Relationship between asymmetric trunk flexion movement and elector spinae muscle activity

[Purpose] To clarify the relationship between asymmetric trunk flexion movement and erector spinae (ES) muscle activity using a three-dimensional motion analysis system and surface electromyography. [Subjects and Methods] The subjects comprised 14 healthy individuals. Angles of trunk flexion, rotation, and side bending were measured using a three-dimensional motion analysis system attached to the trunk and pelvic segment. Activities of the ES muscle on both sides at the L1 and L4 levels were measured using surface electromyography. [Results] In healthy individuals, the ES was more markedly activated in the trunk extension phase than in the trunk flexion phase. There was no significant difference in terms of the extent of trunk rotation and trunk side bending during these tasks. [Conclusion] This study did not clarify the relationship between asymmetric movement during trunk flexion and ES activity.