A Model for Estimating the Leg Mechanical Work Required to Walk With an Elastically Suspended Backpack

The mechanical work performed by the individual legs affects the metabolic cost of locomotion. The effects of an elastically suspended backpack (ESB) on the mechanical work performed by the individual legs have not yet been quantified. This article explores the impact of variables, such as the stiffness and damper of an ESB, walking speed, and load mass, on the leg mechanical work (LMW). A model integrating an improved bipedal walking submodel and a spring-mass-damper submodel is proposed to estimate the mechanical work performed by the individual legs (LMW model). Experimental data were collected to estimate the accuracy of the proposed model. Seven subjects walked with a loaded ESB prototype at speeds ranging from 3.6 to 6.0 km/h with the suspension engaged and with the suspension locked out. The measured mechanical work performed by the individual legs was compared to the LMW model estimates. The proposed model estimates corresponded well with the empirical results (average R2 = 0.909; estimated average error 3.6%). The LMW model was then used to simulate the effects of variables. The ESB produces positive or negative effects under different variables. With increasing ESB stiffness, the ESB first produces positive effects, then negative effects, and finally approaches the rigid backpack effect. The ESB damper also affects the magnitude of the effect. The smaller the damping, the larger the effect. These results could assist engineers trying to design ESB to minimize the mechanical work performed by the legs which may also minimize the metabolic energy cost.