It’s two minutes into a January regular-season game for the Celtics, and the team’s new big man, Al Horford, is defending Utah’s 6-foot-8 guard Rodney Hood more than 20 feet away from the hoop. With nobody else near, the advantage is Hood’s, if he can use his speed to move past Horford for an easy layup. A big man defending a quicker guard is a matchup all offenses want, and the 24-year-old Hood has it. But Horford is not your average big man. He’s got agility, smoothly sliding his feet toward the hoop, staying in front of Hood and forcing him into an off-balance 10-foot shot that misses. He’s got speed, and when the rebound is grabbed by Boston, Horford swiftly makes his way up the court, passing four Utah defenders as he runs more than 80 feet in a matter of seconds. And he’s got strength, corralling a pass about 8 feet from the hoop and slamming home a dunk for two points. It’s a four-point swing in a game the Celtics would go on to win.

The dunk shows up in highlights the next day, but it’s those complete plays on both ends of the court that led the Celtics to sign Horford to a 4-year, $113 million contract in July. And the agility, speed and strength that the 6-foot-10-inch Horford displayed on that play are some of the reasons the Celtics are betting that the 30-year-old—who’s surrounded by mostly 20-something teammates—is still near the peak of his basketball powers. Staying in shape is essential for the four-time All-Star, who’s been working hard off the court for nearly his whole life with a focus on fitness and nutrition. He’s garnered a number of different mentors along the way, but none more important than his first one. His father, Tito, was a professional basketball player, and 7-year-old Al would observe him lifting weights and working on conditioning.

Photo: Brian Babineau / Boston Celtics

“I wasn’t doing the lifting, but I would go running with him around the stadium and do sprints with the team while they were running,” Horford recalls. “From an early age, I had an understanding of what it took to work.”

Horford knew he had to hit the weight room to succeed on the court, and he saw results early in his career, winning two national championships in his three years at the University of Florida. Drafted by the Atlanta Hawks in 2007, he was picked as an All-Star twice in his first four years in the NBA. But a setback came in his fifth season when he played only 11 games before tearing his left pectoral muscle, an injury that cost him the rest of the regular season. It was in that summer of 2012 that Horford met Kenny Atkinson, who joined the Hawks as an assistant coach. Atkinson convinced Horford that it wasn’t simply about working hard; it was about working smart.

Photo: John Huet; Grooming: Lori Greene / Ennis Inc.

“[Kenny’s] a big fitness guy, and when he got the job with the Hawks, there would be some days when we would train really hard on the court, we’d go do some things in the weight room, we’d do some conditioning. And then the next day, I’d come in expecting the same thing, and he’d say, ‘No, today is a lot lighter,’” Horford recalls. “I just noticed that my performance would get better in games because we knew when to push and when to back off. Sometimes we backed all the way off.”

That 2012-13 season saw Horford establish new career highs in minutes, rebounds, steals and points per game. Some days, his workout would be as little as a 45-minute treadmill walk at 3 mph on a 12 percent incline. It wasn’t just Atkinson’s influence, however, that helped Horford. He also credits Kyle Korver, who joined the Atlanta team that same season, for helping him strive even further in fitness. After his 2013-14 season was cut short with a torn right pectoral muscle, Horford turned an even sharper focus on smarter training and recovery. These days, he’s fond of spending 7 to 10 minutes at a high setting on a VersaClimber, which mimics climbing. And for recovery he’ll spend time in a cold tub or using NormaTec boots to massage his legs.

Photo: Steve Babineau / Boston Celtics

“I’m usually doing stuff like that every day… I’m not a fan of being on a machine for an hour or running outside for an hour. It’s all about getting your heart rate up,” Horford says. “During the season, cardio and flexibility are the most important. It’s more about maintaining my strength. Cardio would be 50 percent [of my time]. Flexibility would be 30 percent, and strength is 20.”

“Flexibility” is important in more than just the physical sense of the word. After nine years in the Hawks organization, the transition to the Celtics’ way of doing things this summer could have marked a challenging change. But Horford was ready to adapt, and longtime Celtics strength and conditioning coach Bryan Doo was more than accommodating for the newest Celtics star, whose wife, Amelia (2003’s Miss Universe), would eventually give birth to their second child in November.

