One of the most common motivators of healthy lifestyle changes is a scary medical checkup. But for Juan Carlos Diaz Arelle, 54, it was a little different. Having done numerous triathlons between 1999 and 2011, he was not just scared but shocked when his doctor told him in January 2019 that he was heading in a bad direction.

Married and the father of three sons, Juan Carlos, who works as a banker in Mexico City, did not need any further encouragement to start a comeback. But his body could no longer handle the same training mistakes he used to get away with when he was younger, and he finished his first race—a half marathon—with a torn glute muscle. Then he got another scare, this time in the form of an ultimatum from his wife: If he hurt himself again, he was done.

Wisely, Juan Carlos decided to get some help in pursuing his next goal, which was to finish Ironman 70.3 Campeche in less than six hours. A friend recommended that he read 80/20 Triathlon and follow one of its training plans, so he did. But it was a big adjustment. “Many times in training I would think the pace was easy, I could go faster,” he says, “but my mantra was, ‘Trust the program, keep the pace.’”

He’s glad he did. When he crossed the finish line, Juan Carlos checked his time and got the good kind of shock: 5:31:10—a PR after 11 years away from the sport. “The best thing is that, throughout the training plan, I always felt great,” he says. “I was never injured and enjoyed the experience.” With his wife’s full support, Juan Carlos is now aiming to qualify for the 2021 Ironman 70.3 World Championship.