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Calculation of the electromyographic jitter
  1. Jan Ekstedt2,
  2. Göran Nilsson3,
  3. Erik Stålberg
  1. Department of Neurology, University of Uppsala, Sweden
  2. Department of Clinical Neurophysiology, University of Uppsala, Sweden


    The electromyographic jitter is the variability at consecutive discharges in the time interval between two action potentials from two muscle fibres from the same motor unit. This paper deals with different methods of expressing the jitter. The method of choice seems to be Mean Consecutive Difference (MCD)

    [Formula: see text]

    where D1, D2 etc. are the individual time interval measurement data and n the number of discharges, preferably 50 or, if the jitter is not changing, 200. MCD can also be estimated from other measures of the jitter like Mean Range of Two (MR2) (giving the same estimated value as MCD), Mean Range of Five (MR5), Mean Range of Ten (MR10) and also from the Standard Deviation (SD). In a distribution without trends the following relations hold:

    MCD = 1·13×SDMCD = 0·49×MR5MCD = 0·37×MR10·

    The presence of slow variations and trends in most recordings makes SD not well suited for calculation because of the risk of getting too high estimates of the jitter.

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    • 2 Address for correspondence: Dr. Jan Ekstedt, Department of Neurology, University Hospital, S-750 14 Uppsala, Sweden.

    • 3 Present address: Pharmacia AB, Uppsala, Sweden.

    • 1 This investigation was supported by the Swedish Medical Research Council (Grant 14X-135).