Temporal trends in trunk flexor endurance and intra-abdominal pressure in postpartum women.

: To describe change in trunk flexor endurance and intra-abdominal pressure (IAP) associated with trunk flexor assessment and explore factors associated with change in trunk flexor endurance during the first postpartum year.: Ancillary analysis of an ongoing prospective cohort study.: Participants (N = 282) were primiparous women delivered vaginally. They completed trunk flexor endurance testing while assessing IAP, body habitus measures (body mass index, waist circumference, and body composition), and questionnaires 5-10 weeks and 11-15 months postpartum. We investigated change in trunk flexor endurance by quartile of improvement and factors associated with improvement (Q4 vs. Q1-Q3) using multivariable models, adjusted for baseline endurance.: Mean age was 28 ± 5 years. The median (IQR) trunk flexor hold time increased from early to late postpartum (129/IQR = 68, 217 vs 148/IQR = 80, 265 seconds, = .01) and mean (SD) IAP decreased (55/SD = 13 vs 48/SD = 14 cmH0, < .0001). The most improved group (Q4) increased endurance time by 176 seconds (95% CI = 103, 254), were less likely to be Hispanic, more likely to be older, more educated, and have lower measures of body habitus than women in Q1-Q3. : Trunk flexor endurance increased and IAP decreased over one year postpartum. Lower body habitus and higher age early postpartum predicted greatest improvement in trunk flexor endurance at 1 year.