There were no backpacks or teachers, but the warm greetings on Monday morning harkened defensive tackle Calais Campbell back to his classroom days.

A vast majority of players showed up for the beginning of the voluntary strength and conditioning workouts at the Cardinals' training facility, kickstarting the offseason program. Smiles and handshakes were abundant as the team reconvened in the weight room after a few months apart.

"It's like the first day of school," Campbell said. "Everybody saying what's up to each other, 'Where you been at? How you been?' The only thing that's different is nobody has those back-to-school outfits. Everybody's in shorts and T-shirts still. It's a good time, though."

The schedule allows for two hours of working out and two hours of classroom time during this initial phase, and for a group which made the NFC Championship game last season, it couldn't come quickly enough.

"It's always a long offseason," quarterback Carson Palmer said. "(The season) ends, and then you start getting back in the gym and getting ready, preparing your body and preparing your mind. Then you still have another month or so to go. We're at the point now where guys have been preparing for this and getting ready to get back in here and start thinking about this upcoming year. It's just good to see everybody again and get back to work."

There were many familiar faces working out together and a collection of new ones. Safety Tony Jefferson, wide receiver Jaron Brown and safety D.J. Swearinger were present after signing their restricted free agent tenders prior to the workout. Guard Evan Mathis, outside linebacker Chandler Jones and safety Tyvon Branch were the most prominent offseason additions and were all on hand.

Monday began a two-week phase of only strength and conditioning and will be followed by the second phase, which allows for three weeks of on-field workouts. Organized team activities will begin on May 17, with minicamp in June.

Jones learned late last week that he will face his former team, the Patriots, in the season opener on "Sunday Night Football." He was traded to the Cardinals for guard Jonathan Cooper and a second-round draft pick last month.

"That's exciting," Jones said. "I won't have to wait long."

Mathis won a Super Bowl last season with the Broncos, one of only a few players on the roster to reach the sport's pinnacle. He said he was looking forward to joining Denver last season knowing it was on the precipice of a championship, and feels the same way this year about the Cardinals after their deep postseason run of 2015.

"That experience, it does wonders for the team," Mathis said. "I'm looking forward to working with a bunch of guys who are hungry to go make it happen."

Count Palmer among the hungriest. He had to grind through knee rehabilitation last season, and even though he ended 2015 relatively healthy, he hasn't taken things any easier this offseason.

"There's kind of a falsity that people think that the older you get, the less you train," said Palmer, 36. "It's actually the opposite. The older you get, the harder you train."

This is just the start of the offseason, and there are still months to go before any meaningful action on the field, but to the Cardinals, it was an encouraging beginning.

"I don't how if other teams take it as seriously as we do, but we take the offseason program very seriously," Campbell said. "This is what sets you apart from everybody else, making sure you're in better shape and stronger."