Analysis of muscle architecture variables and their relationship with functional capacity in patients with fibromyalgia: A cross-sectional study.

BACKGROUND: Fibromyalgia (FM) is a chronic syndrome characterised by widespread musculoskeletal pain, accompanied by fatigue, functional alterations, and changes in body composition. OBJECTIVE: The main objective was to analyse muscle architecture variables using ultrasound in patients with FM. DESIGN: A cross-sectional observational study conducted in accordance with the STROBE guideline. METHODS: 80 patients with FM (54.06 ± 9.66 years) were assessed. Sociodemographic and anthropometric variables, functional capacity (5-sit-to-stand-test (STST), Handgrip (HGS), Time Up Go (TUG) and 4- metres-walk-test (4MWT) and muscle architecture variables (cross-sectional-area of vastus lateralis (VL-CSA) and cross-sectional-area of rectus femoralis (RF-CSA), thickness of vastus lateralis and pennation angle of vastus lateralis (AP-VL)) were collected. Normality and variance homogeneity were assessed, and Pearson or Spearman correlations were applied as appropriate. Multiple linear regression was performed to evaluate the association between VL-CSA and clinical, functional, and anthropometric variables. Statistical significance was set at p < 0.05. RESULTS: Participants reported high pain intensity (VAS: 7.03 ± 1.94). Mean VL-CSA was 11.73 ± 3.76 cm2. Ultrasound-derived muscle parameters showed significant positive associations with lean mass and anthropometric variables, with a stronger association between VL-CSA and trochanteric circumference than with body mass index (BMI). The regression model explained 46.6% of VL-CSA variance (p < 0.001), with BMI, trochanteric circumference, 5-STST, performance and handgrip strength emerged as independent predictors (p < 0.05), while gait speed was not significant. CONCLUSIONS: Correlations were found between anthropometric variables and muscle architecture. VL-CSA was significantly and independently related to BMI, 4-meter test, 5 sit-stand test, handgrip strength, and trochanter circumference.