BOSTON — While the rest of the NBA was locked out, the Boston Celtics were locked in.

The Big 3 and Rajon Rondo, who led Boston to its unprecedented 17th NBA championship in 2008, were already signed and ready for another run at the title. So while the defending champion Dallas Mavericks were trying to replace Tyson Chandler and Chris Paul was trying to figure out which side of the Staples Center to report to, the Celtics were simply resting up for the season to start.

“It does help, having the five guys back,” coach Doc Rivers said, throwing center Jermaine O’Neal into the mix with Rondo and the Big 3 of Paul Pierce, Kevin Garnett and Ray Allen.

The lockout that wiped out the first seven weeks of the season has widely been seen as a gift to the aging Celtics, who would benefit from the extra time off and the shortened season. But because the 66-game schedule has been compressed, with fewer off-days and frequent strings of three games in four nights, the labor strife may not have done the team any favors.

“We’re all figuring it out. It’s going to be a period where everybody’s adjusting,” Garnett said. “This year will test everybody’s endurance and their willingness. This will be more mental than physical.”

That might not be the best news for the Celtics, who will be relying on the 34-year-old Pierce, 35-year-old Garnett and 36-year-old Allen. O’Neal, 33, is the center for as long as he can stay on the court; he played in only 24 games last season. At least the Celtics don’t have to worry about 39-year-old Shaquille O’Neal, who retired after spending most of last season trying to recuperate from injuries.

“It’s not going to come down to age, but who’s mentally tougher,” Jermaine O’Neal said. “Who’s going to stay mentally tough from the get-go? And also health is a big part of it. You’ve got to take care of your body. My goal is to stay healthy. I just don’t want to be hurt.”

Although the compressed schedule has some teams playing on three consecutive nights, the Celtics will not play back-to-back-to-back games this season. What they do have is a 12-day, eight-game road trip in March to California, Denver, Atlanta, Milwaukee and Philadelphia.

“I don’t know what the impact is of the 66” game schedule, Rivers said.

Garnett said the Celtics’ age can be an advantage.

“The league is getting younger,” he said. “We’re a veteran team, but one thing you can’t teach is experience. We’re a very confident group, a group that’s willing to work.”

Jeff Green, one of the team’s best young players, is already out for the season after surgery to repair an aortic aneurysm. The key piece in the trade that sent Kendrick Perkins to the Oklahoma City Thunder — a deal that likely doomed Boston’s playoff hopes last year, Green is expected to recover and be back next season.

That leaves Marquis Daniels and Sasha Pavlovic backing up Pierce. Brandon Bass replaces Glen “Big Baby” Davis and Keyon Dooling is at backup point guard instead of Delonte West and Nate Robinson. First-round draft pick JaJuan Johnson, the Big Ten defensive player of the year at Purdue last year, joins the front court.

“I like the guys that we brought in,” Pierce said. “I thought a year ago we had a lot of immaturity with our bench roster, and it brought inconsistent play with them. But I think these guys are a lot more experienced, bring a lot more professionalism on a day-to-day basis. I think they’re going to be great.

“And we’re going to need them. Because the season, with the back-to-backs, the games crammed in in such a short period of time, we’re going to be asking a lot of them.”

Rivers said he will try to counter his players’ age by managing their minutes. He would like to get Garnett down to about 30 minutes per game, a number he has hit just once since his rookie season. After averaging close to 40 for most of his years in Minnesota, he played 32.8 minutes a game when he won a championship in his first year with the Celtics in 2008.

Allen has shown no signs of slowing down: He had career bests in field goal (.491) and 3-point shooting (.444) percentage last season.

Pierce is merely hoping he can keep up.

“Right now my motivation is to play longer than Ray. I think he’s going to play another five years. I don’t know if I’ll make it, but he’s definitely been my inspiration, just the way he’s been consistently great even at his age of 42,” Pierce said, smiling. “It’s just amazing. He’s just a genetic wonder.”