Toward Noncontact Muscle Activity Estimation Using FMCW Radar

Surface electromyography (sEMG) and ultrasound-based sonomyography (SMG) are established muscle activity monitoring techniques. However, both modalities require contact with the skin and are thus potentially uncomfortable and time-consuming to use. In this article, we propose a novel noncontact muscle activity monitoring approach that measures the muscle deformation signal using a frequency-modulated continuous wave (FMCW) mmWave radar which we call radiomyography (RMG). The RMG signal is a specific sequence of phase samples in the radar return, obtained through a series of operations: range bin selection, dc offset correction, arctangent demodulation, and phase unwrapping. We find that the RMG signal highly correlates with the sEMG signal across time, making RMG a reliable method for monitoring muscle activity. We also establish that our signal contains some characteristic features of the muscle deformation signal that are well known in biomechanics. Our main contribution is the proposal, development, and proof-of-concept usage of a novel noncontact muscle activity monitoring approach. This opens muscle activity monitoring up for use in rehabilitation, high-intensity contact sports analytics, performance arts, remote health monitoring, and wildlife healthcare and research. To the best of the authors’ knowledge, our approach is the first to measure the characteristic dimensional changes of muscles in vivo and without contact.