ABSTRACT
Recording electromyographic activity (EMG) in human subjects is rather straightforward: apply one Ag-AgCl surface electrode over the muscle belly, another closer to the tendon, amplify and filter the signal and get the subject to do his or her thing. Modem EMG amplifiers are ‘differential’, in that the two inputs are electronically subtracted from each other, resulting in high ‘common-mode’ rejection. An important consideration for human studies is that the amplifiers need to be electrically isolated from the mains power supply to avoid the risk of electric shock. Recording from many active motor units during a contraction has been likened to listening to the overall level of conversation in a people-packed room with an omnidirectional microphone; to listen in on one person’s voice a close focal microphone is required. Depending on the intensity of the contraction the electrodes generally pick up the electrical signals of a few or many motor units.
