title: Determinants of mean motor unit size: impact on estimates of motor unit number.
abstract: The purpose of this study was to compare two fundamentally different methods of deriving the average surface-detected motor unit action potential (S-MUAP) size from which to calculate a motor unit number estimate (MUNE), namely: (1) the simple arithmetic average of S-MUAP parameter values; and (2) a computer-derived datapoint by datapoint average waveform which takes account of differences in S-MUAP shapes and durations. Multiple point stimulation was used to collect representative samples of between 11 and 20 S-MUAPs (mean 15 +/- 2 SD) from the median-innervated thenar muscles of 20 healthy control subjects between 20 and 76 years of age (mean 48 +/- 19 SD). The average S-MUAP size based on peak-to-peak amplitude, negative peak amplitude, and negative peak area measurements was calculated using the two different methods. The mean S-MUAP sizes based on the average waveform were significantly lower in all cases than those based on the simple average of S-MUAP parameter values. Differences tended to be greatest for MUNEs based on peak-to-peak amplitude (35%), less for negative peak amplitude (20%), and least for negative peak area (16%).
authors.affiliation: Faculty of Kinesiology, University of Western Ontario, London, Canada.
authors.forename: T J
authors.initials: TJ
authors.lastname: Doherty
authors.forename: D W
authors.initials: DW
authors.lastname: Stashuk
authors.forename: W F
authors.initials: WF
authors.lastname: Brown
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D000368:Aged; D003198:Computer Simulation; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D009046:Motor Neurons / Q000166:cytology / Q000502:physiology*; D009132:Muscles / Q000294:innervation*