Coordination processes in a human motoneuronal pool.

: Using two leads of a multielectrode the EMG from biceps brachii muscle in man was recorded. The test-persons were ordered to produce a sustained isometric flexion force in the elbow joint which they could control optically. In the range of about 3-5% of maximum force it was possible to identify 2-5 active motor units under this condition. Cross interval histograms were calculated showing two types of coordination between two simultaneously active motor units: 1st, periods of relative phase-coordination in different extent. This means that cross-intervals are fluctuating in a small range for short time periods. An arbitrary subdivision of the fluctuation ranges and the time periods into different classes shows that about 20-35% of the total of the cross-intervals are coordinated by relative phase dependence. In these cases the ratio of the mean discharge rates is 1:1 approximately. 2nd, another type of relationship -f the motor units active at the same time we have called "frequency coordination". This means that the fluctuations of cross-intervals around the mean discharge rate ratio are smaller than the fluctuations of the discharges of both single units around their own mean value. In these cases, which are more frequent than phase-coordination (up to 50%), the ratios of the mean discharge rates are 1:1,2 and more.