Seeing as i'm 59 and never been in a Gym since I left school in 1969, what's so impressive about it? Genuine question
They've created a vacuum where the injury is and simply put, created space. If you look carefully you can see little moons and stars.
To give you a serious answer, the anti-grav basically alleviates the pressure on the injured leg, so he's able to run, and gradually put more weight on it as he progresses with rehab. See it a lot with Aussie Rules players down here.