An unreported, distinctive type of increased insertional activity

A previously unreported type of increased insertional activity, referred to as "Snap, Crackle, Pop" (SCP) because of its distinctive sound, is described. It consists of trains of potentials, of varying length, which follow normal insertional activity; the individual components of each train characteristically vary in amplitude, wave form, and interpotential interval. Earlier investigation showed that SCP is not artifact, and that it is associated with normal muscle biopsies. A retrospective search of 1,047 electromyographic studies was performed to yield 50 patients with SCP. Although the overall prevalence was 5%, SCP was seen 4 times more often in male than in female patients, and was most common in young, usually muscular, males. It was found more often in leg than arm muscles and was seen with the highest frequency in the medial gastrocnemius. It has no apparent clinical significance in itself, but SCP may be mistaken for more significant types of increased insertional activity.