Temporal Discrepancies in the Electromyographic Study of Rapid Movement

Abstract

Elbow flexor and extensor contraction and relaxation delays, relative to muscle action potentials are evaluated as 30-60 msec for contraction and 30-70 msec for relaxation, but with significant differences between subjects and between different muscles in the same subject. The contention that proper temporal interpretation of rapid movement EMGs is impossible without prior evaluation of the delays specific to the subject and muscles involved is supported by applying such evaluations to explain anomolies in rapid elbow movement EMGs. It is shown that apparent cocontraction of antagonist muscles may be an artifact explicable by these (subject and muscle specific) delay differences. The need for extensive study of muscle action delays is stressed.