Decoding the neural drive to muscles from the surface electromyogram.

This brief review discusses the methods used to estimate the neural drive to muscles from the surface electromyogram (EMG). Surface EMG has been classically used to infer the neural activation of muscle by associating its amplitude with the number of action potentials discharged by a population of motor neurons. Although this approach is valuable in some applications, the amplitude of the surface EMG is only a crude indicator of the neural drive to muscle. More advanced methods are now available to estimate the neural drive to muscle from the surface EMG. These approaches identify the discharge times of a few motor units by decomposing the EMG signal to determine the relative changes in neural activation. This approach is reliable in several conditions and muscles for isometric contractions of moderate force, but is limited to the few superficial units that can be identified in the recordings.