The influence of hip flexion mobility and lumbar spine extensor strength on lumbar spine flexion during a squat lift

Cross-sectional; Controlled laboratory study.To examine the associations among available hip flexion motion, lumbar extensor strength and peak lumbar flexion during a squat lift task.Lumbar spine flexion during lifting can result in increased strain on spinal structures. Although decreased available hip flexion motion and reduced strength of the lumbar extensor muscles has been proposed to contribute to greater lumbar flexion during lifting, direct relationships have not been explored.Fifty healthy young adults participated (23 males and 27 females). Strength of the lumbar extensors was measured using a motor-driven dynamometer. Available hip flexion was assessed using 3D motion capture. Peak lumbar spine flexion and hip flexion were quantified during the descent phase of the squat lifting task.There was a significant negative association between available hip flexion and peak lumbar spine flexion during squat lifting in females (r = -0.407, p = 0.035) but not males (r = -0.341, p = 0.120). Similarly, peak lumbar spine flexion was negatively associated with lumbar extensor strength in females (r = -0.398, p = 0.040) but not males (r = -0.310, p = 0.161). During the squat lift, peak hip motion was positively associated with available hip flexion for both males and females combined (r = 0.774, p 0.001).Females with less available hip flexion and lower lumbar extensor strength exhibit greater lumbar flexion when performing a lifting task. Clinicians should be aware of the potential contributions of such impairments when instructing patients into various lifting strategies.