Our purpose was to characterize shoulder muscle volume and isometric moment, as well as their relationship, for healthy middle-aged adults. Muscle volume and maximum isometric joint moment were assessed for 6 functional muscle groups of the shoulder, elbow, and wrist in 10 middle-aged adults (46–60 y, 5M, 5F). Compared with young adults, shoulder abductors composed a smaller percentage of total muscle volume (P = .0009) and there was a reduction in shoulder adductor strength relative to elbow flexors (P = .012). We observed a consistent ordering of moment-generating capacity among functional groups across subjects. Although total muscle volume spanned a 2.3-fold range, muscle volume was distributed among functional groups in a consistent manner across subjects. On average, 72% of the variation in joint moment could be explained by the corresponding functional group muscle volume. These data are useful for improved modeling of upper limb musculoskeletal performance in middle-aged subjects, and may improve computational predictions of function for this group.
Katherine R. Saul is with the Mechanical and Aerospace Engineering Department, North Carolina State University, Raleigh, NC. Meghan E. Vidt is with the Biomedical Engineering Department and Virginia Tech—Wake Forest School of Biomedical Engineering and Sciences, Wake Forest School of Medicine, Winston-Salem, NC. Garry E. Gold is with the Radiology Department, Stanford University, Stanford, CA. Wendy M. Murray is with the Departments of Biomedical Engineering & PM&R, Northwestern University, Chicago, IL.