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

To compare muscle thickness of rectus abdominis, internal oblique, external oblique, and transversus abdominis between rest and PFM isolated contraction.

Cross-sectional reliability study.

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.

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.

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.