"He's a hard worker," [defensive line coach John] Mitchell said of Heyward, drafted with the 31st overall pick. "What he's realizing now is, he might have been in shape to play at Ohio State, but he's not in shape to play in the NFL. There's a big difference. That slowed him down for the first couple days, but he's getting in better shape. You can see some of the quickness he has. And he's learning how to play with strength."
It's not entirely clear what "shape" means here, or why it would only take a couple days to improve it dramatically, but it sounds like he's trying to adjust to the increased speed and physicality of the game, which is tough for most rookies. That's probably especially true given that the lockout just ended a couple weeks ago.
Mitchell also notes that Heyward's fellow defensive end Ziggy Hood is "going to play quite a bit," which is no surprise, since Hood played a lot, and played well, while filling in last year. Even if Aaron Smith and Brett Keisel stay healthy this year, it's hard to imagine Hood sitting on the sidelines for too long.