Guineafowl with a twist: asymmetric limb control in steady bipedal locomotion

Abstract

In avian bipeds performing steady locomotion, right and left limbs are typically assumed to act out of phase, but with little kinematic disparity. However, outwardly appearing steadiness may harbor previously unrecognized asymmetries. Here, we present markerbased XROMM data showing that guineafowl on a treadmill routinely yaw away from their direction of travel using asymmetrical limb kinematics. Variation is most strongly reflected at the hip joints, where patterns of femoral long-axis rotation closely correlate to degree of yaw divergence. As yaw deviations increase, hip long-axis rotation angles undergo larger excursions and shift from biphasic to monophasic patterns. At large yaw angles, the alternately striding limbs exhibit synchronous external and internal femoral rotations of substantial magnitude. Hip coordination patterns resembling those used during sidestep maneuvers allow birds to asymmetrically modulate their mediolateral limb trajectories and thereby advance using a range of body orientations.

Gearing effects of the patella (knee extensor muscle sesamoid) of the helmeted guineafowl during terrestrial locomotion

“…We used kinematic data collected during a previous study (Kambic, Roberts & Gatesy, 2015). Only one specimen used in Kambic et al .…”

“…After recovery, the subject was induced to run at 1.6 ms −1 on a motorized treadmill. Videoradiographs of this activity were taken simultaneously from two angles at 250 Hz (see Kambic et al ., 2015 for details, all surgical and experimental techniques approved by Brown IACUC).…”

“…Kinematic data were filtered at 15 Hz (Fourth order Butterworth, low‐pass) in Matlab and used to animate a digital model of the subject in Maya. Joint coordinate systems were added to the hip and knee (See Kambic et al ., 2015 for details), allowing joint angles to be calculated (Fig. 3).…”

“…Joint angle conventions follow Kambic et al . (2015) – hip extension angle is 0° when the femur points cranially, parallel to the wings of the ilium; at a hip angle of 90°, the femur points ventrally. The knee is fully extended at 180°, smaller knee angles are more flexed.…”

“…Upper subfigure shows mean joint angles (see Kambic et al ., 2015) averaged from time‐normalized data from all recorded strides for the hip (solid) and knee (dashed) joints, plotted against percentage stance and swing phases. Values one standard deviation ± from the mean value (thick lines) are shown as thinner lines in the same format.…”