Immediate Effect of Active Abdominal Contraction on Inter-recti Distance

Controlled laboratory study.

Inter-recti distance (IRD) is the measurement of the linear distance between the medial aspects of the rectus abdominis muscle. Inter-recti distance has been reported to decrease in postpartum women during a curl-up maneuver.

To determine if IRD decreases with active abdominal contraction in men and in nulliparous and parous women.

Fifty-six subjects (male, 11; nulliparous female, 22; parous female, 23) participated. Inter-recti distance was measured with the abdominal muscles at rest and during active contraction (curl-up), at 2 locations (above and below the umbilicus), using ultrasound imaging. A mixed-model, repeated-measures analysis of covariance was used for each of the 2 locations, to determine whether IRD differed between contraction states among the 3 groups, with age and umbilicus circumference as covariates. When significant differences were found, planned t test comparisons were made.

The parous group's IRD significantly decreased from rest to contraction at both locations, whereas the nulliparous and male groups' IRD did not significantly change from rest to contraction. The nulliparous group's IRD was significantly narrower than the other groups at rest at both locations, and narrower than the parous group during active contraction.

Parous women had a narrower IRD in the curl-up condition than at rest, as hypothesized. However, an unexpected finding of a lack of significant within-group change in IRD in nulliparous women and men occurred. Findings suggest that the IRD in men may only differ from that of nulliparous women.