Biomechanical comparisons considering risk to the lumbar spine: walking with no load, a backpack, and a person on the back
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Participants were twelve 70+ kg male strength-trained athletes and one passenger child with a mass of 29 kg. The male participants walked three times over a force plate embedded in an eight metre walkway for each of three conditions: carrying no load, a 29 kg backpack, or a 29 kg passenger. Variables were compared using a repeated measures ANOVA test with a Bonferroni correction. Both load conditions produced compensatory trunk flexion; trunk flexion increased from no load to piggybacking to backpacking. Trunk range of motion was similar for no load and piggybacking, but increased to backpacking. The backpack load caused greater resultant and total magnitude of torque than the passenger load. The trunk extensors dominated with no load and piggybacking and the trunk flexors dominated with backpacking. Many of the significant differences between conditions suggest that piggybacking is biomechanically more similar to natural gait than is backpacking.