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Aim:To compare the electromyographic activity and the asymmetry index among degrees of severity of temporomandibular disorders (TMD). Methods: Surface electromyography (EMG) of the right and left masseter and temporalis muscles was performed in 126 undergraduate students at rest and at maximal voluntary contraction. Three measurements were performed for five seconds of maximal contraction and mandibular rest. The degree of temporomandibular dysfunction was identified according to the Fonseca anamnestic index. The analysis of the asymmetry index for two pairs of muscles during maximal voluntary contraction was based on the asymmetry index proposed by Naeije, McCarrol and Weijs (1989). Results: 48.41% of the sample had mild TMD, followed by volunteers without TMD (26.98%), moderate TMD (19.05%) and severe (5.56%). The survey results show absence of correlation between the Fonseca anamnestic index and electromyographic activity at rest and at maximal voluntary contraction in undergraduate students in both muscles (p>0.05) and the asymmetry index did not differ between the analyzed groups. Conclusions: For the population of undergraduate students, there is no evidence that the presence and severity of TMD influence the EMG activity of masseter and temporalis muscles and the muscle asymmetry index at rest and maximal voluntary contraction.

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Background Causal mediation analysis is one way to bridge this gap by exploring the causal pathways of a given intervention. The aim of this study was to assess whether scapular motion, position, and periscapular muscle strength are mediators for pain and shoulder disability outcomes following a scapular stabilization intervention for patients with subacromial pain syndrome. Methods Sixty patients were randomized into two groups: scapular stabilization or periscapular strengthening exercises. The intervention consisted of three sessions per week for 8 weeks. The primary outcome measures were pain and disability and the following outcome measures were considered as potential mediators: scapular motion, scapular position, periscapular muscle strength, age, duration of symptoms, and side of the complaint. A model-based inference approach with bootstrap simulations was used to estimate the average causal mediation effect, average direct effect, and the average total effect from the data of a randomized clinical trial that evaluated the effect of adding scapular stabilization exercises to a scapulothoracic strengthening program in people with subacromial pain syndrome. Results The results demonstrated that none of the putative mediators were influenced by the intervention. However, muscle strength of serratus anterior, upper, middle, and lower trapezius muscles was associated with shoulder disability. Conclusion Scapular kinematic and periscapular muscle strength did not mediate the effect of scapular stabilization exercises on shoulder pain or disability scores in subjects with subacromial pain syndrome. Muscle strength of serratus anterior, upper, middle and lower trapezius were associated with shoulder disability scores at 8-weeks follow-up.