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Effect of Load Magnitude and Distribution on Lumbar Spine Posture in Active-duty Marines

Rodríguez-Soto, Ana E. PhD; Berry, David B. MSc; Palombo, Laura MSc; Valaik, Emily BS; Kelly, Karen R. PT, PhD; Ward, Samuel R. PT, PhD

doi: 10.1097/BRS.0000000000001742
Occupational Health/Ergonomics

Study Design. Repeated measures.

Objective. The purpose of this study was to quantify the effect of operationally relevant loads and distributions on lumbar spine (LS) in a group of active-duty Marines.

Summary of Background Data. Low-back pain has been associated with heavy load carriage among military personnel. Although there are data describing the LS posture in response to load, the effect of varying load characteristics on LS posture remains unknown.

Methods. Magnetic resonance images of Marines (n = 12) were acquired when standing unloaded and when carrying 22, 33, and 45 kg of load distributed both 50% to 50% and 20% to 80% anteriorly and posteriorly. Images were used to measure LS and pelvic postures. Two-way repeated-measures ANOVA and posthoc tests were used to compare LS posture across load magnitudes and distributions (α = 0.05). This project was founded by the US Army Medical Research Acquisition Activity, Award No. W81XWH-13–2–0043, under Work Unit No. 1310.

Results. No changes in LS posture were induced when load was evenly distributed. When load was carried in the 20% to 80% distribution lumbosacral flexion increased as a result of sacral anterior rotation and overall reduced lumbar lordosis. This pattern was greater as load was increased between 22 and 33 kg, but did not increase further between 33 and 45 kg. We observed that the inferior LS became uniformly less lordotic, independently of load magnitude. However, the superior LS became progressively more lordotic with increasing load magnitude

Conclusion. Postural adaptations were found only when load was carried with a posterior bias, suggesting that load-carriage limits based on postural changes are relevant when loads are nonuniformly distributed. Although the tendency would be to interpret that loads should be carried symmetrically to protect the spine, the relationship between postural changes and injury are not clear. Finally, the operational efficiency of carrying load in this distribution needs to be tested.

Level of Evidence: 3

*Departments of Bioengineering, University of California, San Diego, CA

Departments of Radiology, University of California, San Diego, CA

Departments of Orthopedic Surgery, University of California, San Diego, CA

§Warfighter Performance Department, Naval Health Research Center, San Diego, CA

Department of Exercise and Nutritional Sciences, San Diego State University, San Diego, CA.

Address correspondence and reprint requests to Samuel R. Ward, PT, PhD, Departments of Radiology, Orthopedic Surgery, and Bioengineering, University of California, San Diego, 9500 Gilman Drive (0863), La Jolla, CA 92093; E-mail: srward@ucsd.edu

Received 30 September, 2015

Revised 10 April, 2016

Accepted 25 May, 2016

The manuscript submitted does not contain information about medical device(s)/drug(s).

The US Army Medical Research Acquisition Activity, Award No. W81XWH-13–2–0043, under Work Unit No. 1310 funds were received in support of this work.

No relevant financial activities outside the submitted work.

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