"You won't stop running," says Alex, as if that explains everything. He doesn't throw any more ice, though, despite having a clear shot until J runs into the room. Is that a flicker of doubt?

...a second later he's sure that no, it wasn't, because hah, doubt? What's doubt?

Alex chases J through the door, gradually closing the gap between them. See, he's been flat-out racing. But he hasn't been conserving his energy, and it'll catch up to him soon. Just because he feels superhuman doesn't mean he is.