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Resonance behaviour of the seated human body and effects of posture

Resonance behaviour of the seated human body and effects of posture
Resonance behaviour of the seated human body and effects of posture

Understanding of the resonance behaviour of the human body is important in the identification of vibration frequencies and body postures associated with back problems. In this study, experimental modal analysis was applied to whole-body vibration. Eight subjects were exposed to vertical random vibration while adopting three different postures on a rigid seat without a backrest. Motions of the spine, pelvis and viscera in the mid-sagittal plane were derived from skin-mounted accelerometers; head responses were measured using a bite-bar. Eight modes of vibration response were extracted below 10 Hz. A principal resonance of the human body at about 5 Hz consisted of an entire body mode, in which the skeleton moved vertically due to axial and shear deformations of buttocks tissue, in phase with a vertical visceral mode, and a bending mode of the upper thoracic and cervical spine. A bending mode of the lumbar and lower thoracic spine was found with a pitching mode of the head in the next higher mode located close to the principal mode. The second principal resonance at about 8 Hz corresponded to pitching modes of the pelvis and a second visceral mode. When subjects changed posture from erect to slouched, the natural frequency of the entire body mode decreased, resulting in a decrease in the principal resonance frequency. Shear deformation of buttocks tissue increased in the entire body mode due to the same change of posture. The complex body motions suggest that any forces causing injury from whole-body vibration will not be well-predicted by biodynamic models incapable of representing the appropriate body motions and the effects of body posture. It seems likely that the greatest risk of back problems will arise from the bending deformations of the spine.

Experimental modal analysis, Posture, Resonances, Whole-body vibration
0021-9290
143-149
Kitazaki, Satoshi
ed0e8233-d386-4446-b918-28ee2cd38553
Griffin, Michael J.
24112494-9774-40cb-91b7-5b4afe3c41b8
Kitazaki, Satoshi
ed0e8233-d386-4446-b918-28ee2cd38553
Griffin, Michael J.
24112494-9774-40cb-91b7-5b4afe3c41b8

Kitazaki, Satoshi and Griffin, Michael J. (1997) Resonance behaviour of the seated human body and effects of posture. Journal of Biomechanics, 31 (2), 143-149. (doi:10.1016/S0021-9290(97)00126-7).

Record type: Article

Abstract

Understanding of the resonance behaviour of the human body is important in the identification of vibration frequencies and body postures associated with back problems. In this study, experimental modal analysis was applied to whole-body vibration. Eight subjects were exposed to vertical random vibration while adopting three different postures on a rigid seat without a backrest. Motions of the spine, pelvis and viscera in the mid-sagittal plane were derived from skin-mounted accelerometers; head responses were measured using a bite-bar. Eight modes of vibration response were extracted below 10 Hz. A principal resonance of the human body at about 5 Hz consisted of an entire body mode, in which the skeleton moved vertically due to axial and shear deformations of buttocks tissue, in phase with a vertical visceral mode, and a bending mode of the upper thoracic and cervical spine. A bending mode of the lumbar and lower thoracic spine was found with a pitching mode of the head in the next higher mode located close to the principal mode. The second principal resonance at about 8 Hz corresponded to pitching modes of the pelvis and a second visceral mode. When subjects changed posture from erect to slouched, the natural frequency of the entire body mode decreased, resulting in a decrease in the principal resonance frequency. Shear deformation of buttocks tissue increased in the entire body mode due to the same change of posture. The complex body motions suggest that any forces causing injury from whole-body vibration will not be well-predicted by biodynamic models incapable of representing the appropriate body motions and the effects of body posture. It seems likely that the greatest risk of back problems will arise from the bending deformations of the spine.

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More information

Published date: 12 May 1997
Keywords: Experimental modal analysis, Posture, Resonances, Whole-body vibration

Identifiers

Local EPrints ID: 429456
URI: https://eprints.soton.ac.uk/id/eprint/429456
ISSN: 0021-9290
PURE UUID: b6bd3d16-a55c-4f1b-806c-26a1246ba302
ORCID for Michael J. Griffin: ORCID iD orcid.org/0000-0003-0743-9502

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Date deposited: 27 Mar 2019 17:30
Last modified: 10 Sep 2019 00:57

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Author: Satoshi Kitazaki

University divisions

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