Intra- and inter-rater reliability of ultrasound measurements of the levator ani muscle thickness in and M-mode in asymptomatic individuals: a cross-sectional study.

Background: The levator ani muscle (LAM) plays a crucial role in maintaining pelvic floor function, providing support to pelvic organs and assisting in physiological processes such as micturition and defecation. Ultrasound imaging, particularly M-mode ultrasound, has been increasingly employed in the evaluation of pelvic floor muscle activity. Objectives: The goal of the present study was to assess the intra- and inter-rater reliability of M-mode ultrasound measurements of LAM thickness, muscle activation speed, and contraction time during a 5-s sustained pelvic floor contraction in asymptomatic women. Methods: Thirty-four healthy nulliparous women aged 18 to 25 were recruited for this cross-sectional study. Transabdominal M-mode ultrasound was used to measure the intra- and inter-rater reliability of LAM thickness during maximum pelvic floor contraction. Each participant performed three pelvic floor contractions, with measurements repeated twice. Results: Intra-rater reliability ranged from poor to good reliability for LAM thickness (ICC = 0.621-0.899), with similar results for pelvic rise time and contraction velocity. Inter-rater reliability was excellent for LAM thickness (ICC = 0.910) but only fair for pelvic rise time and contraction velocity (ICC = 0.673-0.647). Conclusions: M-mode ultrasound imaging demonstrates excellent inter-rater reliability for LAM thickness measurement and fair intra-rater reliability for other functional variables. This technique appears to be a promising method for evaluating pelvic floor muscle activity.