Motor Unit Action Potential Duration, I: Variability of Manual and Automatic Measurements

Abstract

The aim of this work is to analyze the variability in manual measurements of motor unit action potential (MUAP) duration and to evaluate the effectiveness of well-known algorithms for automatic measurement. Two electromyographists carried out three independent duration measurements of a set of 240 MUAPs. The intraexaminer and interexaminer variabilities were analyzed by means of the Gage Reproducibility and Repeatability method. The mean of the three closest manually marked positions was considered the gold standard of the duration markers positions (GSP). The results of four well-known automatic methods for estimating MUAP duration were compared to the GSP. Manual measurements of duration showed a lot of variability, with the combined intraoperator and interoperator variability greater than 30%. The greatest difference between manual positions was 11.2 ms. The mean differences between the GSP and those obtained with the four automatic methods ranged between 0.6 and 8.5 ms. Both manual and automatic measurements of MUAP duration show a high degree of variability. More precise methods are needed to improve the accuracy and reliability of the estimates of this parameter.

Reliability of quantitative EMG analysis of the extensor carpi radialis muscle

“…Algorithms used to automatically measure MUP duration are based on amplitude and slope criteria, but because of variable amounts of background noise, the algorithms have low stability and visual inspection and manual marker adjustments are often required (Bischoff et al, 1994;Stalberg et al, 1995;Takehara et al, 2004b). Previous studies have shown low reliability in manual placement of duration markers and therefore manual corrections do not guarantee reliable estimates of MUP duration (Chu et al, 2003;Nandedkar et al, 1988;Rodriguez et al, 2007;Stalberg et al, 1986;Takehara et al, 2004a). In a study conducted by Rodriquez et al (Rodriguez et al, 2007) where the variability between two experienced electromyographers in manual measurements of MUP duration using four automated methods was examined, significant differences within electromyographers and between electromyographers were found in the tibialis anterior (TA) muscle but not in the FDI.…”

Motor Unit Action Potential Duration: Measurement and Significance

“…The accuracy of CAMs has been systematically assessed in normal and pathological MUAPs [42] [45]. Comparing the GSPs (determined by means of the probabilistic method referred above) with the marker positions obtained with CAMs ( Figure 9), mean differences of up to 8.5 ms were found, with the T1 CAM.…”

“…In another study, for a systematic quantitative estimation of the intra-and inter-examiner variability in MUAP duration measurements, the Gage Reproducibility and Repeatability (Gage R&R) method [40,41] was applied [42]. This method is based on the analysis of the variance of repeated measurements of a given feature, and it is currently applied in industrial quality control studies.…”

“…Since, as a result of the conceptual and operational limitations exposed above, no single manual measurement can be accepted as the true and exact one, a probabilistic approach to the definition of the GSP has been proposed [42]. For the start or end point of a given MUAP, the GSP was calculated from a set of six marker positions obtained from the repeated marker placements made by two examiners.…”

“…The five differences between the six position values were obtained (d1 to d5) and the means between two consecutive differences were calculated ( 1 x to 4 x ). The smallest of the four mean values was selected ( 1 x in this example) and the GSP (marked with a cross in the figure) was obtained as the mean of the three manual markers with lowest mean difference (markers 1, 2 and 3 in this example) [42]. By means of this approximation, although a position cannot be assumed to be "true" or even "the best", it can be regarded as a "most likely" position.…”