Dorsal muscle group area is defined as any muscle contained within the region posterior to the spine and ribs, and no more lateral than the lateral-most edges of the erector spinae muscles. CT scans were processed by the following steps using semi-automated algorithms in MATLAB v13.0. Initially, scans were labeled at each vertebral level to provide anatomical landmarks for subsequent measurements. Next, a posterior muscle line was drawn on abdominal and thoracic slices separating muscle from subcutaneous fat. Points were placed at the lateral-most clefts of the erector spinae muscle. An area was mapped out between these points, the central point of the spinal canal, and the posterior muscle line. Within this region, dorsal muscle group size was calculated based on density thresholds. Our primary measurement was the dorsal muscle group cross-sectional area at the T12 vertebral level, which is more commonly present in both thoracic and abdominal scans. Total psoas area was also measured as described in our previous work (5). This entailed using a transverse slice of L4 to outline the psoas muscles. This cross-sectional area was computed as the total psoas area. Figure 1 illustrates these analytic morphomics techniques.