Biomechanical and Musculoskeletal Differences Between Postpartum Runners and Nulliparous Controls

Abstract

Background: Women are running as soon as 8 weeks postpartum and there is currently little understanding of the effects of pregnancy and childbirth on the postpartum runner (PPR). Pregnancy-related musculoskeletal and physiological changes could impact running gait postpartum. Objective: The purpose of the current study was to investigate differences in overground running kinetics, strength and flexibility in PPRs, and age-matched nulliparous controls. Methods: Vertical and anteroposterior ground reaction force (APGRF) data were collected during overground running and normalized to body weight (NBW). Hip and knee strength, and hamstring flexibility measures were collected using a handheld dynamometer and inclinometer, respectively. Data were averaged for both legs. Independent-samples t tests and effect size (ES) estimations were conducted using α = .05. Findings: Nine PPRs (33.10 ± 5.60 years; ≤2 years postpartum) and 9 age-matched nulliparous women (31.67 ± 4.55 years) participated. PPRs had 24.3% greater braking loading rate for APGRF than controls (mean difference [MD] 3.41 NBW/s, 95% confidence interval [CI] 0.08, 6.74; P = .046; ES 1.08). PPRs had 14% less hamstring flexibility (MD 10.98°, 95% CI 0.97, 20.99; P = .034; ES 1.14), 25.9% less hip abduction strength (MD 0.04 NBW, 95% CI 0.00, 0.08; P = .045; ES 1.07) and 51.6% less hip adduction strength (MD 0.06 NBW, 95% CI 0.02, 0.10; P = .003; ES 1.68). Interpretation: These preliminary findings suggest that PPRs demonstrate altered running braking strategies and decreased hamstring flexibility and hip strength compared with nulliparous controls. As running guidelines for PPRs have been derived mostly from expert opinion, this exploratory cohort study suggests that PPRs should be evaluated for musculoskeletal impairments before initiating or returning to running. (See the Video, Supplemental Digital Content A, available at: http://links.lww.com/JWHPT/A67, which discusses the significance, innovation, and clinical applicability of this study.)