Physiological extent, range and rate of muscle stretch for soleus, medial gastrocnemius and tibialis anterior in the cat.

Abstract

To provide information on the potential stresses imposed on muscle receptors by natural movements, a cinematographic analysis was undertaken of the unrestrained walking, trotting, galloping, jumping and landing movements of 11 adult cats. Appropriate lever arm measurements were also made on 50 freshly displatched cats such that instantaneous representative lengths of soleus, medial gastrocnemius and tibialis anterior could be calculated. Use was made of a previous electromyographic analysis of hind limb muscles during unrestrained locomotion (Engberg, 1964; Engberg and Lundberg, 1969) and consideration given to recordings made by Severin, Shik and Orlovskii of the discharge of dorsal and ventral root filaments supplying ankle extensors during controlled walking of the high decerebrate cat (1967a and b). This approach revealed that locomotor movements involve 3 basic patterns of muscle displacement for the ankle extensors: a large near-static stretch that is alpha-gamma passive (as occurs in crouching); a large dynamic stretch that is also alpha-gamma passive (as occurs in the F phase of the step and after launch-off in the jump); and another dynamic stretch which involves co-activation of alpha and gamma systems and becomes extensive with an increase in forward speed (as occurs in the E2 phase of the step and during landing). There is discussion of the simulation of locomotor type stretch for ankle extensors and the more complex behaviour of tibialis anterior.