose of systematically studying the stresses and strains on the local ligaments, muscles and disc during sagittal plane two-handed lifting. On the basis of model sensitivity analyses and analysis of actual job data it was concluded that typical lifting tasks can lead to excessive disc compressive forces, muscle moment generation requirements, and possibly lumbodorsal fascia strains, particularly if the task is repetitive. Conversely, annulus rupture directly due to tissue strain appears very unlikely. The relation of stress and strain estimates to the incidence of low-back pain was also studied. It was found that there is an increase in incidence rate for jobs having high lumbodorsal fascia strains, disccompression and muscle force required for trunk extension. AN EVALUATION

OF HANDLE

SHAPES

AND FORCES

DAVID J. COCHRAN and MICHAEL W. RILEY

The biomechanical forces exerted by the hand in grasping a handle are complex. Because of the extreme complexity of the human hand and the vast differences in anthropometric measurements and strengths of individual hands, strict biomechanical modeling of grasp, as it is affected by the item to be grasped, is as yet infeasible. This research attempts to evaluate empirically the effects of handle shape on the hand’s ability to resist or exert force in six directions. Thirty-six handles of four sizes and nine shapes were tested for maximum force exertion by both males and females. The results showed that different handle shapes and sizes were associated with high and low forces for each of the six directions. This suggests that handles which are associated with high forces on one of the six directional tests are probably suited for tasks which incorporate that type of force or movement and may not be appropriate for other tasks which do not. MEASUREMENTS

OF LOADS UPON THE LUMBAR SPINE DURING ISOKINETIC LIFTING ACI-IVITIES

ISOMETRIC

AND

W. S. MARRAS (Ohio State University, Columbus, OH 43210, U.S.A.) R. L. JOYNT and A. I. KING (Wayne State University, Detroit, MI 48202, U.S.A.) Ten male and ten female subjects were tested for their ability to produce maximal force about the lumbro-sacral junction (as is done during lifting) under controlled isometric and isokinetic conditions. The myoelectric activity of ten trunk muscles, the intra-abdominal pressure and the torque produced by the back were monitored in response to the experimental conditions. The results indicate that there are prominent differences in the manner in which subjects utilize the musculature of the trunk for the production of torque statically and dynamically. A significant time lag was identified between the onset of intra-abdominal pressure and torque and this lag also increased with increasing trunk velocity. These dilTerences between isometric and isokinetic exertions suggest that isokinetic trunk testing provides a means ofcontrolled evaluation which isappropriate for manual materials handling situations. A PROBABLE

ETIOLOGY

OF MECHANICAL

LOW BACK PAIN

JAVES A. PORTERFIELD(Physical Fitness Testing Center, Akron City Hospital, 525 E. Market Street,

Akron, OH 44309. U.S.A.) Abnormal asymmetrical antigravity biomechanics often accompanies musculoskeletal symptomafology. Asymmetrical skeletal dimensions coupled with the decreased stabilizing effect of our musculature as we age, alters the way in which our contractile and noncontractile soft tissues bear weight. Those with poor antigravity biomechanics render the contractile and noncontractile tissues of their musculoskeletal system vulnerable to increased wear patterns and spraining and straining, which often translate to symptoms. In effect, people with a67