OXNARD, Calif. -- It's Day 3 of Cowboys training camp, which means training camp is really here because the players will be in pads for the first time.

The pads come on: NFL rules prevent teams from wearing pads the first two days of camp, so today’s three-hour session should be popping.

“Usually from my past experience the attitudes in the locker room change,” linebacker Dan Connor said. “Everybody gets a little more serious. It’s more like a game environment … Once you throw them on it raises up the level and guys know you’ve got to be precise mentally and be precise physically on every play.”

With the pads comes aggravation, which can lead to some heated exchanges between players. Coach Jason Garrett doesn’t want the players getting into scrapes with each other because the work suffers.

Marathon men: Running back Felix Jones, safety Brodney Pool and wide receiver Andre Holmes will get their second crack at running the conditioning test after flunking it on Sunday.

They have opened camp with some “remedial running,” as Garrett has called it.

In order to be cleared for practice they will have to run two sets of 10 60-yard sprints in eight seconds or less, and they will have a short break between the sprints to rest.

Arkin getting look at center: The Cowboys are thin behind starter Phil Costa with Bill Nagy out with a high ankle sprain and Kevin Kowalski on the physically unable to perform list with an ankle injury, so guard David Arkin is getting a look.

Arkin said he has never played center before taking a handful of snaps Tuesday. He did OK. Stephen McGee dropped one shotgun snap, but that was more on the quarterback than Arkin.