Fig. 8

Maximal and sub-maximal force length relationship for human vastus lateralis muscle. The fascicle lengths were directly determined using ultrasound imaging while the forces were obtained making the usual assumptions discussed above. Note how the maximal and sub-maximal relationships do not scale linearly, and how optimal fascicle length, but not optimal muscle length, is about constant in this approach where the relationship was derived for sub-maximal levels of activation rather than sub-maximal levels of force. The “x” symbols on the graph indicate the optimal fascicle length for each of the maximal and submaximal levels of activation. The numbers on top of the graph ranging from 170 to 80 indicate the corresponding knee joint angles. (Adapted from [49], with permission)