The dynamic response model of nine different skeletal muscles

The frequency response model of nine different skeletal muscles in the hindlimb of the cat was determined with the aid of electrical nerve stimulation, which allows orderly stimulation of motor units concurrently with firing rate increase. It was shown that the general model consists of a linear second-order system with double real poles and a pure time delay. The pole values were different for the different muscles, ranging from 1.55 to 2.8 Hz. Similarly, the pure time delay varied from muscle to muscle, ranging from 8 to 17 ms. Statistical analysis demonstrates that, under isometric contraction with force oscillations in the range of 10-90% of maximal, the model poles are determined, and could be predicted, from the muscle´s functional and anatomical location in the limb and from its pennation pattern.