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Compliance & Coordinated Landing
How does surface stiffness affect landing behavior? To test this we had toads hop onto a platform I constructed that could freely move up and down while being attached to different springs or locked in place to change the platform's stiffness. We measured the toad's impact forces and tracked each joint of the forelimb using high-speed video. With this data we could then calculate how much work each joint did to slow the toad down upon impact. We found that cane toads stick the landing across a wide range of surface stiffness but they do tend to use their elbow more on rigid surfaces while their shoulder puts in more effort on compliant surfaces. Additionally, the overall energy required by the toads to slow themselves decreases on compliant surfaces - which helps explain why trampolines are easier and fun to jump on but hopping on concrete is more of a workout. |
Above are examples of the same toad landing on a rigid surface (left) and the most compliant surface (right; 10 mm of displacement per body weight).
The top plots is the limb extension ratio (LER; in magenta) throughout landing, where a LER of 1 would be the arms fully stretched out and a value of 0 having the hands flexed up against the chest.
The middle plots show the magnitude of the ground reaction force (GRF; in blue) and the displacement of the platform (orange).
The bottom plots are the instantaneous joint powers for the wrist, elbow and shoulder joints.
The top plots is the limb extension ratio (LER; in magenta) throughout landing, where a LER of 1 would be the arms fully stretched out and a value of 0 having the hands flexed up against the chest.
The middle plots show the magnitude of the ground reaction force (GRF; in blue) and the displacement of the platform (orange).
The bottom plots are the instantaneous joint powers for the wrist, elbow and shoulder joints.
Next Step
After figuring out that cane toads use muscles in the shoulder joint to slow themselves down when landing on compliant surfaces I became interested in how cane toads may be modulating their muscle activity in preparation for and during landing. Click here to learn more about my second chapter which addressed this question.
After figuring out that cane toads use muscles in the shoulder joint to slow themselves down when landing on compliant surfaces I became interested in how cane toads may be modulating their muscle activity in preparation for and during landing. Click here to learn more about my second chapter which addressed this question.
