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Spine loading in response to whole body vibration: Is modeling with passive properties alone adequate?
470
Abstracts MECHANICAL
PROPERTIES
OF LS-Sl SPINE MOTION
SEGMENTS
K. M. JEPSEN, J. A. A. MILLER, A. B. SCHULTZand G. B. J. ANDERSON (Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor, MI 48109-2125, U.S.A.) The three-dimensional quasi-static load-displacement behavior of nine fresh adult L5-Sl motion segments was measured in nine test directions. Specimens were tested with, then without posterior elements. In response to a 160 N shear load applied to the superior endplate of the disc, the center of the LS vertebra of intact specimens displaced from 1.45 mm in lateral shear to 2.23 mm in posterior shear. In response to a 16 Nm moment mean displacements in the direction of loading ranged from 3.38’ in torsion to 7.69” in flexion. Removal of the posterior elements led to increases in displacements ranging from a factor of 1.46 in lateral shear to 2.74 in torsion. Comparison with published data from LI-LS levels shows the L5-SI segment is more flexible, and the L5-$1 posterior elements generally resist a larger percentage of an applied load than do those at other lumbar levels.
C. JOINT MECHANICS AND CONTROL
SPINE LOADING
IN RESPONSE TO WHOLE BODY VIBRATION: IS iMODELING PASSIVE PROPERTIES ALONE ADEQUATE?
WITH
R. ROMICK-ALLENand A. B. SCHULTZ(Department of Mechanical Engineering, University of Michigan, Ann Arbor, Ml 48109-2125, U.S.A.) Whole body vertical vibration of a sitting human was modeled to determine if experimentally observed resonances could be reproduced using passive value stiffness parameters. Over the range of 2-15 Hz, the sitting human exhibits vertical resonances at 4-5 Hz and bending resonances at 8-10 Hz. The sitting human was modeled as a system of elastically connected rigid bodies moving in the sagittal plane. Two, three and four-body models were considered. Buttocks axial and torso bending stiffnesses to provide these observed resonances were calculated. The required torso bending stiffness was on the order of 100 times higher than passive bending stiffnesses. Models to represent seated whole body vibration response seem to need to include active muscle contractions to adequately reproduce experimentally observed resonances.
LOW-BACK
MUSCLE
MODELS-A
SENSITIVITY
ANALYSIS
DON B. CHAFFIN,GUNNAR B. J. ANDERSON, GEORGE B. PAGE and DONALD S. BLOSWICK(University of
Michigan, U.S.A.) Manual lifting of heavy weights in industry and sports has been shown by epidemiological studies to cause or contribute to increased incidents resulting in disability due to low-back pain. It also is known that torso muscle actionsare the primary source ofstability and postural control of the lumbar motion segments. As such, the torso muscles also are the major source of spinal compression forces. This paper reviews two different biomechanical models of the low-back muscles commonly used to evaluate lifting spinal loads. The first model is a simple sagittal plane static model proposed by Morris, Lucas and Bressler in 1961, and enhanced by Chaffin and colleagues over the last two decades. The second is a three-dimensional static model which involves ten, fourteen and 22 muscles. It was first developed by Schultz and Andersson in 1981. This paper briefly reviews the logic used in each model, and systematically explores the effects of varied input conditions and assumptions when using the models to simulate a variety of lifting tasks.
ORGANIZATION
OF LIMB DYNAMICS
DURING
RAPID OSCILLATORY
MOVEMENTS
M. G. HOY, R. F. ZERN~CKEand J. L. SMITH (Department of Kinesiology, University of California, Los Angeles, CA 90024, U.S.A.) The paw-shake response (PSR) consists of rapid hindlimb oscillations (10-13 I-Ix)generated by cats to remove irritants from the paw. In contrast to the consistent recruitment of hindlimb muscles during the entire PSR, the
Abstracts MECHANICAL
PROPERTIES
OF LS-Sl SPINE MOTION
SEGMENTS
K. M. JEPSEN, J. A. A. MILLER, A. B. SCHULTZand G. B. J. ANDERSON (Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor, MI 48109-2125, U.S.A.) The three-dimensional quasi-static load-displacement behavior of nine fresh adult L5-Sl motion segments was measured in nine test directions. Specimens were tested with, then without posterior elements. In response to a 160 N shear load applied to the superior endplate of the disc, the center of the LS vertebra of intact specimens displaced from 1.45 mm in lateral shear to 2.23 mm in posterior shear. In response to a 16 Nm moment mean displacements in the direction of loading ranged from 3.38’ in torsion to 7.69” in flexion. Removal of the posterior elements led to increases in displacements ranging from a factor of 1.46 in lateral shear to 2.74 in torsion. Comparison with published data from LI-LS levels shows the L5-SI segment is more flexible, and the L5-$1 posterior elements generally resist a larger percentage of an applied load than do those at other lumbar levels.
C. JOINT MECHANICS AND CONTROL
SPINE LOADING
IN RESPONSE TO WHOLE BODY VIBRATION: IS iMODELING PASSIVE PROPERTIES ALONE ADEQUATE?
WITH
R. ROMICK-ALLENand A. B. SCHULTZ(Department of Mechanical Engineering, University of Michigan, Ann Arbor, Ml 48109-2125, U.S.A.) Whole body vertical vibration of a sitting human was modeled to determine if experimentally observed resonances could be reproduced using passive value stiffness parameters. Over the range of 2-15 Hz, the sitting human exhibits vertical resonances at 4-5 Hz and bending resonances at 8-10 Hz. The sitting human was modeled as a system of elastically connected rigid bodies moving in the sagittal plane. Two, three and four-body models were considered. Buttocks axial and torso bending stiffnesses to provide these observed resonances were calculated. The required torso bending stiffness was on the order of 100 times higher than passive bending stiffnesses. Models to represent seated whole body vibration response seem to need to include active muscle contractions to adequately reproduce experimentally observed resonances.
LOW-BACK
MUSCLE
MODELS-A
SENSITIVITY
ANALYSIS
DON B. CHAFFIN,GUNNAR B. J. ANDERSON, GEORGE B. PAGE and DONALD S. BLOSWICK(University of
Michigan, U.S.A.) Manual lifting of heavy weights in industry and sports has been shown by epidemiological studies to cause or contribute to increased incidents resulting in disability due to low-back pain. It also is known that torso muscle actionsare the primary source ofstability and postural control of the lumbar motion segments. As such, the torso muscles also are the major source of spinal compression forces. This paper reviews two different biomechanical models of the low-back muscles commonly used to evaluate lifting spinal loads. The first model is a simple sagittal plane static model proposed by Morris, Lucas and Bressler in 1961, and enhanced by Chaffin and colleagues over the last two decades. The second is a three-dimensional static model which involves ten, fourteen and 22 muscles. It was first developed by Schultz and Andersson in 1981. This paper briefly reviews the logic used in each model, and systematically explores the effects of varied input conditions and assumptions when using the models to simulate a variety of lifting tasks.
ORGANIZATION
OF LIMB DYNAMICS
DURING
RAPID OSCILLATORY
MOVEMENTS
M. G. HOY, R. F. ZERN~CKEand J. L. SMITH (Department of Kinesiology, University of California, Los Angeles, CA 90024, U.S.A.) The paw-shake response (PSR) consists of rapid hindlimb oscillations (10-13 I-Ix)generated by cats to remove irritants from the paw. In contrast to the consistent recruitment of hindlimb muscles during the entire PSR, the