Altering Compliance of a Load Carriage Device in the Medial-Lateral Direction Reduces Peak Forces While Walking

Abstract

Altering mechanical compliance in load carriage structures has shown to reduce metabolic cost and accelerative forces of carrying weight. Currently, modifications to load carriage structures have been primarily targeted at vertical motion of the carried mass. No study to date has investigated altering load carriage compliance in the medial-lateral direction. We developed a backpack specifically for allowing a carried mass to oscillate in the horizontal direction, giving us the unique opportunity to understand the effects of lateral mass motion on human gait. Previous modelling work has shown that walking economy can be improved through the interaction of a bipedal model with a laterally oscillating walking surface. To test whether a laterally oscillating mass can experimentally improve walking economy, we systematically varied step width above and below the preferred level and compared the effects of carrying an oscillating and fixed mass. Walking with an oscillating mass was found to reduce the accelerative forces of load carriage in both horizontal and vertical directions. However, load eccentricity caused the vertical force component to create a significant bending moment in the frontal plane. Walking with an oscillating mass led to an increase in the metabolic energy expenditure during walking and an increase in positive hip work during stance. The device’s ability to reduce forces experienced by the user, due to load carriage, holds promise. However, the requirement of additional metabolic energy to walk with the device requires future study to improve.

Generating electricity while walking with a medial–lateral oscillating load carriage device

“…As with the previous experiment [18] using the load-carriage device (with no energy harvesting module), we observed a reduction in the M–L interaction force when the mass was oscillating, compared to fixed. However, we did not observe in this current study a reduction in vertical interaction force as we had with the previous study.…”

“…This new dimension in device control was used in this study to determine optimal device behaviour, resulting in favourable device–user interaction. Mass oscillation amplitude was identified in our passive M–L load carriage evaluation study [18] to be a possible way to reduce the frontal plane interaction moment, where the frontal plane interaction moment was thought to be a potential reason for the increase in metabolic power when walking with the passive version of the device. By changing the amount of damping present, we were able to effectively control mass oscillation amplitude and decrease the frontal plane interaction moment, demonstrating the device’s capabilities to exert varying device–user interaction dynamics.…”

“…The energy harvesting backpack consists of an M–L load carriage device, described in [18], and an energy harvesting module (figure 1). The medial-lateral load carriage device uses cylindrical weights, simulating carried weight (mass = 9 kg), suspended on an inverted pendulum (length = 30 cm).…”

Allowing the Load to Swing Reduces the Mechanical Energy of the Stance Leg and Improves the Lateral Stability of Human Walking

“…The reduction in the lateral excursion of xCoM induced by the lateral load oscillation out of phase to the human CoM indicates the increase of MoS, and further implies the improvement in lateral stability. The backpack with load compliance in the lateral direction found similar results, including the load oscillation out of phase to the subjects, the reduction in horizontal impulses, and the reduction in the preferred step width [30]. Moreover, the effect of the swinging load in the mediolateral direction could also be viewed as an equivalent external lateral stabilizer [28] pulling bilaterally from the waist with springs.…”

“…Besides, external lateral forces that are out of phase with the lateral displacement of the human center of mass (CoM) have been shown to improve the lateral stability and the energy efficiency of walking [28], [29]. Moreover, the backpack with load compliance in the lateral direction via an inverted pendulum mechanism allows the load to oscillate out of phase with the carrier laterally, and reduce the peak GRFs while walking [30]. Overall, the horizontal relative load movement should result in different interaction forces between the load and the carrier compared to the typical rigidly-attached backpack, further affecting the biomechanics and energetics of loaded walking.…”