Tony Horton, best known for the P90X workout, says he's thriving at 66 after tweaking his routine. Horton was diagnosed with a rare illness in 2017 and has since followed a flexible plant-based diet.

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Two decades after designing one of the best-selling home workout programs in history, the personal trainer Tony Horton says he's in the best shape of his life. When Horton's creation, P90X, hit the ...