BOSTON – While president of basketball operations Danny Ainge was hard at work this summer reshaping the Boston Celtics’ roster, Marcus Smart was hard at work reshaping his body.

The tenacious 23-year-old developed a healthy meal plan with his personal chef. He worked out in the gym for several hours per day, every day. And in two month’s time he dropped from a burly, 240 pounds to a fit, 219 pounds.

“It’s a new me. It truly is,” Smart said Wednesday evening during a visit to the Floating Hospital for Children at Tufts Medical Center in Boston. “I’m more explosive and things like that, and I’m healthy … I locked in this summer. I was in the gym every day. Nonstop, every day. I’ve been consistent and I’ve been working my butt off.”

Why did Smart feel the need for a drastic change? Because the fourth-year guard is planning to take on a new role with the Celtics – a leadership role – so he wanted to become a new man.

Smart watched from afar this summer as Boston nearly overturned its entire roster. Three of his teammates from last season’s team were traded, three more were waived and five players left via free agency. Come September, he was one of just four players remaining from the 2016-17 roster, along with Jaylen Brown, Al Horford and Terry Rozier.

On top of that, Smart is now the longest-tenured member of the team – a distinction that was previously held by Avery Bradley, who was traded in July to Detroit in exchange for swingman Marcus Morris.

Smart said that he is honored to take the tenure torch from Bradley, and he has been preparing himself to adopt more of a leadership role this coming season.

“I’ve talked numerous times to Danny and Brad (Stevens) before any [summer transactions] happened, even last year during the season, about being ready,” said Smart, who averaged 10.6 points, 4.6 assists and 3.9 rebounds per game last season. “I’m ready to take on that role. And now it’s put into reality where we don’t have Avery and we don’t have Jae Crowder (traded to Cleveland). A lot more responsibility is on my shoulders.”

Over the years, Smart learned a lot from Bradley and Crowder when it comes to what it takes to be a leader. He also took some notes from Isaiah Thomas, who was traded in late August along with Crowder, Ante Zizic, a future first-round draft pick and a future second-round pick to Cleveland in exchange for Kyrie Irving.

“He’s always played way, way above any limits that anybody has set for him,” Smart said of Thomas. “That’s the type of guy you like to be around. He’s the type of guy that brings energy, he brings positivity, he uplifts people. He has that type of personality where he talks, people listen and he changes lives and he doesn’t even know it.”

Smart admitted that he’s still digesting the trade. He said it “feels unreal” to part ways with guys like Crowder and Bradley, and especially Thomas, who is one of the franchise’s all-time fan favorites.

“I know everybody in this city is going to miss [Thomas],” said Smart. “We love him and we understand the circumstances, but he will never be forgotten.”

Smart will always hold a special place in his heart for his former teammates and mentors, but now it’s time to move onto something new. He’s excited to welcome nearly a dozen new Celtics to the squad, including the four-time All-Star whom Boston received in the IT trade.

“Kyrie is just like Isaiah in a way,” Smart said. “They both bring that type of toughness as smaller guards. They’ve played above everybody’s expectations. Both guys can score the ball very well. Both guys can create their own shots and really dominate a game, especially in the fourth quarter.”

Gaining a player of Irving’s caliber, along with All-Star summer signee Gordon Hayward, should allow Boston to maintain its rank among the NBA’s elite teams this season. And if Smart’s offseason work pays off, he, too, should have an extensive role in leading this team back to a deep postseason run.

Soon, a healthier Smart will have the opportunity to put his offseason work to the test. The reshaped Celtics will be hitting the court for preseason action in less than a month, and their reshaped, fourth-year guard will look to help lead the charge.