New Directions in Structural Mechanics of Muscle Contraction

INTRODUCTION When a muscle shortens it must increase in transverse crosssectional area in order to minimize any changes in volume. This increase in cross-sectional area may occur as a bulging in depth or in width. Pennate muscles have structural asymmetries due to the nature of the pennation, and thus may have asymmetries between the bulging in depth or width. Muscle depth can be considered as the distance between the aponeuroses. Increases in the muscle depth cause increases to the fascicle pennation, and this reduces the fascicle shortening velocity and increases the potential for force generation and the gearing of the fascicles. The medial and lateral heads of the gastrocnemius show different bulging characteristics during contraction [1,2], and this may be reflected in differences in gearing.