Question

in fact, while testing out the new designs, he was climbing better and faster in his prosthetics than he ever had with his biological legs. the experience changed the way he thought about prosthetics and athletics.
reread the sentence from the passage
the experience changed the way he thought about prosthetics and athletics.
what does the phrase the experience refer to?
changed the way he thought about prosthetics and athletics.

Explanation:

The previous - sentence describes Mark testing new prosthetic designs and climbing better with them than with his biological legs. This specific event is what "the experience" refers to.

Answer:

Mark climbing better and faster in his prosthetics than with his biological legs while testing new designs.