MEASUREMENT OF THE TRUNK MUSCULATURE FROM T5 TO L5 USING MRI SCANS OF 15 YOUNG MALES CORRECTED FOR MUSCLE-FIBER ORIENTATION

Lumbar and thoracic transverse magnetic resonance image scans from T4 to the sacrum were collected from 15 young men at a slice thickness of 5 mm. Anatomical muscle areas and distances from muscle centroids to their respective intervertebral disc centroid were measured directly from the scans, from which physiological muscle areas and muscle moment arms, corrected for the cosine between the scan plane and dominant fibre line of action, were calculated. Only a portion of the abdominal wall, and quadratus lumborum, and lower lumbar levels of longissimus thoracis pars lumborum demonstrate changes in corrected areas and moment arm distances greater than 10% relative to their uncorrected values measured directly from scan slices. The data illustrate the changing cross-sectional areas and mechanical moment arms of the muscles spanning the lower thoracic and lumbar regions. Considerations and problems in interpretation of these cross-sectional areas and moment arms for biomechanical analyses are discussed, together with the limitations for direct application of these geometric measurements for modelling.