Ultrasound Evaluation of Muscle Thickness Changes in the External Oblique, Internal Oblique,and Transversus Abdominis Muscles Considering the Influence of Posture and Muscle Contraction

[Purpose] The aim of this study was to investigate muscle thickness changes in theexternal oblique (EO), internal oblique (IO), and transversus abdominis (TrA) musclesbetween the neutral position and trunk rotation, under a state of rest without voluntarycontractions, and isometric contractions to both sides with resistance of 50% of themaximum trunk rotation strength. [Subjects] The subjects of this study were 21 healthyyoung men. [Methods] Muscle thickness changes in the EO, IO, and TrA in each position andstate were evaluated by ultrasound. The range of motion at maximum trunk rotation and themaximum strength of trunk rotation were measured using a hand-held dynamometer. [Results]In the neutral position and at 50% trunk rotation to the right side, the thicknesses ofthe IO and TrA significantly increased with resistance. In both states, the thicknesses ofthe IO and TrA significantly increased at 50% trunk rotation to the right side.[Conclusion] The muscular contractions of the IO and TrA were stronger during ipsilateralrotation than in the neutral position and with resistance than at rest. Moreover, themuscular contraction was strongest in the resistive state during ipsilateral rotation.Key words: Trunk rotation, Low back pain, Functional evaluation