S2: Supplementary movie of a live flamingo trial from Mechanical evidence that flamingos can support their body on one leg with little active muscular force

This file contains a MP4 video showing a notable ~20-minute live trial with a bird exhibiting awake behaviors and eventually falling asleep

Hypothesized models of optimal task-level control.

<p>Hypothesized models of optimal task-level control.</p

Kinematic and kinetic constraints used in the optimal control models.

<p><i>A:</i> Kinematics of the musculoskeletal model parameterized to cat bi at four stance distances. LH, left hindlimb; LF, left forelimb; RF, right forelimb; RH, right hindlimb. <i>B:</i> average forces and moments at the CoM in each perturbation direction. Solid lines indicate experimental data, dashed lines indicate task-level constraints used in models MMe, MMm, SMe, SMc. <i>C:</i> average displacement of the CoP in each perturbation direction. Solid lines indicate experimental data, dashed lines indicate task-level constraints used in model MPe.</p

Experimental postural perturbation paradigm and example data used for model constraints and validation.

<p><i>A:</i> Directions of translational perturbations are evenly-spaced in the horizontal plane. <i>B:</i> Coordinate system for forces and kinematics. <i>C:</i> Time traces of platform position, CoM and CoP displacement for a 60° perturbation along the direction of the perturbation, and left hindlimb ground reaction forces for 20 perturbations (cat bi) in the preferred postural configuration. The shaded region represents the initial period of active force generation due to the postural response. The CoM and CoP values in the time bin shown were used to define constraints on performance of the quadrupedal model, and individual forces across the four limbs were then compared to model predictions.</p

Observed and predicted changes in muscle tuning curve magnitude and direction across postural configurations.

<p><i>A:</i> Comparison of muscle tuning curve magnitude scaling across postural configurations observed in cat bi with scaling predicted by models MMm, SMe, and SMc. Data points for individual muscles are shown as filled circles. <i>B:</i> Comparison of muscle tuning curve peak direction shift across postural configurations observed in cat bi with direction shifts predicted in models MMm, SMe, and SMc. Note that although SMc predicted increased tuning curve shifting compared to MMe, none of the models predicted significantly increased shifting compared to experimental data. ns, p>0.05; *, P<0.05; ANOVA, post hoc tests.</p

S1: Supplementary movie of cadaveric flamingo demonstration from Mechanical evidence that flamingos can support their body on one leg with little active muscular force

This file is a MP4 video demonstrating one-legged bodyweight support in a flamingo cadaver specimen

Predicted horizontal plane forces obtained by controlling experimentally-derived muscle synergies versus individual muscles.

<p>Top to bottom: average horizontal-plane forces observed in each postural configuration of cat ni (black), predictions of models controlling individual muscles: MMe (green), or muscle synergies: SMc (blue), and SMe (purple). Arrows highlight significant force magnitude reductions observed in data, SMc, and SMe, but not in MMe.</p

Schematic of variations in muscle activity and limb forces with altered stance distance during balance tasks in cats hypothesized to arise from neuromechanical interactions.

<p>Top to bottom: sagittal-plane kinematics, left hindlimb ground reaction forces, left hindlimb muscle tuning curves. As stance distance between the fore- and hind-limbs is decreased from left to right (top row), a wider range of ground reaction force directions is observed (middle row), as well as increased muscle activation; however, muscle tuning to perturbation direction is conserved (bottom row).</p

Limb forces predicted by optimal task-level control of CoM force and moment.

<p><i>A:</i> average horizontal plane forces observed in each postural configuration of cat bi (black) compared with model MMe predictions (green). Force vectors are drawn for each limb (clockwise from top left: LF, left forelimb; RF, right forelimb; RH, right hindlimb; LH, left hindlimb) with their origins offset in the direction of platform motion. Stance distance decreases from left to right. Predicted forces were directed towards and away from the CoM, characteristic of the force constraint strategy described previously <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002465#pcbi.1002465-Macpherson2" target="_blank">[18]</a> at longer stance distances (34 and 27 cm), whereas a wider range of force directions was observed at shorter stance distances (13 cm) <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002465#pcbi.1002465-Macpherson3" target="_blank">[53]</a>. <i>B:</i> comparison of average and predicted limb force components in polar coordinates. HF, horizontal force; VF, vertical force. Predicted horizontal plane forces reproduced the region of invariant force directions for perturbation directions that unloaded the hindlimb (180° to 270°) observed at longer stance distances (34 and 27 cm) (arrows).</p

S3&S4: Supplementary figures of disarticulated flamingo hip joint; and flamingo museum specimen from Mechanical evidence that flamingos can support their body on one leg with little active muscular force

This file contains images of a disarticulated hip joint from a dissected flamingo carcass showing the relative association of the bony and cartilaginous features of the pelvis and proximal femur (S3). Additional images from a disarticulated flamingo museum specimen showing the prominent features of the knee joint (S4)