Meeting Abstract

P3.199  Sunday, Jan. 6  Swing Leg Control: Disturbance rejection versus injury avoidance BLUM, Y*; BIRN-JEFFERY, AV; VEJDANI, HR; HURST, JW; DALEY, MA; Royal Veterinary College, London, UK; Royal Veterinary College, London, UK; Oregon State University, Corvallis, Oregon; Oregon State University, Corvallis, Oregon; Royal Veterinary College, London, UK yblum@rvc.ac.uk

We seek to understand the strategies used by animals to achieve stable and robust locomotion in uneven terrain. As stance dynamics are strongly influenced by the landing conditions, a critical transition occurs between the swing and stance phase of the leg. We therefore hypothesize that animals use a simple swing leg control policy to target landing conditions that achieve specific performance goals. In several studies, we investigated the dynamics and kinematics of different bird species (quail, pheasants, guinea fowl, and turkeys) while running over level ground and negotiating a ground height disturbance (such as a step up, step down, or an obstacle). It appears that swing leg control, namely the time-dependent adjustment of leg angle and leg length in anticipation of ground contact, affects the initial conditions of the following stance phase, and therefore, controls the stance phase as well. Especially the angle between the center of mass’ velocity vector and the virtual leg, which determines the amount of leg loading during stance, seems to be critical for stance dynamics. To evaluate the observed behavior, we then developed and analyzed potential swing leg control policies based on principles of disturbance rejection and injury avoidance, applied these control policies to a simple model with a passive stance phase, and compared the predictions to the experimental data. The results suggest a compromise between disturbance rejection and injury avoidance, as birds do not achieve perfect disturbance rejection, but the strategies they use do result in very impressive robust locomotion without exceeding peak forces or impulses that could lead to musculo-skeletal damage. This work was funded by BBSRC and HFSP.