Relation between whole-body and regional measures of human skeletal muscle.

BACKGROUND It is unknown whether regional measures of skeletal muscle (SM) in the thigh and abdomen accurately reflect whole-body SM mass. OBJECTIVE We aimed to determine whether thigh and abdominal SM measures reflect whole-body SM mass and, if so, which region is a stronger marker. DESIGN Whole-body and regional measures of SM were obtained by magnetic resonance imaging in a sample of 387 white men and women. RESULTS The regional SM measures, whether obtained by using a single image (midthigh or L4-L5 level) or a series of 7 consecutive images covering 31 cm (thigh or abdomen), were strongly correlated with whole-body SM (P < 0.001). Independent of sex, the thigh SM measures derived from a single image (men: R(2) = 0.77, SEE = 6.5%; women: R(2) = 0.79, SEE = 7.4%) or a series of 7 consecutive images (men: R(2) = 0.84, SEE = 5.4%; women: R(2) = 0.90, SEE = 5.1%) were stronger correlates of whole-body SM with smaller SEE values than were the abdominal SM measures (P < 0.01). However, SM in the abdomen was also a strong marker of whole-body SM, whether determined from a single image at the L4-L5 level (men: R(2) = 0.63, SEE = 8.2%; women: R(2) = 0.58, SEE = 10.4%) or from a series of images across the abdomen (men: R(2) = 0.77, SEE = 6.5%; women: R(2) = 0.70, SEE = 8.7%). CONCLUSION Although thigh measures of SM are better predictors of whole-body SM, a single image within the abdomen routinely used to estimate abdominal fat may also be a useful marker of whole-body SM.