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.

Suspending loads decreases load stability but may slightly improve body stability

“…In another experimental study, participants carrying a load with a compliant bamboo pole reported that "balancing the pole was difficult and uncomfortable" (Castillo et al, 2014). The awkward feeling noted by the subjects in these studies could have been caused by asymmetric loading, insufficient habituation, or the challenge of balancing a long pole on their shoulder (Potwar et al, 2014), but we expect that part of this awkward feeling is a result of the reduced stability of a compliant load.…”

“…They also have some direct control over the load motion by manipulating a control arm attached to the camera sled gimbal, which could help to actively damp perturbations or to give the user a feeling of control through tactile feedback. Users of bamboo carrying poles also appear to hold the suspended load or pole to help stabilize the load (Balogun, 1986;Castillo et al, 2014;Datta and Ramanathan, 1971;Kenntner, 1969;Kram, 1991;Potwar et al, 2014).…”

“…The first documented use of a highly-compliant load suspension are humans carrying heavy loads with compliant bamboo carrying poles, which were initially adopted in Southeast Asia (Castillo et al, 2014;Kram, 1991;Potwar et al, 2014) (Figure 1a). More recently, various highly-compliant suspension systems have been developed to assist humans carrying heavy camera systems using the Steadicam® stabilizing arm Jurgens, 1978) (Figure 1b), backpack loads (Foissac et al, 2009;Rome et al, 2006Rome et al, , 2005 (Figure 1c), and hand-held loads .…”

Effects of stride frequency and foot position at landing on braking force, hip torque, impact peak force and the metabolic cost of running in humans

“…where f is the ventilation flow rate in the mask at steady-state, O 2,i is the initial percentage O 2 measured prior to the trial, O 2,f is the final percentage O 2 at the end of the trial, O 2,ss is the mean percentage O 2 measured at steadystate, T ss is the time when O 2,ss was measured, T i is the time when O 2,i was measured and T f is the time when O 2,f was measured (Perl et al, 2012;Castillo et al, 2014). Oxygen consumption data were sampled using LabChart over a 5-7 min period until participants reached at least 2 min at a flat, steady-state VȮ 2 plateau in which the slope was not significantly different from 0 (Whipp and Wasserman, 1972).…”

Minimally Actuated Walking: Identifying Core Challenges to Economical Legged Locomotion Reveals Novel Solutions

“…It is hypothesized that an individual will choose motor patterns based on the principle of energy minimization, in which, the optimal work-based solutions discovered by the optimal control problem reflect the coupled oscillator interaction chosen. Although current literature suggests that humans sometimes adapt gait patterns to accommodate elastic load oscillations to reduce metabolic exertion (Rome et al, 2005(Rome et al, , 2006Castillo et al, 2014;Ackerman and Seipel, 2014), more evidence is needed to show that humans can employ energy minimization strategies consistent with the interactions proposed by the forced coupled oscillator mechanism described. Still, realistic system constraints and considerations can be implemented for the applied problem.…”