The motor unit and electromyography--the legacy of Derek Denny-Brown.

With the development of the concept of the motor unit and new recording instruments, single motor unit action potentials (MUAPs) were recorded in 1929 in man by Adrian and Bronk and in the experimental animal by Denny-Brown. Studies of MUAPs in patients with neuromuscular disease followed, and in 1938, Denny-Brown and Pennybacker laid the foundation for clinical electromyography (EMG). Action potentials of single contracting or spontaneously firing motor units, termed fasciculations, were recorded and separated from the action potentials of single denervated muscle fibers, termed fibrillations. Thus, it was possible to interpret muscle twitching and cramping by EMG and separate neurogenic from myopathic diseases. Since then, EMG and neuromuscular disease have expanded greatly providing greater diagnostic capability and therapeutic success.