Agreed. Knees are fragile, complicated, and their healing is invariably slow(er) than many other foot and leg injuries. (Have had two.) It's not about muscle tissus, and the ice/heat therapy, or massage, or other techniques are often unavailable. Anyone who's had a fall of any kind and not shielded the kneecaps knows what recovery feels like -- two steps forward, literally, and one backward. Actors are known for resiliency, and to play with pain. Especially dancers. But it's hard to imagine a joint more vulnerable to the demands of musical theater, and this role requires enormous range.
"I'm a comedian, but in my spare time, things bother me." Garry Shandling