Electrical (or magnetic) stimulation of peripheral (motor or mixed) nerves can induce MEPs (called M-waves) in muscles innervated by the motor nerve. For example, electrical stimulation of the median nerve can induce M-waves in the muscles of the thenar eminence (APB, OP).

The M-wave is due to the direct activation of the muscle in the normal (orthodromic) direction, via motor neurons.