Twitch characteristics in relation to muscle architecture and actual muscle length.

The length dependence of twitch time characteristics is quantified for several skeletal muscles of the rat: lateral gastrocnemius, medial gastrocnemius, plantaris, soleus and semimembranosus. It is shown that muscle architecture influences the length dependent behaviour of twitch time characteristics of muscles. Twitch contraction time is less susceptible to length changes of the muscles than the twitch relaxation time. With the exception of the relaxation time in the second part of the relaxation, the twitch time characteristics behave different with respect to their dependence on fibre length, in fact muscles that differ in architecture. It is concluded that twitch time characteristics are dependent on the actual muscle length and therefore should be determined at a well defined length.