Latent Myofascial Trigger Points (LMTrPs) are defined as certain pain-free hyperirritable spots in a taut band of muscle, which lead to alternation in muscle activation pattern in both loaded and unloaded conditions. Fatigue can alter the stability of the cervical spine because of transferring loads to the passive connective tissues and also increasing muscle activity. Few studies have investigated the effects of fatigue on the parameters of the upper trapezius muscle as a more common muscle to MTrPs. This study attempts to examine the electromyographic activity of the upper trapezius muscle fatigue during shoulder elevation. Materials and Methods: Thirty-six right-handed subjects without upper extremity disorders took part in this study. The highest measured force level was assumed to be the Maximal Voluntary Contraction (MVC) of the trapezius. A sustained submaximal contraction of the trapezius was performed. The subjects were asked to sustain a unilateral (80%) MVC isometric shoulder elevation until the force gauge monitor showed (50%) of MVC in at least three minutes. Results: The Root Mean Square (RMS norm) of the sustained trapezius contractions showed differences between the groups. The Myocardial Depressant Factor (MDF) parameters of the left and right sides of both healthy subjects and patients were significantly different (P<0.001). Conclusion: The increase in RMS is related to the recruitment of additional motor units and also an increased firing rate. These are necessary to compensate for the loss of force. This accumulation also inhibits the excitability of the muscle membrane, thereby causing a decrease in the firing rate and, consequently, a decrease in Median Frequency (MF).

Objectives: The purpose of this work was to explore cervical position sense and electromyographic (EMG) responses of cervical muscles during head repositioning movements in students with and without upper trapezius muscle trigger points. Materials and Methods: Forty-six right-handed men and women subjects without upper extremity disorders participated in this study. The maximal voluntary contraction (MVC) was measured three time before the fatigue test. A force gauge was used to measure force while recording with a monitor. Measurement was initiated with a MVC force before and after fatigue pain and head positioning were measured. When the protocol was accomplished, the subjects showed signs of exhaustion; however, they were not subjectively evaluated for fatigue. As the protocol aimed at assessing muscle fatigue, a force level of 80% MVC was induced. Results: These findings support the argument that the precision of the neck position sense can be reduced by the fatigue of the neck muscle. Fatigue impaired balance in the trapezius muscles. After removing vision this resulted in an increased center of pressure excursions on a force platform. Motor control did not change significantly in this study. Conclusions: Fatigue had a more significant effect on cervical kinematics in the healthy subjects, probably due to the fact that altered neck motor control in volunteers implied that these individuals were not completely able to make up for fatigue of the neck muscle. Significant pain and head positioning changes were identified following fatigue applied to the pre-determined myofascial trigger points, but the changes were insignificant in the sham control group.

Myofascial Pain Syndrome (MPS) is one of the most frequent causes of muscle pain. MPS is characterized by the presence of a myofascial trigger point (MTrP), defined as a hypersensitive spot in a taut band of a skeletal muscle that is painful to stimulation (compression, or needling), elicits a referred pain distant to the spot, and is associated with restricted range of motion. The purpose of this study was to assess the correlation between fatigue over a myofascial trigger point in the upper trapezius muscle and range of motion of the cervical spine, electromyographic activity, and pain in patients with myofascial trigger point. Methods: This is a single-blind cross-sectional study. Forty participants of both sexes, aged 18 to 35 years, with chronic neck pain and myofascial trigger points in the upper trapezius muscle were included in the study. The participants were assessed using the Numeric Rating Scale, algometry and electromyographic activity. Results: Improvement in flexion range of motion was found to be greater in interventional group compared to the control group( p<0.05). Conclusion: Fatigue applied to the interventional group can reduce pain and disability, and increase ROM in individuals with MTrP. This treatment may therefore be considered for use as an alternative method in treating MTrP.