Effects of a Lumbar Support Cushion in a Backpack on Postural Alignment and Skeletal Muscle Mechanical Properties: A Repeated-Measures Trial in Healthy Adults

Background/Objectives: Backpacks are widely used for carrying loads; however, posteriorly positioned loads can shift the body’s center of mass, promote forward trunk and head compensation, and increase neck and shoulder muscle loading. This study examined the effects of a detachable lumbar support cushion at loads equivalent to 10%, 15%, and 20% of the body weight. Methods: Twenty-eight healthy adult men completed repeated-measures trials of backpacks without or with lumbar support cushions. The craniovertebral angle (CVA), forward trunk lean (FTL), pelvic tilt angle (PTA), upper trapezius, sternocleidomastoid (SCM) tone, and stiffness were assessed. The trial registration was completed by the Clinical Research Information Service of the Republic of Korea (KCT0012211). Results: Most variables changed significantly as the load increased, with the largest changes occurring up to 15% and limited additional changes between 15% and 20%. The cushion did not significantly affect CVA or FTL but increased PTA and reduced SCM tone. Conclusions: A detachable lumbar support cushion may modify the PTA and was associated with lower SCM tone during backpack carriage.