AIM: To apply topographical mapping of the electromyography (EMG) amplitude recorded from the upper trapezius muscle to evaluate the distribution of activity and the location of peak activity during a shoulder elevation task in participants with and without myofascial pain and trigger points (MTrP) and compare this location with the site of the MTrP.
MATERIALS AND METHODS: Thirteen participants with myofascial pain and MTrP in the upper trapezius muscle and 12 asymptomatic participants participated. High-density surface EMG was recorded from the upper trapezius muscle using a matrix of 64 surface electrodes aligned with an anatomic landmark system (ALS). Each participant performed a shoulder elevation task consisting of a series of 30▒s ramped contractions to 15% or 60% of their maximal voluntary contraction (MVC) force. Topographical maps of the EMG average rectified value were computed and the peak EMG amplitude during the ramped contractions was identified and its location determined with respect to the ALS. The location of the MTrP was also determined relative to the ALS and Spearman correlation coefficients were used to examine the relationship between MTrP and peak EMG amplitude location.
RESULTS: The location of the peak EMG amplitude was significantly (P<0.05) different between groups (participants with pain/MTrP: -0.32±1.2▒cm at 15% MVC and -0.35±0.9▒cm at 60% MVC relative to the ALS; asymptomatic participants: 1.0±1.3▒cm at 15% MVC and 1.3±1.1▒cm relative to the ALS). However, no correlation was observed between the position of the MTrP and peak EMG amplitude during the ramped contractions at either force level (15%: rs=0.039, P=0.9; 60%: rs=-0.087, P=0.778).
CONCLUSIONS: People with myofascial pain and MTrP displayed a caudal shift of the distribution of upper trapezius muscle activity compared with asymptomatic individuals during a submaximal shoulder elevation task. However, for the first time, we show that the location of peak muscle activity is not associated with the location of MTrP.
- myofascial trigger points
- high-density surface electromyography
- topographical maps
- upper trapezius muscle
- ramped isometric contractions