Preventing lower limb injuries in the Australian Football League (AFL) is a primary focus of medical teams across the competition. A smaller cross-sectional area (CSA) of the multifidus muscle has been identified as increasing the injury risk of AFL athletes. Understanding why this is a risk factor has been largely theoretical. It has been shown that increased volume of the multifidus and lumbar erector spinae muscles is related to increased curvature in the lower lumbar spine. Identification of the relationships between the CSA of the multifidus, sagittal spinal angles, as well as CSAs of other trunk muscles could help us better understand why multifidus muscle CSA is an injury risk factor for AFL athletes.