Using contact microphones of some sort and/or accelerometers to measure the vibrations (sounds) muscles make as they activate. This can be used as an alternative input device, or to measure muscle health/activation. Sonomyography is largely an alternative to electromyography, which is far more commonly used for various purposes.
There are some theoretical and practical advantages to sonomyography over electromyography. Firstly, contacts for surface electromyography can be pricey, and are sensitive to changing skin conditions (i.e. sweat). They are also vulnerable to electrical interference, and measuring the small currents involved can require complicated or uncommon hardware and processing. Sonomyography is not affected by sweat, is less sensitive to placement on the body, and can be measured using any computer with a sound input fairly easily. Cheap contact mics (i.e. piezoelectric) are readily available. On the other hand, they can be vulnerable to environmental sound, and since they need the muscles to actually activate, using them as input can be tiring. Phonomyography seems much less studied.
- Portable acoustic myography – a realistic noninvasive method for assessment of muscle activity and coordination in human subjects in most home and sports settings
- Technical Report: Arm Expression Recognition using Acoustic Myography