Transversus abdominis and multifidus asymmetry in runners measured by MRI: a cross-sectional study

ObjectiveThe transversus abdominis muscle (TrA) is active during running as a secondary respiratory muscle and acts, together with the multifidus, as trunk stabiliser. The purpose of this study was to determine size and symmetry of TrA and multifidus muscles at rest and with contraction in endurance runners without low back pain.DesignCross-sectional study.SettingA medical imaging centre in Melbourne, Australia.ParticipantsThirty middle-aged (43years±7) endurance-trained male (n=18) and female (n=12) runners without current or history of low back pain.Outcome measuresMRI at rest and with the core engaged. The TrA and multifidus muscles were measured for thickness and length (TrA) and antero…