  Muscle contraction is often detected via EMG in prosthetics. However, signal
disturbances due to electrode motions can lead to misinterpretations.
Therefore, alternative measurement approaches are desired to increase the
reliability of the results. In this work, a novel approach based on impedance
myography is proposed. By means of an equivalent circuit of a muscle, its
electrical characteristics during contractions are analyzed. In this analysis,
a new biomedical marker named the PhaseX Effect is described. This effect is
based on the specific behavior of the phase response when the muscle is
contracted and is interesting due to its high signal robustness and low signal
processing requirements. The resilience of this effect against electrode motion
is also analyzed. Measurements of the complex impedance myography spectra are
performed on the forearms of three subjects during relaxation and contraction
of the corresponding muscle. The subject measurements show the expected
behavior of the muscle model. Actual muscle contractions can easily be detected
via a simple analysis of the phase response. For a better visualization, the
measurements are repeated while acquiring a synchronized video of the moving
forearm. The particular effect of the phase response during muscle contraction
can be used as a new marker that can be beneficial in several applications such
as prostheses control. The PhaseX Effect has high reliability and low signal
processing requirements, making it advantageous over other muscle activity
markers. The combination of a reliable marker and simple signal analysis
promises to become a new method for prostheses control.
