The Influence of Lumbar Spine Passive Stiffness on Spinal Mechanical Stability: Applications of Lumbopelvic Angle Sway.

Lumbar spine passive stiffness (LSPS) has been theorized to be a necessary source of stability for the vertebral column. However, the degree that LSPS plays in maintaining spinal stability has yet to be investigated. Trunk moment of inertia has been linked to LSPS, suggesting that an optimal LSPS value may exist. Determining trunk moment of inertia and LSPS allows the trunk to be modeled as an oscillatory system. Therefore, the current work aimed to determine if LSPS can be applied to infer spinal stability by comparing the predicted natural frequency of the trunk to the mean power frequency of lumbopelvic sway. Twenty participants completed a 5-minute standing trial. The mean power frequency of their lumbopelvic angle sway was quantified using a Fourier transform. The natural frequency of the trunk was estimated using anthropometric measures. A significant relationship was observed between the natural frequency of lumbopelvic angle sway and the natural frequency of the trunk, suggesting that trunk kinematics can be modeled using inputs of LSPS and trunk moment of inertia. Such findings reinforce the importance of LSPS in maintaining the stability of the spine and provide a novel avenue for spinal stability to be investigated.