Some Characteristics of the Electro-Myograms of Quick Voluntary Muscle Contractions

Abstract

The electro-myograms making up the data from which these observations are reported were obtained from oscillographic records of amplified muscle action potentials. Ten adult human subjects were used. The action potentials were picked up by modified pore electrodes 1 which were inserted into the body of the muscle to be investigated. The active electrodes were insulated from all but a small area of the interior of the muscle, allowing fair isolation of antagonistic muscles. The amplified action potentials were photographed in a Westinghouse multi-element oscillograph. Action potentials could be simultaneously photographed from 2 different sources, usually the biceps and triceps brachii of the right arm.

A simple reaction time set-up was used. The subject was instructed to extend his forearm as quickly as possible following the disappearance of the glow of a low wattage neon bulb. The arm was supported horizontally on a rest allowing free movement about the elbow. The photographs included markers showing arm movement, time in 10 sigma intervals and a marker showing when the subject was given the ready signal and the stimulus. Reaction times were read to the first action potentials after the stimulus and to the first arm movement. The records show an average of about 58 sigma lapse between the first large action potential changes and the corresponding movement of the forearm. This time is fairly constant, varying in ordinary subjects by not more than ±8 sigma. There was no evidence of a preliminary tension in either the muscle which was to be used in the response or its antagonist preceding the stimulus and related to the warning signal.