Whether it's a light stroll or hitting the treadmill for a four-mile run, people often need motivation to exercise, typically in the form of a peppy or aggressive personality. And with hit shows like "The Biggest Loser" and the immense following of Tony Horton's P90X home fitness program, it's clear that fitness is about star power almost as much as getting healthy.

 

From yesterday to today, let's take a look at the fitness gurus who have inspired people to shape up.

Tony Horton (photos), 52, is one of the hottest exercise gurus with his workout program P90X. The program has been a financial success for Horton, too. Before he hit fame, he served as a spokesman for this 1990s trendy exercise piece (watch the commercial).

Widely known for her appearance on a popular TV weight-loss competition, Jillian Michaels (photos) recently launched her own show (watch clips), in which she encourages overweight families to change their eating and exercise habits.

Jack LaLanne (photos) may have been the original fitness guru, and he's got the nickname to prove it. His exercise TV show was one of the longest-running of its kind.

 

He gained fame for his success as this and wowed audiences with his feats of strength. A proponent of vegetarianism and organic foods, LaLanne has been the face of vitamin supplements and later went on to market these.

Eccentric fitness personality Richard Simmons (what's his real name?) gave America one of the classic workout routines, "Sweatin' to the Oldies." After living most of his adolescence in obesity, Simmons (photos) opened a gym in Los Angeles that helped launch his long career.

 

What staggering statistic did he announce on a recent TV appearance?

Already a movie star, Jane Fonda (who is her famous father?) became a fitness legend in the 1980s and 1990s with a series of aerobics videos that are credited with starting the fitness craze among this group of people.

 

After announcing her retirement from film in 1991, Fonda (photos) made a comeback in this 2005 Jennifer Lopez film.

Despite being born with a physical disability, Billy Blanks (photos) famously invented this type of exercise, derived from martial arts. It attracted millions of followers, including this former "American Idol" judge.

Yes, he played this comic-book character on TV, but Lou Ferrigno (photos) was also a fitness trainer and bodybuilder. In a 1975 documentary, Ferrigno famously tried to beat a bodybuilder-turned-governor at the Mr. Olympia competition.

Fitness and nutritional guru Bob Greene (photos) lucked out to get one of the most famous women in the world as his client. He's the creator of this diet.

"Three's Company" star Suzanne Somers (photos) became synonymous with one of the most iconic piece of 1980s exercise equipment. Who can forget the commercials?

Judi Sheppard Missett (photos) turned her passion for dance into a worldwide exercise phenomenon. Founded in 1969, it's still popular today.

Tamilee Webb (photos) developed a famous series of workout videos in the late 1980s and 1990s that launched her as a bona fide fitness queen and reportedly earned her this much in sales.

Jackie Warner (photos) is the star of this Bravo reality show, where she works to inspire drastic lifestyle changes for overweight clients who are struggling to get healthy. The fitness fiend also has launched another show that features her signature boot-camp-style workouts.

Mari Winsor (photos), a dancer, author and Pilates instructor, is known for her signature low-intensity workouts.

Harvey Walden (photos), a United States Marine drill instructor, is whipping soft celebrities into shape on this reality show.