Comparison of MF and RMS EMG parameters in women with TMD and asymptomatic women during sustained bilateral...

Muscle fatigue is characterized by a reduction in the muscle's ability to generate force during voluntary contractions and can be assessed using surface electromyography (EMG) through the parameters of median frequency (MF) and root mean square (RMS).

This study aimed to compare the Median Frequency (MF) and Root Mean Square (RMS) values of the masseter and anterior temporalis muscles between women diagnosed with myogenic Temporomandibular Disorder (TMD) and asymptomatic women during a sustained submaximal bilateral bite task on the molars.

This cross-sectional study included 86 women, distributed into TMD and Control groups based on DC/TMD diagnosis. The angulation coefficient (β) of the linear regression line of the RMS and MF was evaluated in the submaximal bilateral molar bite task at 50% of the maximum bite force for 30 s.

A negative intragroup β coefficient was observed for MF in all muscles in both groups (p < 0.001 for all), indicating a decline in MF over time. A positive intragroup β coefficient was observed for RMS in all muscles in both groups, indicating an increase in RMS over time. The Control Group showed a significantly greater negative β coefficient for MF in the right masseter (p = 0.01) and left masseter (p = 0.01) muscles, indicating a steeper decline in MF during the fatigue protocol, and a significantly greater positive β coefficient for RMS in the left anterior temporalis muscle (p = 0.01), indicating a steeper increase in RMS, compared to the TMD Group.

The long-duration submaximal bite task produced signs of muscle fatigue in both groups; however, signs of fatigue were significantly more pronounced in the Control Group, specifically in the masseter muscles (MF decline) and the left anterior temporalis muscle (RMS increase), challenging our initial hypothesis of greater fatigue in the myogenic TMD Group.