UC San Diego

Lumbar spine (LS) problems are the number one cause for medical encounters and lost work time among military personnel. This has been associated with the heavy loads carried during operational duties. Consequently, the effect of load carriage on military performance has been studied extensively. However, LS postural adaptations during load carriage have not been described. Thus, the overall goal of this dissertation is to understand in vivo LS postural response to load carriage in active duty Marines.

This dissertation begins with a feasibility study to demonstrate that LS postural differences between unloaded and loaded tasks are measurable in vivo using an upright magnetic resonance imaging (MRI) scanner. Increased lumbar flexion and reduced lordosis were measured during loaded tasks. In Chapter 3 we examined LS response to load carriage as Marines progressed through the School of Infantry (SOI) Training. Although no effect of training was observed, we found that Marines with disc degeneration carried loads slightly different.

These results suggested that load characteristics determined load carriage posture of the LS, regardless of Marines physical fitness. Therefore, in Chapter 4 we explored the interaction between operationally relevant load magnitudes and distributions on LS posture. Specifically, balancing loads in the anterior-posterior direction yielded lumbar spine postures that are nearly identical to standing. Contrastingly, when load was carried with a posterior bias, superior LS lordosis increased as a function of load magnitude, while inferior LS lordosis was distribution dependent.

These data represent the first in vivo measurements of LS posture under operationally relevant loads. The key findings are: 1) lumbar lordosis is reduced as the spine and hips are flexed forward, 2) improving strength and endurance through training does not appear to change LS behavior during load carriage, and 3) manipulating the load magnitude and distribution does yield significant changes in LS behavior.

Clinically and operationally, these findings are significant because they provide direct, quantitative data that can be used to make informed decisions about load carriage recommendations. Future work may include a longitudinal study to test whether balanced loads prevent injury or enhance operational efficiency in the military.