DOUBLE DISCHARGES IN HUMAN MOTOR UNITS

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Abstract
Electromyograms indicate that the temporal and voltage pattern of a motor unit remains reasonably constant and characteristic when the electrode placement remains unchanged. Double discharges of single units were recorded. Single units were activated by mild, steady, voluntary contraction or by light pin scratches on the skin. Abrupt voluntary twitches were carefully avoided. The double beats have the following characteristics: The time interval between the 2 beats ranges from 3 to 20. msec, although "couples" at intervals greater than 20. msec, are seen: they usually occur as the unit starts, occasionally as it stops and, at times, are interspersed with single beats; long strings of doubles often continue after a skin stimulus is withdrawn and in the absence of surges of voluntary effort; the time interval between 2 beats varies in a series of doubles; double discharges have lower frequency limits than singles.