Long-axis rotation: a missing degree of freedom in avian bipedal locomotion

摘要: Ground-dwelling birds are typically characterized as erect bipeds having hind limbs that operate parasagittally. Consequently, most previous research has emphasized flexion/extension angles and moments calculated from a lateral perspective. Three-dimensional (3D) motion analyses have documented non-planar limb movements, but the skeletal kinematics underlying changes in foot orientation transverse position remain unclear. In particular, long-axis rotation of proximal segments is extremely difficult to measure with topical markers. Here, we present six degree freedom kinematic data maneuvering guineafowl acquired by marker-based XROMM (X-ray Reconstruction Moving Morphology). Translations rotations hips, knees, ankles pelvis were derived animated bone models using explicit joint coordinate systems. We distinguished sidesteps, sidestep yaws, crossover turns turns, often performed sequence blended partial maneuvers. Long-axis femur (up 38 deg) modulated foot's position. tibiotarsus 65 also affected medio-lateral positioning, primarily served either re-orient swing phase or yaw body about stance foot. Tarsometatarsal was minimal, hip, knee ankle abduction/adduction. Despite superficially hinge-like joints, substantial hips knees execute complex 3D maneuvers while striking diversity poses.