Coordination variability during load carriage walking: can it contribute to low back pain?

Load carriage walking is frequently associated with low back pain. Mechanical stress is a potential cause of such pain, and a lack of coordination variability may produce mechanical stress. We tested the hypothesis that coordination variability would decrease during load carriage walking. We examined the trunk-thigh coordination variability in the sagittal and frontal planes and the thorax-pelvis coordination variability in the transverse plane. Ten healthy participants were recruited to perform unloaded and load carriage walking. Coordination variability was quantified as the standard deviation of continuous relative phase between two segments across a number of walking trials. During load carriage walking, the coordination variability significantly increased rather than decreased in the sagittal and transverse planes, and it did not change significantly in the frontal plane compared to those during unloaded walking. The findings rejected the hypothesis and suggested that reduced coordination variability may not predict the development of low back pain associate with load carriage walking in healthy people.