Design of an Elastically Suspended Backpack with Tunable Stiffness

Based on the fact that push-off force is the main energy input of human walking, reducing the push-off force when carrying the load is helpful to improve the walking endurance. Previous work has proved that an elastically suspended backpack could change ground reaction forces (GRFs) of legs, and parameters of elastically suspended backpack and walking speeds could affect the push-off force. When the walking speed changes, people hope the elastically suspended backpack to work at their best state by adjusting parameters. In this paper, a simple model is proposed to predict the effect on push-off force. Based on the results of model analysis, an elastically suspended backpack with tunable and appropriate stiffness is designed, which could optimize push-off force by adjusting the stiffness. Two healthy subjects were recruited to attend the experiment using our backpack prototype and the GRFs data was compared. Each subject walked under the multiple conditions (load states: no load, fixed load, elastic load with different stiffness; walking speed: 4.0 km/h, 4.5 km/h, 5.0 km/h, 5.5 km/h). The results show that the elastically suspended backpack could effectively change the stiffness and the effect of push-off force could be improve greatly by changing the stiffness.