Immediate Effect of Four Exercises on Linea Alba Thickness, Distortion and Inter-Recti Distance in Parous Women.

These are measurements taken during single repetitions in one session. The study cannot tell you what happens over weeks of training, or whether any of it changes pain, function, confidence or appearance. Ultrasound is an accepted way to measure the gap between the muscles, but the authors say it is not validated for linea alba thickness or for the deformation measure, so those two results rest on shakier ground than the gap result. The deformation results came from statistical models that did not meet the assumptions required; the authors re-ran them with a different test and got the same answer, but still say those findings need confirming. Two different ultrasound machines were used and the authors did not formally cross-check them against each other, which they say could shift the absolute values slightly. The women were recruited by flyer at one institute, and the sample included multiparous women with no fixed time since childbirth, so it may not match the women you see in the early postpartum months.

The authors say they have nothing to report on funding. One author, B.G., declares a potential conflict of interest as the developer of the de Gasquet method, which was one of the four exercises tested. On every outcome measured, that exercise behaved the same as the drawing-in and pelvic floor exercises.

Do not read this as showing the crunch is harmful or that one exercise is the right one to prescribe. The greater linea alba deformation during the crunch was an ultrasound measurement taken during single repetitions in a single session, no clinical outcome was measured, and the study did not follow anyone over time. The authors themselves state these findings should not be taken as evidence of clinical effectiveness.