Growing up with Jack LaLanne as your dad could be hazardous to your health, ironically. “He was always joking around, showing his muscles, and he’d go, ‘Why don’t you hit me in the stomach as hard as you can?'” the fitness expert’s son Dan Doyle recalls to Closer Weekly in the magazine’s latest issue, on newsstands now. “I’d take my fist, wind up, and my hand would just bounce off his stomach. My hand hurt more than his stomach did. He probably didn’t even feel it!”

Clearly, Jack — who hosted his own daily exercise TV show from 1951 to 1985 — “wasn’t your typical Leave It to Beaver type of father,” Dan says. Agrees sister Yvonne LaLanne, “It was unusual having a father of that build. You don’t often have fathers who walk on their hands at birthday parties.”

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Jack was a true believer when it came to physical fitness. “I do it as a therapy — I do it as something to keep me alive,” he explained. “We all need a little discipline. Exercise is my discipline.” But he wasn’t raised with it. As the son of French immigrants in San Francisco, he was a 98-pound weakling and self-described “sugarholic” who sometimes flew into rages. “At one point, he actually attacked his brother with an ax,” Dan reveals.

That all changed when Jack was a teenager and a neighbor recommended he attend a lecture by health guru Paul Bragg. “He got an earful and turned his life around,” says Dan. “He started changing all his habits.”

In 1936, 22-year-old Jack opened the country’s first health club, in Oakland, California. When the new medium of television came along, Jack saw an opportunity to spread the gospel of exercise and proper nutrition. “He had a gift for selling and presenting information,” says Yvonne. “He did it in the service of good health.”

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Jack became famous for stunts demonstrating his seemingly superhuman strength. He was wed twice, to Irma Navarre (Yvonne’s mom) from 1942 to 1948 and Elaine Doyle (Dan’s mom) from 1959 until his death at 96 in 2011. Together, Jack and Elaine had a son, Jon, and as parents, they were strict — up to a point. “I had a rule as a child that I got two sweets a week,” says Yvonne, who didn’t taste Coke until she was a teenager. Confesses Dan, “He didn’t like it being flaunted in his face, but he kind of looked the other way if you wanted to have a little McDonald’s.”

Yet Jack remained committed to healthy habits until the end. “He worked out the day he died,” says Dan. ‘He was in bed, and he knew it was getting close. He goes, ‘Danny, get me a weight.’ I handed one to him, and he had it in his hand when he passed away.”

The lessons Jack taught will endure forever. “He started a movement that’s unstoppable now,” says Dan. “He changed people’s minds and the way they live.”

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