Trunk orientation causes asymmetries in leg function in small bird terrestrial locomotion

The ostrich (Struthio camelus) is widely appreciated as a fast and agile bipedal athlete, and is a useful comparative bipedal model for human locomotion. Here, we used GPS-IMU sensors to measure naturally selected gait dynamics of ostriches roaming freely over a wide range of speeds in an open field and developed a quantitative method for distinguishing walking and running using accelerometry. We compared freely selected gait-speed distributions with previous laboratory measures of gait dynamics and energetics. We also measured the walk-run and run-walk transition speeds and compared them with those reported for humans. We found that ostriches prefer to walk remarkably slowly, with a narrow walking speed distribution consistent with minimizing cost of transport (CoT) according to a rigid-legged walking model. The dimensionless speeds of the walk-run and run-walk transitions are slower than those observed in humans. Unlike humans, ostriches transition to a run well below the mechanical limit necessitating an aerial phase, as predicted by a compass-gait walking model. When running, ostriches use a broad speed distribution, consistent with previous observations that ostriches are relatively economical runners and have a flat curve for CoT against speed. In contrast, horses exhibit U-shaped curves for CoT against speed, with a narrow speed range within each gait for minimizing CoT. Overall, the gait dynamics of ostriches moving freely over natural terrain are consistent with previous labbased measures of locomotion. Nonetheless, ostriches, like humans, exhibit a gait-transition hysteresis that is not explained by steady-state locomotor dynamics and energetics. Further study is required to understand the dynamics of gait transitions.

Section: Data Processing and Gait Measurementmentioning

confidence: 99%

Preferred gait and walk–run transition speeds in ostriches measured using GPS-IMU sensors

Daley

Channon

Nolan

et al. 2016

“…Despite the different morphology of human and bird legs, in both walking and running, the function of the virtual leg can be described with surprisingly simple phenomenological gait models (Maus et al, 2010;Andrada et al, 2014). In a system including a trunk with inertia, the human leg function could be approximated with a spring-like telescopic leg and hip torques that keep the trunk upright (Maus et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…A spring-like axial leg function may result from compliant muscles and properly adjusted muscle activation (Geyer et al, 2003). However, when modelling the pronograde locomotion of birds, the spring describing the compliant axial leg function (leg length and force in leg direction) was complemented by axial damping to successfully explain the axial kinetic and kinematic asymmetries induced by trunk orientation (Andrada et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Increasing trunk flexion morphs human leg function into that of birds despite different leg morphology

Aminiaghdam

Rode

Müller

et al. 2016

Self Cite

Pronograde trunk orientation in small birds causes prominent intra-limb asymmetries in the leg function. As yet, it is not clear whether these asymmetries induced by the trunk reflect general constraints on the leg function regardless of the specific leg architecture or size of the species. To address this, we instructed 12 human volunteers to walk at a self-selected velocity with four postures: regular erect, or with 30 deg, 50 deg and maximal trunk flexion. In addition, we simulated the axial leg force (along the line connecting hip and centre of pressure) using two simple models: spring and damper in series, and parallel spring and damper. As trunk flexion increases, lower limb joints become more flexed during stance. Similar to birds, the associated posterior shift of the hip relative to the centre of mass leads to a shorter leg at toe-off than at touchdown, and to a flatter angle of attack and a steeper leg angle at toe-off. Furthermore, walking with maximal trunk flexion induces right-skewed vertical and horizontal ground reaction force profiles comparable to those in birds. Interestingly, the spring and damper in series model provides a superior prediction of the axial leg force across trunk-flexed gaits compared with the parallel spring and damper model; in regular erect gait, the damper does not substantially improve the reproduction of the human axial leg force. In conclusion, mimicking the pronograde locomotion of birds by bending the trunk forward in humans causes a leg function similar to that of birds despite the different morphology of the segmented legs.

“…Birds are predominantly studied moving forward over level ground at relatively constant speeds in both kinematic (Cracraft, 1971;Jacobson and Hollyday, 1982;Muir et al, 1996;Gatesy and Biewener, 1991;Gatesy, 1999a;Abourachid, 2000Abourachid, , 2001Reilly, 2000;Verstappen et al, 2000;Rubenson et al, 2007;Nyakatura et al, 2012;Provini et al, 2012;Stoessel and Fischer, 2012) and kinetic (Clark and Alexander, 1975;Alexander et al, 1979;Roberts et al, 1998;Hancock et al, 2007;Goetz et al, 2008;Nudds et al, 2010;Rubenson et al, 2011;Andrada et al, 2013Andrada et al, , 2014 analyses. Compared with the uniformity of locomotion on a treadmill or straight trackway, the inherent variability of unsteady behaviors is much more difficult to characterize.…”

Section: Introductionmentioning

confidence: 99%

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

Kambic

Roberts

Gatesy

2015

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.