Purpose: The goal of this study was to assess differences in low back stabilization and underlying mechanisms between patients with low back pain (LBP) and healthy controls. It has been hypothesized that inadequate trunk stabilization could contribute to LBP through high tissue strains and/or impingement. Evidence to support this is inconsistent, and not all methods that have been used to study trunk stabilization are equally suitable. We have recently developed a method to assess intrinsic and reflexive contributions to trunk stabilization, which aims to circumvent the limitations of previous studies.
Methods: Forty-nine participants suffering from chronic LBP and a control group of fifty healthy subjects participated in this study. Trunk stabilization was measured using force-controlled perturbations directly applied to the trunk. The actuator displacement and contact force between the actuator and subject were measured as well as electromyography (EMG) of the M. Longissimus. Underlying mechanisms were characterized using system identification.
Results: LBP patients showed lower admittance, i.e., less displacement per unit of force applied, mainly due to higher position, velocity and acceleration feedback gains. Among patients, lower trunk admittance and higher reflex gains were associated with more negative pain-related cognitions.
Conclusion: Trunk stabilization differs between LBP patients and controls, with the same perturbations causing less trunk movement in patients, due to stronger reflexes. We interpret these changes as reflecting protective behavior. These slides can be retrieved under Electronic Supplementary Material.
Keywords: Low back pain; Pain-related cognitions; Reflex; Stability; Stiffness.