19.5 Wednesday, Jan. 4 Does the SLIP Model Apply During Inverted Running in Cockroaches? PARIKH, S.C.*; MARA, K.R.; HSIEH, S.T.; Temple University; Temple University; Temple Unviersity firstname.lastname@example.org
Center of mass (COM) dynamics during upright locomotion is described by the spring loaded inverted pendulum (SLIP) model. According to this model, gravity pulls the COM towards the surface, compressing the virtual leg spring. However, many animals, including cockroaches, have the ability to traverse inverted surfaces. When running upside-down, gravity pulls the COM away from the locomotor surface, extending the virtual leg spring. The goal of this study was to assess the applicability of the SLIP model during inverted running in the orange head cockroach (Eublaberus prosticus). Cockroaches were run on upright and inverted surfaces while being filmed with a high-speed camera at 250 fps. A 45° mirror provided simultaneous dorsal and lateral views. Points were digitized and transformed from 2D to 3D coordinates using custom digitizing software in MATLAB (DLTdataViewer). We expected inverted running COM kinematics would not reflect SLIP model predictions. Contrary to our expectations, when running upside-down, cockroaches exhibit very similar COM kinematics compared to normal, upright runs. Nevertheless, our results do highlight considerable differences in COM position and footfall patterns. While running invertedly, cockroaches shift their COM posteriorly and further from the surface, at the same time positioning their front and hind limbs further medially and laterally, respectively. In addition, the tripod gait typically observed during upright runs was not as stereotyped during inverted locomotion. Inverted locomotion may therefore require a change in leg movement and placement to maintain, at the very least, altered SLIP kinematics for forward progression.