“As soon as we signed him, the training staff spent six or seven weeks down there with them. His wife was pregnant, so he was going to try to move up, but he couldn’t because he wanted to be with his wife, which makes sense,” Doo says. “So we’d go down for four to five days, and have the weekend off, for about seven or eight weeks. It was good because that first conversation was ‘Hey Al, look, tell me what your experience with fitness is, what you want to gain over the next five years and what your goal is.’ ”

Doo had gotten a rundown from the Atlanta staff on Horford’s workouts, and he had heard the imposing frontcourt player was open to trying new techniques. Doo watched some film on his own to see if he could find any aspect of Horford’s game to improve, and he found one: Horford’s lateral movement.

“He’s good at it, but I think his position needs to be lower. He’s worked on it, and I think for him, just making small workout changes to how he pushes and what muscles he uses have helped him,” Doo says. “He says, ‘It’s interesting, since we started doing those drills, I’m actually less tired when I’m pushing.’ [We’re also working on] bending his leg a little better when he’s going to the hoop to dunk. Little things like that.”

Doo sets a monthly calendar of workouts for Horford, but he says he’ll change it depending on how Horford’s feeling: “We check in every day, and if his hip’s bothering him, we’ll work on his hip. And so forth. It’s a really good relationship. He’s really easy to work with.”

Photo: Brian Babineau / Boston Celtics

Horford also still hears from his dad via text after games, with specific tips on cardio for the next day. But Al points to the nutrition habits he learned from his father as being the other main factor for maintaining the same 245-pound frame that he’s had since college.

“It’s about eating things with purpose and maybe eating certain carbs before you play so you have more energy. Most of what I drink is just water,” Horford says. “Water is all I consume 95 percent of the time.”

For what to eat when he’s not chugging water, Horford has also sought advice from a familiar face for Boston sports fans: a certain superstar quarterback in Foxborough. A year before Horford ever donned Celtics green—and a year before Tom Brady helped the Celtics unsuccessfully woo Kevin Durant—Horford traveled to the TB12 headquarters at Patriot Place to meet with Brady and his health guru Alex Guerrero.

“I was with the Hawks obviously, and I went out in the summer. I spoke to Alex and met with Brady briefly and talked about some of his habits and his focus. It was great for me. I have a lot of respect for those guys and what they do. It really helped me for what I needed to do for my career,” Horford says. “Those guys are a little on the extreme side. They’re very particular, but I definitely agree with a lot of the things they’re about.”

Horford hasn’t gone as far as stocking up on spirulina or some of the other staples of the strict Brady diet. Instead, it’s more about staying away from as many bad foods as possible. That means no fried foods, no juice or drinks with additional sugar. He jokes that he’ll break and eat ice cream about once or twice a year, but usually in the offseason (and it’s not avocado flavored!). During the season, Horford sticks to a routine. On gamedays, it’s a big breakfast: usually sourdough bread, a salad and eggs. For lunch, the Dominican native goes with traditional food from his home country: rice and corn, some grilled chicken, sweet plantains and avocado. “It’s lots of good carbs, but it also gives you good energy and some good fats from the avocado,” he says. His pregame snack is oranges. And his halftime treat? Applesauce. “It usually gets my sugar going, and it holds me till after the game.”

Photo: Brian Babineau / Boston Celtics

While Doo laughs off the applesauce habit, he raves about Horford’s nutrition, and what he hopes is a trickle-down effect on the rest of the Celtics players.

“His nutrition is unreal. He eats so well. He’s a great influence in the locker room. Young guys look at him and say, ‘Wow,’ ” Doo says. “You can just see them watching him eat, and hopefully they’ll put it together that it can create a long career.”

Doo is the latest in a lifetime of voices Horford has listened to while seeking to take care of his body and improve his on-court performance. In his 10th season in the NBA, and his first with the Celtics, Horford is averaging a career high in blocks, 3-pointers made and assists, while pushing Boston closer to the league’s elite teams. From seasons spent with Atkinson and Korver to a meeting held with Brady and Guerrero, Horford will draw on many different bits of advice as he works to maintain his body during his 30s. But it’s his first mentor—his dad—whose voice still resonates with him the most.

“He’s big on doing stuff off the court to get you ready for the next challenge on the court. That’s literally his go-to line,” Horford says.

Consider it message received.