Influence of Menopause on Mechanical Properties of Pelvic Floor and Lumbar Paravertebral Muscles: A Cross-Sectional...

Menopause is associated with physiological changes that could alter the muscle mechanical properties (MMPs) of the pelvic floor (PF). This study aimed to investigate the influence of menopause on the mechanical properties of lumbopelvic muscles, with PF muscles as the primary outcome and lumbar paravertebral muscles as a secondary outcome, comparing postmenopausal and premenopausal women while adjusting for age and body mass index (BMI).

A cross-sectional observational study was conducted involving 20 postmenopausal and 20 premenopausal women aged 45-65 years. MMPs, that is, frequency (tone), stiffness, decrement (inverse of elasticity), and viscoelastic properties (relaxation time of stress, and creep, that represents fluidity), were bilaterally assessed at the PF and lumbar paravertebral level using a device measuring MMPs (MyotonPRO). Sociodemographic and clinical variables (PFDI-20 and PFIQ-7 questionnaires) were also recorded. Between groups comparisons were performed, according to data distribution, and analysis of covariance, adjusted by age and BMI as covariates, were applied to all MMPs of both regions.

Postmenopausal women showed significantly higher values for frequency (1.25 Hz, 95% confidence interval (CI) [0.26, 2.23]) and stiffness (40.20 N/m, 95% CI [5.74, 74.66]) on the left side of PF. However, frequency differences were no longer significant after adjustment for age and BMI and left-side stiffness remained associated with age rather than BMI. In contrast, premenopausal women exhibited significantly greater viscoelastic properties at both sides, independently of age and BMI. No significant differences were observed in the MMPs of the lumbar paravertebral muscles (p > 0.05).

MMPs of the PF differed between postmenopausal and premenopausal women. After adjustment for age and BMI, group differences were attenuated; viscoelastic parameters remained different between groups, while increased PF stiffness appeared primarily age-related. No influence by menopausal status was observed at the lumbar level.