Computed tomography scans of 96 women aged between 40 and 63 years were systematically measured to determine torso muscle moment arms and cross-sectional areas at L 2L 3, L 3L 4 and L 4L 5 disc levels. The major findings were as follows: (1) the mean muscle moment arm and area data were not different bilaterally; (2) psoas, quadratus lumborum, and latissimus dorsi muscle moment arms consistently changed at the three disc levels, while erector spinae, rectus abdominis, transverse abdominis and the oblique muscles remained about the same distance from the three disc centroids; (3) psoas and quadratus lumborum muscles increased in mean size at the lower levels and (4 gross torso anthropometry and body weight had a significant (P < 0·01) but varied correlation (r(2) from 0·12 to 0·65) with the size of the erector spinae and psoas muscles, and with the moment arms of the rectus abdominis, transverse abdominis, latissimus dorsi, and oblique muscles.

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