The Role of Trunk Mechanics in Uphill and Downhill Walking: A Simulation and Experimental Study

The Spring-Loaded Inverted Pendulum (SLIP) model has been widely used to study bipedal locomotion, effectively capturing the fundamental dynamics of walking and running on level surfaces. However, its constant energy level presents a challenge when modeling locomotion on slopes, where energy input is required for ascending and dissipation is necessary for descending. Introducing a trunk into the SLIP model adds degrees of freedom, enabling energy adjustments through trunk dynamics. However, this also raises challenges in controlling trunk movement and hip torque. The virtual pivot point (VPP) concept and the force-modulated compliance (FMC) model have been proposed as effective strategies for trunk control on level ground, but their effectiveness in slope walking remains unexplored. This study investigates whether incorporating a trunk into the SLIP model and VPP and FMC-based control strategies can facilitate locomotion on inclined terrains. By combining simulation and experimental studies, we assess how trunk dynamics contribute to energy modulation during uphill and downhill walking. Our findings improve our understanding of bipedal locomotion on slopes, providing insights to develop more accurate biomechanical models and improve assistive device design.