AbstractThe 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%)
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