Figure 1: Representative model-predicted force response to chirp-length perturbation for a control-rat fiber (i.e., cTnCWT fiber). (a) Total force response that includes force components due to low-frequency XB recruitment component, , and high-frequency XB distortion component, . (b) Force response due to low-frequency XB recruitment component, . (c) Force response due to high-frequency XB distortion component, . and represent stiffness magnitudes that scale the contributions of recruitment and distortion components to total stiffness. and are variables that describe the dynamic changes in the XB recruitment and distortion components due to changes in muscle length. Two chirps were administered to emphasize low- and high-frequency components of the force response: from 0.1 to 4 Hz over 40 s in chirp 1 and from 1 to 40 Hz over 5 s in chirp 2.