JOSEPHSON, Robert K.; SYME, Douglas A.: How to build fast muscles. II. Asynchronous muscle–a design breakthrough

Some but not all flight and sound-producing muscles in insects contract in an oscillatory manner if they are activated by neural input and attached to a mechanically-resonant load. The frequency of the oscillations is the resonant frequency of the load, and is relatively independent of the frequency of the neural activity that activates the muscle. Such muscles are described as asynchronous, because there is not a direct correspondence between muscle contraction and the electrical potential changes initiated by neural input. The features of asynchronous muscle that allow oscillatory contraction are delayed shortening deactivation and delayed stretch activation. Asynchronous muscles achieve high-frequency contractions without high-frequency release and removal of calcium, without hypertrophy of intracellular calcium control systems, and without unusually high cross bridge rate constants that are characteristic of high-frequency, synchronous muscles. Consequently, high-frequency asynchronous muscles have greater power output and are more efficient than are high-frequency synchronous muscles.