Data from: 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 analyze 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 analyzing synchronously recorded kinematic (3D x-ray videography) and kinetic (3D force measurement) quail locomotion data. Then, by simulating quail gaits using a simplistic bio-inspired numerical model which made use of parameters obtained in in vivo experiments with real quail, we show that the observed asymmetric leg function (reflected in left-skewed ground reaction force and touchdown lift-off limb asymmetry) 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 the quail and most of the other small birds. We hypothesize that stability of bipedal locomotion is a functional demand that, depending on trunk orientation, constrains basic hind limb morphology and function.

与人类直立的躯干不同，大多数鸟类的躯干朝向几乎呈水平前倾（pronograde）状态。不难设想，沉重躯干的朝向会对双足陆地运动的动力学特性产生显著影响。本研究首次分析了前倾躯干朝向对双足运动过程中腿部功能与运动稳定性的影响。为此，本研究通过分析同步采集的鹌鹑运动学（三维X射线摄影）与动力学（三维测力）数据，首先推断出广义小型鸟类在陆地运动时所采用的腿部功能与躯干控制策略。随后，借助从真实鹌鹑活体实验中获取的参数，利用简化的仿生数值模型对鹌鹑步态进行仿真，结果表明：观测到的不对称腿部功能（体现为左偏地面反作用力与触地离地肢体不对称性）是实现前倾躯干稳态运动的必要条件。此外，当匹配特定形态学参数时，稳态运动可获得稳定状态。在采用类鹌鹑参数的情况下，最常见的稳定解为接地奔跑（grounded running），这也是鹌鹑与绝大多数其他小型鸟类偏好的步态类型。本研究提出假说：双足运动的稳定性是一项功能性需求，其会根据躯干朝向的不同，对后肢的基本形态与功能产生约束。