Sagittal Plane Moment Arms of the Male Lumbar Region Rectus Abdominis: Upright Vs. Supine Posture

Abstract

Prior studies of torso muscle moment arms for inputs into torso biomechanical models have been derived from subjects lying supine. Recent research suggests that moment arms of the rectus abdominis increase when standing versus lying supine. The objective of this study was to quantify and compare the sagittal plane rectus abdominis moment arm from upright and supine postures. Cross-sectional MRI images from ten males in both upright and supine postures were obtained. Digitizing software was utilized to quantify the sagittal plane moment arms of the rectus abdominis muscle. The mean sagittal plane moment arms were significantly larger at each lumbar intervertebral level in the erect posture compared to the supine posture, ranging from 15.9% larger at L1/L2 to 49.3% larger at L4/L5. These findings indicate that the torso internal moment generating capability would be represented differently in biomechanical models that use data from studies where subjects were upright versus supine.