Figure 2.

Change in muscle fascicle length with passive change in muscle–tendon length

Muscle fascicle length measured with ultrasound, as a function of muscle–tendon length calculated from ankle and knee angles, for seven fascicles from a single subject whose ankle was rotated from 66 to 100 deg with the knee flexed 80 deg. The diamonds indicate slack lengths. The muscle–tendon length (horizontal coordinate) of each diamond is the muscle–tendon length at which a fascicle falls slack (l_g(FSL)), and the muscle fascicle length (vertical coordinate) of each diamond is the fascicle slack length (l_f(FSL)).