Differential kinetics of fast and slow ankle extensors during the paw-shake in the cat

Force, length, and EMG were assessed in the medial gastrocnemius and soleus muscles of two cats during the paw-shake response. The medial gastrocnemius produced high forces and significant electrical activity while force production and electrical activity were negligible in the soleus. This observation is significant as it provides evidence, through the direct measurement of muscle force, of selective recruitment of a fast muscle when a slow synergist is not activated. Additionally, the relationship among force, length, and neural activation indicates that the role of the medial gastrocnemius during the paw-shake response is to decelerate muscle lengthening and begin muscle shortening.