Processing of electrical activity in human muscle during a gradual increase in force.

The integrated electrical activity, the number of zero crossings and the number of turns, the mean amplitude and the ratio between them, of the electrical activity were compared in the brachial biceps muscle and the anterior tibial muscle of 20 controls. The electrical activity and force were analysed every 100 msec during a gradual increase in force from zero to maximum within 10 sec. The square root of integrated electrical activity increased linearly with increasing force. The slope of this relation was inversely related to maximum force when the increasing force was expressed in kilograms. The number of zero crossings per unit time increased with increasing force up to 40-60% of maximum force after which it remained constant. Comparison of 100 microV and 50 microV level detections suggested that there is a cancellation of small spike components in the electrical activity during higher force. The square root of integrated electrical activity was linearly related to mean amplitude between turns and the number of zero crossings was linearly related to the number of turns. In conclusion the information obtained by analysis of integrated activity and number of zero crossings is probably also obtained by number of turns and mean amplitude analysis.