Three days after New Jersey Gov. Chris Christie called California Gov. Jerry Brown an “old retread,” the Democratic governor fired back on Thursday, challenging Christie to a physical fitness contest.

“There’s nothing wrong with being a little retread,” the 74-year-old, third-term governor told members of the United Food and Commercial Workers Local 770 in Los Angeles. “Not as much hair, I’m slowed down a little bit. But I have to tell you, I ran three miles in 29 minutes two nights ago … and I hereby challenge Gov. Christie to a three-mile race, a pushup contest and a chin-up contest. And whatever he wants to bet, I have no doubt of the outcome.” …

Brown said Christie’s attack was “the first time I’ve ever been attacked at a convention, so I feel that I’ve finally come into my own, that I’m being attacked by the Republicans.”