3D Avian bipedal locomotion in even and unpredictable environments: an integrative study of locomotion control, body and leg proportions

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Bipedalism evolved about 230 million years ago in archosaurs, a group that includes crocodilians and dinosaurs, being the most recent ancestors of modern birds. Today there exist nearly 10,000 bird species. Many of them are likely well adapted for terrestrial locomotion, use walking and running gaits, but also other gaits such as grounded running (running without aerial phases) or mixed gaits (a combination of walk and run). Across such a great number of species within birds, there is, in addition, considerable variation in hindlimb morphology relating to differences in ecology and biomechanical demands. Morphological adaptations of limb segments influence both the motions of whole limb and the relative motion of the limb segments to one another during terrestrial locomotion. Birds provide a natural animal model for understanding the functional demands of striding bipedalism and how these demands change with body size or leg segment proportions. The goals of the present scientific proposal is to bring light about the following questions: i) What are the constructive (morphological) proportions which still assure stable locomotion? ii) How do ecological and biomechanical factors influence avian hindlimb design and how this design constrains feedforward and feedback control during even and perturbed locomotion? iii) How do birds control their pronograde trunk during perturbed locomotion? iiii) Can leg segment length and kinematics be predicted? To approach these questions, I aim to combine full 3D-experiments (involving synchronously measurement of X-ray fluoroscopy, ground reaction forces and muscle activation) with numerical simulations. Experiments will allow me to compute a very precise 3D inverse dynamics on even, rough and unpredictable terrains. By using electromyography, I will investigate muscular preparation and activation strategies prior to touch down and during contact when negotiating a hurdle or a hole and their relation to leg geometry. Experiments will also deliver template (model) related trunk and leg strategies to negotiate with rough terrain, which will be tested in numerical simulations. Numerical simulations will also help me to investigate which are the constructive (morphological) features that assure self-stable locomotion in birds and dinosaurs. I aim to explain avian body proportions and leg segment proportions based on stability and energy minimization. Also I expect to uncover how trunk balance and leg proportions influence the ability to navigate on terrestrial environments with uneven and irregular terrain. The developed experimental and simulation methods may help to predict gaits, locomotion speeds and segment kinematics of extant and extinct bipeds and may also impulse new design paths in bio-inspired robots.