Background and purpose: Low abdominal hollowing in four-point kneeling is used clinically to test and rehabilitate transversus abdominis (TrA) but many people find this exercise difficult to perform. Contracting pelvic floor muscles (PF) during low abdominal hollowing may facilitate contraction of TrA. Thickness increase in the abdominal muscles during low abdominal hollowing has been measured with real-time ultrasound scanning and may indicate muscle contraction. The present study investigated the effect of instructing PF contraction on TrA thickness increase during low abdominal hollowing.
Method: Twelve females and eight males with no reported pelvic floor dysfunction or low back pain in the last two years were taught low abdominal hollowing in four-point kneeling. Subjects performed low abdominal hollowing with and without instruction to contract PF in random order. Transversus abdominis, obliquus internus (OI) and obliquus externus (OE) thickness were measured with ultrasound scanning at rest and during both tests.
Results: Mean increase in TrA thickness during low abdominal hollowing was 49.71% (SD 26.76%), during low abdominal hollowing with PF it was 65.81% (SD 23.53%). Paired Student's t-tests indicated a significant difference between tests (p = 0.015). There were no significant differences between tests for OE or OI thickness increase.
Conclusions: Instructing healthy subjects to co-contract PF results in greater increase in TrA thickness during low abdominal hollowing in four-point kneeling. This may indicate greater contraction of TrA and thus be useful for clinicians training TrA. Further research could investigate the validity of change of thickness as a measure of abdominal muscle contraction, investigate the effect of instructing PF co-contraction on TrA in patients with low back pain and measure PF and TrA activity simultaneously.