Normative ability of young females to control the lumbopelvic curvature during active knee extension in sitting

[Purpose] Active unilateral knee extension in sitting (AUKEiSit) is a clinical test for lumbopelvic control during limb movements. We aimed to identify the normal upper limit for the angle of lumbopelvic sagittal alignment (θ) during AUKEiSit in young females. [Participants and Methods] The primary inclusion criteria of the participant included asymptomatic females 18–44 years of age. Lumbopelvic curvature from T12 to S2 was traced on paper using a flexible ruler during right AUKEiSit. The θ value was calculated using 2 methods: 1) 2-point-method, calculating the angle between 2 tangential lines at T12 and S2 on a trace line using Image J software; and 2) max-method, calculating θ by measuring the distance between T12 and S2 and the maximum depth of the curvature. A negative value of θ indicated lumbar lordosis. The mean and 95% confidence intervals (CIs) were computed with bootstrapping. [Results] The data of 121 participants (mean age: 20.6 years) were analyzed. The mean and 95% confidence intervals of θ were −12.06° (−14.03° to −9.40°) with the 2-point-method and −5.40° (−7.62° to −2.73°) with the max-method. [Conclusion] In asymptomatic young females, the 95% confidence intervals of θ during AUKEiSit are negative regardless of the 2 different methods.