  Surface electromyography (sEMG) is a widely used muscle activity monitoring
technique. sEMG measures muscle activity through monopolar and bipolar,
multi-electrode electrodes. The surface electrodes are placed on the surface of
the skin above the target muscle and the received signal can be used to infer
the state of the muscle - active, inactive or fatigued - which serves as vital
information during neurological and orthopaedic rehabilitation. Additionally,
the sEMG signal can also be used for the control of prostheses. sEMG requires
contact with the participant's skin and is thus a potentially uncomfortable
method for the measurement of muscle activity. Moreover, the setup procedure
has been termed time-consuming by sEMG experts and is listed as one of the main
barriers to the clinical employment of the technique. Previous studies have
shown that architectural changes, particularly muscle deformation, can provide
information about the activity of the muscle, providing an alternative to sEMG.
In all these studies, the muscle deformation signal is acquired using
ultrasound imaging, an approach known as sonomyography (SMG). Despite its
advantages, such as improved spatial resolution, SMG is still a contact based
approach. In this paper, we propose a non-contact muscle activity monitoring
approach that measures the muscle deformation signal using a Frequency
Modulated Continuous Wave (FMCW) mmWave radar which we call radiomyography
(RMG). In future, this system will enable muscle activation to be measured in
an unconstrained and less cumbersome manner for both the person conducting the
test and the individual being tested.
