Meeting Abstract
The movement of the body during legged locomotion can be modeled using simple mechanical models such as the spring-loaded inverted pendulum (SLIP). SLIP contains a leg that compresses and relaxes during the stance phase tracking the motion of the center of mass (COM) during running. One limitation of SLIP is that it can only model radial forces along the leg, and thus cannot overcome destabilizing gravitational forces. To overcome this limitation, we propose the angular and radial spring-loaded inverted pendulum (ARSLIP). ARSLIP extends SLIP with a torsional spring at the leg-foot joint whose rest position is the vertical orientation of the leg. The resultant tangential forces oppose gravity during the stance phase. The goal of the study is to assess how well SLIP and ARSLIP model the forces and COM kinematics during the single support phase of walking across a range of speeds. During this phase, the horizontal velocity and the vertical height do not change excessively, and the vertical ground reaction force (GRF) is a significant fraction of body weight. We used dimensionless analysis to find the gaitspace, the parameter region that falls within the biologically observed range in height, velocity, and GRF variation. SLIP could model slow walking only for a limited parameter range and only for short steps. ARSLIP can model both slower and faster steps across the parameter space. To further test how well the two models capture the walking gait, both SLIP and ARSLIP were fit to human GRF and COM data during the single support phase. While SLIP can model the M-shaped vertical GRF of human walking, SLIP struggles with the horizontal GRF, overestimating its amplitude. ARSLIP alleviates this issue by bringing the horizontal GRF in line with experimental data.
