Upside Down Labs has this neat kit on Tindie that lets you listen to your muscles!
BioAmp v1.5 is a single chip biopotential amplifier. It can record any biopotential signal non-invasively and doesn’t require any microcontroller to sample the signal. You just plug 9v Battery to board, Electrodes to body and Audio jack to Mobile/Laptop and you are ready to record signals like EMG, ECG, EOG, and EEG. You can record the signals on a pc using audacity OR on mobile using Backyard Brain’s spike recorder app.