ACTION POTENTIALS FROM SINGLE MOTOR UNITS IN VOLUNTARY CONTRACTION

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Abstract
Action potentials in single motor units in normal human biceps and triceps muscles were recorded with concentric needle electrodes. Moderate contraction gives a simple electromyogram. Increase of contraction involves increase of impulse frequency in the individual units and accession of new units. The highest frequencies distinguishable were 19-20 per sec.; low frequencies were usually 5-7 per sec., but at threshold might be much slower and highly irregular. Individual units maintained a discharge for 20-30 min. without fatigue or substitution of units. No evidence was found of separate "tonic" and "voluntary" mechanisms in neuromuscular function.

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