Human skeletal muscle size and architecture: variability and interdependence.

Seven hundred and eleven women and men (aged 3-94 years, including normal individuals and highly trained bodybuilders) were tested for the thickness and pennation angles of their triceps brachii (TB), vastus lateralis (VL), and gastrocnemius medialis (GM) muscles. The variations of muscle thickness and pennation angles were largest in TB (6-66 mm and 5-55 degrees), followed by VL (8-45 mm and 7-33 degrees) and GM (11-36 mm and 12-33 degrees), and women showed smaller variations than men. These results suggest the existence of muscle- and gender-specificity in the variability of muscle dimensions. Significant positive correlations were observed between muscle thickness and pennation angles (r = 0.81, 0.61, and 0.56, for TB, VL, and GM, respectively), indicating that the size-dependence of the pennation angle is a general feature of pennate muscles.