Connie Hsu, Harvard College ‘16
Eric Castillo, and Daniel Lieberman, Department of Human Evolutionary Biology, Harvard University

Abstract

This study tests the hypothesis that there is an underlying tradeoff between strength of the Rectus Abdominus and back (Erector Spinae, Multifidus, Quadratus Lumborum, or Psoas) muscle strength, which leads to variations in lumbar lordosis. The study also tests the hypothesis that lumbar lordodsis is associated with decreased rostral (back) disc height. A sample of magnetic resonance image (MRI) scans from healthy, young adult volunteers were analyzed to investigate factors affecting lumbar lordosis variations. In contrast to previous studies that found an association between lumbar extensor muscle volume lumbar lordosis (Meakin et al., 2013), we hypothesize that lumbar lordosis will covary with the relative strength of agonist-antagonist trunk muscle groups. Thus, we predict that subjects with larger, and thus stronger, Rectus Abdominis muscles relative to lumbar extensor muscles have decreased lumbar curvature in the lower back due to the antagonistic role of the Rectus Abdominis in lower back movement (flexion, instead of extension). We also expect that subjects with larger lumbar extensors relative to trunk flexors will show increased lumbar curvature. In addition to trunk strength, we also test the hypothesis that soft-tissue factors, such as increased posterior wedging of the vertebral discs (as indicated from the rostral (back) disc height relative to the max disc height of that level) will be positively associated with an increased lumbar curvature. Testing the hypothesized trade-off between hypaxial and epaxial trunk strength in the lordotic spine will lead to a better understanding of how stability and range of motion interact to moderate variations in lumbar lordosis, which has important implications for the intervention and prevention of biomechanical risk factors for back pain.

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