  The electrical activity of external anal sphincter can be registered with
surface electromyography. This signals are known to be highly complex and
nonlinear. This work aims in characterisation of the information carried in the
signals by harvesting the concept of information entropy. We will focus of two
classical measures of the complexity. Firstly the Shannon entropy is addressed.
It is related to the probability spectrum of the possible states. Secondly the
Spectral entropy is described, as a simple frequency-domain analog of the
time-domain Shannon characteristics. We discuss the power spectra for separate
time scales and present the characteristics which can represent the dynamics of
electrical activity of this specific muscle group. We find that the rest and
maximum contraction states represent rather different spectral characteristic
of entropy, with close-to-normal contraction and negatively skewed rest state.
