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Other people point out shoes, but there's also these contraptions that are basically springs / elastics inspired by kangaroos; I had to google a few times, but their common name seems to be "jumping stilts" [1]. There's also more compact variants, jumping boots, that look like leaf springs underneath skeeler / ice skating boots [2]

[1] (no affiliation) https://www.amazon.com/Air-Trekkers-Exercise-Entertainment-P...

[2] https://www.amazon.com/Jumping-Shoes/s?k=Jumping+Shoes

There are, in fact, such shoes, and they do provide what has been called an unfair advantage in track sports.

I mean, springs would do that. Maybe a latch with slightly delayed release mechanism would work better to time the energy release for optimal running. But unless you want to violate conservation of energy (like flubber presumably does) then springs would get you there.

That is actually already a thing, and yes they do provide a significant advantage.