title: Effects of pole compliance and step frequency on the biomechanics and economy of pole carrying during human walking.
abstract: This study investigates whether a flexible pole can be used as an energy-saving method for humans carrying loads. We model the carrier and pole system as a driven damped harmonic oscillator and predict that the energy expended by the carrier is affected by the compliance of the pole and the ratio between the pole's natural frequency and the carrier's step frequency. We tested the model by measuring oxygen consumption in 16 previously untrained male participants walking on a treadmill at four step frequencies using two loaded poles: one made of bamboo and one of steel. We found that when the bamboo pole was carried at a step frequency 20% greater than its natural frequency, the motions of the centers of mass of the load and carrier were approximately equal in amplitude and opposite in phase, which we predicted would save energy for the carrier. Carrying the steel pole, however, resulted in the carrier and loads oscillating in phase and with roughly equal amplitude. Although participants were less economical using poles than predicted costs using conventional fixed-load techniques (such as backpacks), the bamboo pole was on average 5.0% less costly than the steel pole. When allowed to select their cadence, participants also preferred to carry the bamboo pole at step frequencies of ∼2.0 Hz. This frequency, which is significantly higher than the preferred unloaded step frequency, is most economical. These experiments suggest that pole carriers can intuitively adjust their gaits, or choose poles with appropriate compliance, to increase energetic savings.
authors.affiliation: Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts; ercastil@fas.harvard.edu.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Castillo
authors.affiliation: Harvard University Medical School, Boston, Massachusetts; and.
authors.forename: Graham M
authors.initials: GM
authors.lastname: Lieberman
authors.affiliation: Department of Physics and Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts.
authors.forename: Logan S
authors.initials: LS
authors.lastname: McCarty
authors.affiliation: Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts;
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Lieberman
mesh_terms: D000293:Adolescent; D000465:Algorithms; D000886:Anthropometry; D001696:Biomechanical Phenomena; D004734:Energy Metabolism / Q000502:physiology*; D006801:Humans; D008297:Male; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology; D016138:Walking / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult
keywords: energetics; gait; harmonic motion; load carrying; locomotion; mass-spring model; natural frequency