Repeated single fiber recordings do not affect the jitter and the fiber density

The temporal variation of at least two muscle fibers of the same motor unit was recorded with the single fiber EMG technique (SFEMG) by means of special needles and filter settings. In the normal musculus extensor digitorum communis (EDC) the mean variation (jitter) is not longer than 37 microseconds, the fiber density not higher than 1.7 fibers in a 10 ms window. To determine whether these parameters are affected by repeated SFEMG recordings, we measured jitter and fiber density in 20 fiber pairs in the left extensor digitorum communis muscle on day 0, 3, 6, 9 and 30 in 5 healthy volunteers. The mean jitter and the fiber density did not change significantly from day 0 (30.1 +/- 3.6 microseconds; 1.4 +/- 0.07) to day 30 (34.5 +/- 2.7 microseconds; 1.6 +/- 0.13). We conclude that repeated SFEMG recordings do not influence jitter and fiber density.