Tension responses of muscle to n-step pseudo-random length reversals: a frequency domain representation.

A high resolution, time efficient method is described for determining the complex modulus of activated striated muscle. In this method the applied oscillation of muscle length takes the form of pseudo-random binary noise, PRBN. As a time-domain signal, PRBN is an extension of the double step approach to include n steps; as a frequency-domain signal, PRBN has the properties of quasi-white noise. Fourier analysis of the PRBN length oscillations and the resulting interrupted tension transients gives rise to the complex modulus values. PRBN provides a practical demonstration of the conceptual link between time and frequency domain descriptions of strain sensitive dynamics. The method is demonstrated with intact rat papillary muscle, and glycerol extracted rabbit psoas muscle.