Factors contributing to lumbar region passive tissue characteristics in people with and people without low back pain

Background: Previously, we demonstrated that people in the Rotation with Extension low back pain subgroup display greater asymmetry of passive tissue characteristics during trunk lateral bending than people without low back pain. The purpose of this secondary analysis is to examine factors that explain the group differences. Methods: Twenty-two people in the Rotation with Extension subgroup, and 19 people without low back pain were examined. Torque, lumbar region kinematics, and trunk muscle activity were measured during passive and isometric resisted trunk lateral bending. The dependent variables were lumbar region passive elastic energy to each side; the independent variables included group, gender, anthropometrics, trunk muscle characteristics, and an interaction factor of group and trunk muscle characteristics. Multiple linear regression was used for the analysis. Findings: Anthropometrics explained passive measures to the left (P =.03). Anthropometrics (P <.01), trunk muscle characteristics (P <.01), and the interaction of group and trunk muscle characteristics (P =.01) explained passive measures to the right. After accounting for gender and anthropometrics, 43.7% of the variance in passive measures to the right was uniquely accounted for by trunk muscle characteristics for the Rotation with Extension subgroup, compared to 0.5% for the group without low back pain. Interpretation: Anthropometrics explained passive measures with trunk lateral bending to both sides, in both groups. For people in the Rotation with Extension subgroup, there was a direct relationship between trunk muscle performance and passive measures to the right. Muscle is an important contributing factor to asymmetry in this subgroup and should be considered in treatment.