Inter-rectus distance in postpartum women can be reduced by isometric contraction of the abdominal muscles: a preliminary case–control study

ObjectivesTo determine the effect of isometric contraction of the abdominal muscles on inter-rectus distance in postpartum women.DesignPreliminary case–control study.SettingResearch laboratory.ParticipantsTen postpartum women {mean age 30 [standard deviation (SD) 4] years; mean weight 58 (SD 7) kg; mean height 159 (SD 4) cm} and 10 nulliparous (control) women [mean age 28 (SD 2) years; mean weight 56 (SD 6) kg; mean height 160 (SD 6) cm].InterventionsUltrasound images from the anterior abdominal wall were recorded at rest (supine position) and during an abdominal isometric contraction, with the subject actively performing an abdominal crunch (crook lying position). Two-way analysis of variance was used to compare the inter-rectus distance between groups (postpartum vs control) and between levels of abdominal muscle activation (rest vs isometric contraction).Main outcome measuresInter-rectus distance 2 cm above the level of the umbilicus.ResultsThe inter-rectus distance was significantly greater in the postpartum group compared with the control group [14.7 (SD 3.1) mm vs 9.6 (SD 2.8) mm; mean difference 5.1 mm; 95% confidence interval (CI) 3.4 to 6.8]. The inter-rectus distance was significantly lower during isometric contraction compared with rest [10.7 (SD 3.1) mm vs 13.4 (SD 3.1) mm; mean difference 2.8 mm; 95% CI 1.2 to 4.5]. No interaction was found between group and muscle contraction.ConclusionsThe inter-rectus distance was significantly higher in postpartum women compared with controls, and significantly lower during isometric contraction of the abdominal muscles (abdominal crunch) compared with rest.