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

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.