Trunk orientation causes asymmetries in leg function in small bird terrestrial locomotion.
In contrast to the upright trunk in humans, trunk orientation in most birds is almost horizontal (pronograde). It is conceivable that the orientation of the heavy trunk strongly influences the dynamics of bipedal terrestrial locomotion. Here, we analyse for the first time the effects of a pronograde trunk orientation on leg function and stability during bipedal locomotion. For this, we first inferred the leg function and trunk control strategy applied by a generalized small bird during terrestrial locomotion by analysing synchronously recorded kinematic (three-dimensional X-ray videography) and kinetic (three-dimensional force measurement) quail locomotion data. Then, by simulating quail gaits using a simplistic bioinspired numerical model which made use of parameters obtained in in vivo experiments with real quail, we show that the observed asymmetric leg function (left-skewed ground reaction force and longer leg at touchdown than at lift-off) is necessary for pronograde steady-state locomotion. In addition, steady-state locomotion becomes stable for specific morphological parameters. For quail-like parameters, the most common stable solution is grounded running, a gait preferred by quail and most of the other small birds. We hypothesize that stability of bipedal locomotion is a functional demand that, depending on trunk orientation and centre of mass location, constrains basic hind limb morphology and function, such as leg length, leg stiffness and leg damping.
Science of Motion, Friedrich-Schiller University Jena, Seidelstraße 20, 07749 Jena, Germany emanuel.andrada@uni-jena.de.
Emanuel
E
Andrada
Science of Motion, Friedrich-Schiller University Jena, Seidelstraße 20, 07749 Jena, Germany.
Christian
C
Rode
Science of Motion, Friedrich-Schiller University Jena, Seidelstraße 20, 07749 Jena, Germany.
Yefta
Y
Sutedja
Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität, 07743 Jena, Germany Image Knowledge Gestaltung: an interdisciplinary laboratory and Institute of Biology, Humboldt-University, Philippstraße 13, 11015 Berlin, Germany.
John A
JA
Nyakatura
Science of Motion, Friedrich-Schiller University Jena, Seidelstraße 20, 07749 Jena, Germany.
Reinhard
R
Blickhan
D000818:Animals; D003198:Computer Simulation; D005121:Extremities / Q000502:physiology*; D008124:Locomotion / Q000502:physiology*; D011187:Posture; D011784:Quail / Q000033:anatomy & histology / Q000502:physiology*
avian locomotion; biomechanics; leg function; pronograde locomotion; stability