Background: Although alterations in posture, flexibility, and motion control of the lumbar spine are associated with low back pain, the underlying interplay between genetic and environmental influences on these traits remains unclear. The aim of this study is to investigate the extent to which genetics and the environment influence lumbar lordosis, flexibility, and motion control. Design: The present cross-sectional and observational study employed the classic twin design with structural equation models. Methods: An inertial measurement unit with a wireless movement analysis system, the ViMove (DorsaVi, Melbourne, Australia) was used to measure lumbar lordosis, flexibility, and motion control during range of motion and functional tests. Intraclass correlation was used to determine twin resemblance for the traits. Heritability (genetic influence on trait variation) of lumbar lordosis, flexibility and motion control was estimated from 52 healthy twins, 34 monozygotic and 18 dizygotic using age and sex adjusted univariate genetic models. Results: A strong heritability estimate was found in lumbar lordosis (77%, 95% confidence interval [CI]: 38%���91%) in standing, followed by lumbar flexibility (67%, 95% CI: 32%���85%) in the sagittal plane. No significant intraclass correlations were found in monozygotic twin pairs for lumbar motion control or in dizygotic twin pairs during the hurdle step and in-line lunge test. Conclusion: Genetic factors appear to have a substantial influence on lumbar lordosis and lumbar sagittal flexibility. Lumbar motion control may be more influenced by environmental factors.