Female and male trunk geometry: size and prediction of the spine loading trunk muscles derived from MRI

Objective. Develop a gender specific database of trunk muscle cross-section al areas across multiple levels of the thoracic and lumbar spine and develo p prediction equations for the physiological cross-sectional area as a func tion of gender and anthropometry. Design. This study quantified trunk muscle cross-sectional areas of male an d female spine loading muscles. Background. There is a lack of comprehensive data regarding the female spin e loading muscle size. Although biomechanical models often assume females a re the same as males, little is known regarding gender differences in terms of trunk muscle areas and no data exist regarding the prediction of trunk muscle physiological cross-sectional areas from commonly used external anth ropometric measures. Methods. Magnetic resonance imaging scans through the vertebral bodies from Tg through SI were performed on 20 females and 10 males. Muscle fiber angl e corrected cross-sectional areas were recorded at each vertebral level. Li near regression techniques taking into account anthropometric measures were utilized to develop prediction equations for the physiological cross-secti onal area for each muscle of interest, as well as tests for differences in cross-sectional areas due to gender and side of the body. Results. Significant gender differences were observed for the prediction of the erector spinae, internal and external obliques, psoas major and quadra tus lumborum physiological cross-sectional areas. Anthropometric measures a bout the xyphoid process and combinations of height and weight resulted in better predictions of cross-sectional areas than when using traditional ant hropometry. Conclusions. This study demonstrates that the trunk muscle geometry of fema les and males are different, and that these differences should be considere d in the development of biomechanical models of the torso. Relevance The prediction of physiological cross-sectional areas from extern al anthropometric measures provide gender specific equations to assist in e stimation of forces of muscles which load the spine for biomechanical purpo ses. (C) 2001 Elsevier Science Ltd. All rights reserved.