For a time, he also earned a living as a stand-up comedian; but, following his love of fitness, he began working out at the World Gym in Venice, California, which had been frequented by professional bodybuilders such as Arnold Schwarzenegger and Lou Ferrigno. In an attempt to avoid the bulky, non-flexible bodybuilder look, Horton focused more on exercise routines to bring about speed, flexibility, and balance, as well as muscle growth. Later, he collaborated with former-triathlete and Ironman competitor Mark Sisson, who introduced him to interval training.
It was also during the early 1980s that Horton became a personal trainer and established his business, ASH Fitness (based on the initials of his given name), in Santa Monica. He began to gather a list of clients that boasted such artists as Billy Idol, Tom Petty, Lindsey Buckingham, Stevie Nicks, and Bruce Springsteen. More recently, he has trained multiple-Grammy-winner Usher Raymond and actor Ewan MacGregor, and he has developed workout plans for a variety of health and fitness magazines. Prior to his success with P90X, Horton served as spokesman for NordicTrack exercise machines. Horton is on the Board of Directors of GO Campaign, a nonprofit that supports orphans and vulnerable children around the world.
When Beachbody asked Horton to help develop and star in a workout video series, his biggest early success came in 2001 with Power 90, an in-home boot camp-style program. Power 90 combined quick, intense cardiovascular exercises with moderate-level strength and weight training moves. Power 90 was followed by a variety of other one-off fitness series; and by 2004, Horton had created the much more intense P90X program, which delivers a “ripped” physique to those who follow the rigorous workouts and meal plans for 90-day rounds. P90X features workouts with such participants as Dreya Weber, among many others. Adapting his penchant for bodyweight and resistance training exercises and yoga, Horton compiled in P90X a format that also included cardio training, jump training (or plyometrics), and the martial art of kenpo. The varied workout schedule is based on the concept of “muscle confusion,” a form of periodization or cross-training that is designed to achieve maximum results while avoiding the plateau effect, allowing muscle groups to continuously improve during phases of controlled yet unfamiliar movements. It was due to the concept of muscle confusion that Billy Idol nicknamed Horton “Muscle Confucius”. After the P90X program was released, the P90 Master Series workout was created as a bridge between Power 90 and P90X. P90X has become the best-selling product offered by parent-company Beachbody, with an estimated 3 million copies having been sold, as of November 2010.
In 2007, Horton created P90X+, a series of follow-up DVDs designed as a supplemental series for graduates of P90X, although P90X+ was not a stand-alone series as was P90X. Ten-Minute-Trainer, a collection of brief workouts designed for those with tight schedules, came to the fitness market in 2008. Also in 2008, “Tony Horton’s One-on-One” series, a monthly offering of individual workouts, has continued to provide high-intensity workouts in a minimalist style, as they feature Horton personally engaging in extreme exercise routines filmed in his home fitness studio by Mason Bendewald. The series was renamed “P90X One-on-One” and aimed as a trial program for the upcoming P90X:MC2. Rodale published Horton’s first book, “Bring It!”, in December of 2010.