A theory about EG Rainbow Dash's super speed · 11:24pm Oct 7th, 2020
What if Rainbow Dash achieves super speed not by going very fast, but by simply slowing the passage of time in her frame of reference??
The MV for Run to Break Free heavily implies this.
So it's not her legs are somehow "supercharged" to go fast. Her magical geode somehow slows the surrounding time around her while she goes at normal jogging speed, which makes her go fast relative to her surroundings.