TAMPA, Fla. — Is it fat? Is it muscle? Yankees general manager Brian Cashman won't say, except he too has noticed Joba Chamberlain's weight gain.

"He's heavier," Cashman said, though he refused to elaborate.

Chamberlain, who is noticeably more filled out in his chest and shoulders, has said that the weight gain is muscle.

"I feel great, I’m stronger physically," said Chamberlain, who also declined to offer specifics. "I’m better in my bullpens."

Cashman says he knows how much weight Chamberlain has gained, though he refused to share.

"He's not the only one," Cashman said, of others who have reported to camp with extra weight.

Yankees manager Joe Girardi said Chamberlain will be evaluated on his performance. So far, Girardi said Chamberlain has thrown the ball well in his bullpens and has had no issues with any conditioning drills.

Marc Carig: mcarig@starledger.com