The Influence of Relative Hamstring Flexibility and Lumbar Extensor Strength on Lumbar and Pelvic Kinematics During a Stoop Lift

The objective of this study was to examine the influence of relative hamstring flexibility and lumbar extensor strength on lumbar flexion during a stoop lift. Lumbar flexion during stoop lifting has been associated with increased bending stress and load on the lumbar spine. The potential impairments that contribute to a flexed lumbar lifting posture during stoop lifting are unclear. Forty-nine healthy individuals (27 females and 22 males) between the ages of 18 and 40 participated. Strength of the lumbar extensors was measured with a motor-driven dynamometer, and relative hamstring flexibility was estimated with the passive knee extension test. Peak lumbar flexion and pelvis anterior rotation were quantified with 3D motion capture during a stoop lift. There was a positive correlation between relative hamstring flexibility and peak pelvis anterior rotation angle during the stoop lift (r = .544, P < .001). Meanwhile, there was a negative correlation between middle lumbar spine peak flexion and relative hamstring flexibility (r = -.538, P < .001) and a negative correlation between lumbar extensor strength and lower lumbar peak flexion (r = -.288, P = .045). Individuals with decreased strength and limited relative hamstring flexibility tended to exhibit increased lumbar flexion during stoop lifting.