Weakness of the lumbar and hip extensors muscles as well as limited hip flexion mobility have been proposed to contribute to greater lumbar spine loading and greater lumbar flexion during functional tasks. The purpose of the current study was to examine the associations among hip and lumbar spine extension strength, hip flexion mobility and lumbar spine biomechanics during a squat lifting task. Fifty healthy adults participated in the study. Strength of the lumbar extensors and hip extensors was measured using a motor driven dynamometer. Hip range of motion was assessed using a 3D motion capture system. Participants lifted boxes of various weights utilizing a squat lifting technique. Peak lumbar spine and hip flexion were quantified during the final 10% of the descent phase of the squat lifting task. Lumbar spine moments and lumbar paraspinal muscle activity (as measured by electromyography) were quantified during the concentric phase of the squat lifting task. There was a significant positive association between lumbar extensor strength and average lumbar extensor moment during lifting (r=0.50, p<0.01). Similarly, hip extensor strength was positively associated with the average lumbar extension moment (r=0.38, p <0.05). Hip extensor strength was negatively associated with activation of the lumbar paraspinal muscles during lifting (r=-0.38, p<0.05). There was a significant negative association between hip flexion capacity and peak lumbar spine flexion during squat lifting (r=-0.48, p<.001). Similarly, peak lumbar spine flexion was negatively associated with lumbar paraspinal strength (r=-0.38, p<.01). During the squat lift task, peak hip motion was positively associated with hip flexion capacity (r=0.79, p<.001). Stronger individuals are more likely to use their hip extensors and lumbar spine extensors to lift. In contrast, those with lower strength employ subtle biomechanical changes to reduce lumbar spine loading. Diminished hip flexion capacity and lumbar extension strength resulted in greater amounts of lumbar flexion during a squat lifting task. Individuals with greater hip flexion capability utilize less lumbar flexion and greater hip flexion to complete the task. In contrast, those with diminished hip flexion capability and lower lumbar extension strength utilize greater amounts of lumbar flexion.

LLU Discipline

Physical Therapy


Physical Therapy


School of Allied Health Professions

First Advisor

Everett Lohman III

Second Advisor

Lida Gharibvand

Third Advisor

Christopher M. Powers

Degree Name

Doctor of Philosophy (PhD)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Biomechanical Phenomena; Lumbar Vertebrae; Lumbar Vertebrae; Lifting



Page Count

x, 62 p.

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives