A proposal to monitor muscle contraction through the change of electrical impedance inside a muscle

Dynamically monitoring muscle contraction is an important task in sports training and rehabilitation programs. Internal muscles monitoring are specially challenging because they cannot be accessed by palpation or surface EMG. It is well known that blood flow through skeletal muscle can increase 15-to 25-fold during extreme exercise compared to its rest state. Additionally, at rest, some muscle capillaries have little or no blood flowing, but during strenuous exercise, all the capillaries open. With regard to electrical properties, blood resistivity is about half of muscle resistivity. Thus, global muscle resistivity have a tendency to change when it goes from rest to activity state. Recent results suggest that resistivity changes are related to contraction rate. Bearing that in mind, Electrical Impedance Tomography turns out to be an interesting signal to monitor muscle contraction by sensing resistivity changes related to muscle activity. If low intensity current is injected and electric potentials are measured through electrodes attached on skin, resistivity maps can be obtained using this data to solve an ill-posed inverse problem. In this work the electrical impedance was measured while a muscle was under repetitive contractions. Significant changes of electrical impedance were found in the frequency of contractions.