A Bipedal Walking Model Considering Trunk Pitch Angle for Estimating the Influence of Suspension Load on Human Biomechanics

Objective: Suspended loads have been shown to improve loaded-walking economy. Establishing a biped walking model with dynamic trunk pitch angles can provide more comprehensive estimates of the human biomechanical response under suspended loads. Methods: We developed the trunk-load- hip dynamics, modified the spring-loaded-inverted-pendulum (SLIP) model, and optimized the loaded-walking pattern for minimal energetic cost. 9 subjects participated in experiments using a powered backpack to validate the model's performance, conducting two trials: Load-Suspended (LS) and Load-Locked (LL). Results: The averaged correlation coefficient of simulated and experimental hip trajectory, vertical and horizontal GRFs, and individual leg mechanical (ILM) powers are 0.96, 0.97, 0.93, and 0.81, respectively. The RMS error between simulated and experimental peaks of vertical GRFs, braking peaks of horizontal GRFs, and energetic costs was under 10%. Simulation also provides observation on the effect of suspended load on dynamic trunk pitch angles and torques, and leg stiffness. Both the simulation and experiment demonstrated the advantages of LS in reducing GRFs and energetic cost. Additionally, the simulation shows the peaks of trunk flexion and extension torque are reduced by 34.77% (p < 0.05) and 37.88% (p < 0.05) in LS. Conclusion: The model effectively estimates hip trajectory, vertical and horizontal GRFs, ILM powers, and energetic cost, and provides observations on trunk behavior under different load conditions. The model also supports the advantages of suspension load. Significance: Appropriate models could comprehensively reveal the mechanism between the mechanical systems and human biomechanics responses, guide the design of carrying load devices, and provide rapid evaluation of its effects.