Well, my answer will gcount towards a grasshopper...
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Well, Grasshoppers have 3 pairs of jointed legs. The first 2 pairs of smaller legs are used for walking and climbing... while as for the 3rd pair of hind legs, they are adapted for jumping....
So basically, when the Grasshopper jumps, the flexor muscles contracts, bringing the hind legs to this 'Z' position (in which the hind legs are folded and appeared like the letter 'Z'). The extensor muscles will then contract while the flexor muscles relax (producing a powerful force to push against the ground) and therefore, it propels the grasshopper into the air. This mechanism is called jumping.