Topographical mapping of surface EMG amplitude in subjects with myofascial trigger points in the upper trapezius muscle

Barbero, Marco and Falla, Deborah and Mafodda, Luca and Cescon, Corrado and Gatti, Roberto (2014) Topographical mapping of surface EMG amplitude in subjects with myofascial trigger points in the upper trapezius muscle. In: Proceedings of the XX Congress of the International Society of Electrophysiology and Kinesiology, 14-18 July 2014, Rome, Italy.

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Abstract

AIM: This study applied topographical mapping of upper trapezius (UT) surface EMG amplitude to evaluate the location of the peak EMG amplitude in subjects with myofascial trigger points (MTrPs) within the UT muscle and healthy subjects. METHODS: Thirteen subjects with MTrP in the UT muscle and 12 healthy subjects participated. Surface EMG was recorded from the UT using a matrix of 64 electrodes aligned with an anatomical landmark system (ALS). Each subject completed a shoulder elevation task consisting of a series of six ramp contractions at 15% or 60% MVC each lasting 30s. Surface EMG signals were divided in epochs of 1s and topographical maps of the EMG average rectified value (ARV) were computed for each epoch. The EMG peak amplitude was identified for each epoch and its location with respect to the ALS was assessed during the ramped contractions. RESULTS: The location of the peak EMG amplitude in subjects with MTrP was -0.32 ± 1.2 mm at 15% MVC and -0.35± 0.9 mm at 60% MVC relative to the ALS whereas in healthy subjects, the peak EMG amplitude was 1.0 ± 1.3 mm at 15% MVC and 1.3 ± 1.1 mm relative to the ALS (difference between groups: P<0.05). The difference between the exerted force and the target force was higher in subjects with MTrP during the 60% MVC ramped contraction. CONCLUSION: Subjects with MTrPs displayed a different spatial distribution of the EMG amplitude over the UT muscle during a task of shoulder elevation. The peak amplitude of the surface EMG was located more caudally in subjects with MTrP compared to healthy subjects. Furthermore, subjects with MTrP showed reduced force accuracy during the 60% MVC ramped contractions.

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