Effect of M-wave Amplitude on Inter-evaluator Concordance and Number of Detected Innervation Zones in the Medial Gastrocnemius Using Multichannel Electromyography

Guzmán Venegas Rodrigo*, Palma Traro Felipe, Contreras Javier, Caparrós Manosalva Cristian

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The Innervation Zones (IZ) correspond to clusters of neuromuscular junctions. The traditional method of locating IZs through voluntary muscle contractions may not be feasible in individuals with motor disorders. Imposed contractions by electrostimulation are an alternative. However, there is limited evidence regarding the factors that affect inter-evaluator concordance and the number of localized IZs when using imposed contraction. The main objective of this research was to determine the effect of the amplitude of compound motor action potentials (CMAPs) containing the M-wave on inter-evaluator agreement. As a secondary objective, was investigate the effect on the number of detected IZs. Twenty-four healthy volunteers (age: 21.2 ± 1.5years, weight: 67.4 ± 13.2kg, height: 1.68 ± 0.80m) participated in the study. Electrostimulation was applied to the tibial nerve to induce contraction of the medial gastrocnemius. The IZ were identified based on the M-wave recorded through multichannel electromyography. A receiver operating characteristic (ROC) analysis was conducted to assess sensitivity and specificity in detecting the IZs. Inter-rater agreement was evaluated using a two-way mixed effects test to determine the intraclass correlation coefficients (ICC). A p-value less than 0.05 was considered statistically significant. The ROC analysis revealed that for both evaluators, a specificity of 95% was achieved with an amplitude ≥30 %. The area under the ROC curve was 0.980 [0.964, 0.996], indicating a strong influence of CMAP amplitude on detection of IZs. The highest level of agreement (ICC = 0.788 [0.713, 0.844]) among the evaluators was observed with CMAP amplitudes equal to or greater than 80 % of the maximum M-wave. The findings of this study demonstrate that both the number and the inter-evaluator concordance for detecting IZs using imposed contractions are strongly influenced by the amplitude of the M-wave. Higher M-wave amplitudes were associated with improved concordance and increased IZ detection, making it crucial to standardize amplitude settings for reliable outcomes.

Translated title of the contributionEfecto de la Amplitud de la Onda M sobre la Concordancia entre Evaluadores y el Número de Zonas de Inervación Detectadas en el Gastrocnemio Medial Mediante Electromiografía Multicanal
Original languageEnglish
Pages (from-to)1775-1780
Number of pages6
JournalInternational Journal of Morphology
Issue number6
StatePublished - 1 Dec 2023

Bibliographical note

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  • Imposed Contraction
  • Innervation Zones
  • Inter-evaluator concordance
  • M-wave
  • Medial Gastrocnemius


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