Seated whole body vibrations with high-magnitude accelerations-relative roles of inertia and muscle forces

B. Bazrgari, A. Shirazi-Adl, M. Kasra

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


Reliable computation of spinal loads and trunk stability under whole body vibrations with high acceleration contents requires accurate estimation of trunk muscle activities that are often overlooked in existing biodynamic models. A finite element model of the spine that accounts for nonlinear load- and direction-dependent properties of lumbar segments, complex geometry and musculature of the spine, and dynamic characteristics of the trunk was used in our iterative kinematics-driven approach to predict trunk biodynamics in measured vehicle's seat vibrations with shock contents of about 4 g (g: gravity acceleration of 9.8 m/s2) at frequencies of about 4 and 20 Hz. Muscle forces, spinal loads and trunk stability were evaluated for two lumbar postures (erect and flexed) with and without coactivity in abdominal muscles. Estimated peak spinal loads were substantially larger under 4 Hz excitation frequency as compared to 20 Hz with the contribution of muscle forces exceeding that of inertial forces. Flattening of the lumbar lordosis from an erect to a flexed posture and antagonistic coactivity in abdominal muscles, both noticeably increased forces on the spine while substantially improving trunk stability. Our predictions clearly demonstrated the significant role of muscles in trunk biodynamics and associated risk of back injuries. High-magnitude accelerations in seat vibration, especially at near-resonant frequency, expose the vertebral column to large forces and high risk of injury by significantly increasing muscle activities in response to equilibrium and stability demands.

Original languageEnglish
Pages (from-to)2639-2646
Number of pages8
JournalJournal of Biomechanics
Issue number12
StatePublished - Aug 28 2008

Bibliographical note

Funding Information:
This work was supported by grants from the NSERC-Canada and the Aga Khan Foundation.


  • Finite elements
  • Muscle force
  • Shock
  • Spinal loads
  • Stability
  • Whole body vibration

ASJC Scopus subject areas

  • Biophysics
  • Biomedical Engineering
  • Orthopedics and Sports Medicine
  • Rehabilitation


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