Lumbar spine passive stiffness correlates to peak lumbar spine angle following postural perturbations

The passive tissues of the lumbar spine have been hypothesized to be a contributing factor to the stability of the spinal column, and although this has been primarily studied under non-perturbation conditions, it has been hypothesized that passive structures may play an important role during unexpected perturbations, during which they have no neural time delay in their counter-moment production. However, it remains unknown if those with higher lumbar spine passive stiffness (LSPS) have different responses during dynamic perturbations. Therefore, the purpose of the current work was to determine if one's LSPS correlates to the maximum amount of lumbar flexion and centre of pressure excursion following an unexpected perturbation. Twenty participants completed a blinded box-drop task. Their lumbar spine angle and centre of pressure were measured, and peak lumbar spine angle and centre of pressure excursion were determined. A significant relationship was observed between the peak lumbar spine flexion angle experienced following an unexpected perturbation and the stiffness in the low (p = 0.025, R² = 0.249) and transition (p = 0.001, R² = 0.500) stiffness zones in extension. Individuals with higher LSPS experienced lower peak lumbar spine angles. No relationship was observed between LSPS and centre of pressure excursion. Results suggest that LSPS may be a stabilizing component of the lumbar spine following unexpected perturbations. However, the lack of an observable relationship between LSPS and centre of pressure excursion may suggest that LSPS is less indicative of overall postural stability following a perturbation.