Computation of trunk equilibrium and stability in free flexion-extension movements at different velocities

B. Bazrgari, A. Shirazi-Adl, M. Trottier, P. Mathieu

Research output: Contribution to journalArticlepeer-review

60 Scopus citations


Velocity of movement has been suggested as a risk factor for low-back disorders. The effect of changes in velocity during unconstrained flexion-extension movements on muscle activations, spinal loads, base reaction forces and system stability was computed. In vivo measurements of kinematics and ground reaction forces were initially carried out on young asymptomatic subjects. The collected kinematics of three subjects representing maximum, mean and minimum lumbar rotations were subsequently used in the kinematics-driven model to compute results during the entire movements at three different velocities. Estimated spinal loads and muscle forces were significantly larger in fastest pace as compared to slower ones indicating the effect of inertial forces. Spinal stability was improved in larger trunk flexion angles and fastest movement. Partial or full flexion relaxation of global extensor muscles occurred only in slower movements. Some local lumbar muscles, especially in subjects with larger lumbar flexion and at slower paces, also demonstrated flexion relaxation. Results confirmed the crucial role of movement velocity on spinal biomechanics. Predictions also demonstrated the important role on response of the magnitude of peak lumbar rotation and its temporal variation.

Original languageEnglish
Pages (from-to)412-421
Number of pages10
JournalJournal of Biomechanics
Issue number2
StatePublished - 2008

Bibliographical note

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


  • Finite element
  • Flexion-extension
  • Kinematics
  • Muscle force
  • Spinal loads
  • Stability
  • Velocity

ASJC Scopus subject areas

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


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