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 ...

When Horton's creation, P90X, hit the fitness industry in 2005, it became a smash hit. The program sold more than 3.5 million copies thanks to its high-intensity blend of circuit-style training ...