The energy to skate comes from your legs. That means every time you push off you are compressing the springs before you actually go anywhere. And the springs are likely going to be big and add a lot of mass and size to the skates. Skateboards have springs, imagine adding one of those contraptions to a set of inline skates. It would lift you up probably 2-3 inches and make the skate much longer. What does it get you? Not much. They only flex a little, the rest is handled by your knees anyway.
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