Changes in abdominal muscles’ thickness from rest to pelvic floor isolated contraction in healthy women

OBJECTIVES: To compare muscle thickness of rectus abdominis, internal oblique, external oblique, and transversus abdominis between rest and PFM isolated contraction. DESIGN: Cross-sectional reliability study. METHODS: Muscle thickness from rectus abdominis, internal oblique, external oblique and transversus abdominis was obtained from 27 physically active women (age: 26.41 ± 0.77 years) with ultrasound imaging at rest and during three maximum PFM contractions. Two independent analyzers, blinded to the conditions, analyzed 3 images from each muscle and condition using Image-J 1.42q software. Muscle thickness was measured three times on each image. Differences between conditions (rest and PFM contraction) were analyzed with a Student t-test. To verify the outcome measures' inter-analyzer reliability, the intraclass correlation coefficient (ICC), standard error of the measurement (SEM), and minimum detectable change (MDC) were calculated. RESULTS: TrA showed a significant increase in muscle thickness from rest compared to PFM isolated contraction (p < 0.001; t:-4.137). However, muscle thickness was similar for the two conditions in rectus abdominis (p = 0.093; t:1.746), internal oblique (p = 0.410; t:0.838), and external oblique (p = 0.847; t:0.196). Excellent reliability was found for muscle thickness at rest (r = 0.828-1.000; p < 0.001) and during PFM contraction (r = 0.997-1.000; p = 0.001) for rectus abdominis, internal oblique, external oblique and transversus abdominis muscles. SEM and MDC values from all outcomes were low. CONCLUSION: PFM isolated contraction generates a significant contraction of the transversus abdominis muscle, which helps controlling intra-abdominal pressure. The excellent inter-analyzer reliability evidence that abdominal muscles' muscle thickness is reliable when obtained by different analyzers.