Lisa Burkhalter can’t point to one specific moment when it finally clicked, but when looking back at her life she recalls many.

She thought about it while watching “The Biggest Loser” and polishing off a thick bowl of ice cream as she rooted on her favorite participants. She questioned it when looking back at old pictures, especially one of her and her family at a college football game. And she pondered it at length as she witnessed squatty men and women hobble onto scooters and glide past her in the grocery store.

She had to make a change in her life before it was too late. And it — her obesity — had to be stopped.

“I was just under 250 pounds. I was big, and I just looked at that and I thought, I don’t want that to be me,” she said. “That’s not the life I want.”

So Burkhalter began to make small changes. She started walking, slowly at first, before picking up to a speedy jog. The jog then quickly turned into actual running, and the 48-year-old mother of two was soon shedding pounds to become a bigger loser than the folks she loved to watch on TV.

“I just walked for months — a lot of months. I just walked and started going to the gym and exercising, working out with weights,” she said. “Then I started walking a little faster and then I started running. I really enjoyed running.”

She enjoyed running so much, in fact, that she felt it was time to give an actual race a shot. After signing up for and competing in the Over the River Run in Vicksburg, Burkhalter fell in love with the adrenaline-packed atmosphere that race day provides.

“I started out walking races, not running races, and just progressed. Once I started running, I just kept running farther and I did longer races,” she said. “Then I decided I was going to do a half-marathon and got a little ahead of myself and ended up with a stress fracture.”

The injury might have temporarily set her back from her daily workout routine, but it permanently spawned her newest and most enormous goal to date — to complete an Ironman Triathlon. She’ll try this weekend at the Ironman Chattanooga in Chattanooga, Tenn.

“When you’ve got a new routine and you are doing something every day, and all of a sudden you can’t and you’ve lost all this weight, you have to do something,” Burkhalter said. “You’re thinking, what am I going to do? Oh my gosh. What am I going to do now?”

Swimming didn’t hurt her, so she jumped in a pool for the first time in 35 years. Riding a bike wasn’t bad either, so she hopped on one and pedaled around town. She did this while nursing her injury before realizing she could marry the three into the ultimate physical challenge, one that involves a 2.4-mile swim, 112-mile bike ride and a 26.2-mile run: the Ironman Triathlon. It’s widely considered one of the most physically grueling athletic events known to man, and Burkhalter, who once struggled to walk around the block, is now fit for the challenge.

She has spent many a painful month dutifully training for the race, which involves hours of biking, swimming and running over the steep Vicksburg hills.

“You start out with a training plan that starts you at about 10 hours a week,” she said. “You’re going to have three swims, usually three bikes and four runs a week. Then you do strength training a couple of times a week too. Then it gradually progresses you through. As the weeks go on, you build through that.”

Burkhalter will compete in the Ironman Chattanooga on Sunday as a host of family and friends roots her on — including her husband, Fred Burkhalter, who acts as cheerleader, timekeeper and motivator.

“When I finished my first triathlon, my husband said ‘How are you doing?’ I said ‘I’m dying.’ A little bit later he checks my scores and everything and he said, ‘Just wanted you to know, you got beat by a 72-year-old man,’” Burkhalter said, laughing. “He takes great pride in that. He loves reminding me that I got beat by a 72-year-old man. I said I don’t care, he must be a heck of a man.”

But as she prepares for what will be her most difficult competition yet, Burkhalter finds solace in that 72-year-old man. She doesn’t want to be put in a nursing home when she’s that age, either, she said. She wants to be running around one.

“That’s what I want to be doing. When I’m 72, I want to be doing it. I want to still be going. I don’t want to be picking out my assisted living center. I want to still be going.”