Synchronization of motor unit firings in several human muscles. 9th Int

was studied in six human muscles performing isometric constant-force contractions at 30 % of the maximal level. The myoelectric signal was detected with a quadrifilar needle electrode and was decomposed into its constituent motor-unit action-potential trains with the Precision Decomposition technique, whose accu-racy has been proven previously. 2. Synchronization was considered as the tendency of two mo-tor units to fire at fixed time intervals with respect to each other more often than would be expected if the motor units fired inde-pendently. A rigorous statistical technique was used to measure the presence of peaks in the cross-interval histogram of pairs of motor-unit action-potential trains. The location of the center of peak as well as their width and amplitude were measured. A synch index was developed to measure the percentage of firings that were synchronized. The percentage of concurrently active motor-uni