Acronym Required previously reported on research about Nepalese porters who carry increased loads on their heads without having to increase their metabolic cost to the extent that thermodynamics would predict. African women utilize the same energy gains to carry heavy loads - also on their heads. Human gait works like an imperfect inverted pendulum; muscles propel about 35% of the energy fluctuations forward and back, up and down, and up to 65% of the energy is cancelled. The economized gait of the Nepalese porters and the African women is acquired with practice apparently, since novice walkers who try to carry loads on their heads cannot reproduce the same energy gains, they only (obviously) get sore necks.
Recently a much reported Science publication by University of Pennsylvania researchers tested a theory that the net energy gains of load bearing locomotion could be harnessed. To take advantage of the energy fluctuations in the up and down motion of walking they designed and built a knapsack incorporating springs and a mechanism that drives a generator onto an external frame. The load of the knapsack is allowed to move freely on the frame and the energy propelled by the load movement during walking powers a generator that can be used in lieu of batteries.
"Conceptually, it resembles the self-winding mechanism of an automatic wristwatch, where power is generated from an oscillating payload, excited inertially through the wearer's motion. Neither force nor displacement is imposed; both arise from the device's dynamics."
It will be interesting to see whether such packs can be optimized for use. We were initially skeptical because although the load only moved up and down 4.5 centimeters in their study, it seemed that the extra movement could create imbalance which could limit usefulness. The researchers report that the pack is reportedly comfortable however. As shown by the porters and African women, the extra energy involved with carrying the knapsack-generator device costs less metabolically then calculations show would be required both for powering the generator and for carrying the load. The research with the African women pointed out the different metabolic costs between load carrying on one's head, as opposed to a knapsack. Though a similiar mechanism is obviously in play, it's clearly not solely due to a difference in load placement. Previous attempts to harness energy from walking focused on generating energy from shoes or by attaching devices to moving limbs. It will be exciting to fully elucidate how this works and as well the experiments offer potential for alternative energy production in remote (or disaster prone) areas.
