Changes in the mechanical properties and pressure pain thresholds of muscles in patients with fibromyalgia and their relationship with clinical parameters: a case-control study

PURPOSE: The association between fibromyalgia and changes in muscle mechanical properties is unclear. The primary objective of this study was to compare the mechanical properties (tone, stiffness, and elasticity) of the upper trapezius (UT), extensor carpi radialis brevis (ECRB), and medial gastrocnemius (MG) muscles between patients with fibromyalgia (PwFM) and healthy controls. The secondary objective was to investigate the association between muscle mechanical properties and relevant clinical parameters. METHODS: ), pain intensity using a visual analog scale, and disease impact using the Revised Fibromyalgia Impact Questionnaire. RESULTS: Muscle frequency (tone) and dynamic stiffness in the UT, ECRB, and MG were significantly higher in the PwFM group compared to controls (p < 0.05). Effect sizes were strong for the UT (|r|≥0.5), weak to moderate for the ECRB (|r|=0.293-0.306), and weak for the MG (|r|=0.293). No significant between-group differences were observed in logarithmic decrement (elasticity) (p > 0.05). In the PwFM group, a moderate positive correlation was found between the frequency of the MG muscle and its PPT (r = 0.508, p = 0.003). CONCLUSION: The present study revealed that the tone and stiffness of the UT, ECRB, and MG muscles were increased in PwFM. These findings indicate that altered muscle mechanical properties were associated with fibromyalgia and may warrant consideration in future research exploring clinical management approaches.