Would you have believed 300 flabby, overindulged actors could hold off an angry horde of invading Persians? Me either. So the producers of the movie "300" had a choice: whip their cast into fighting shape, or use inexperienced gym rats who looked the part, but couldn't talk and hold a shield at the same time.

With a huge Hollywood budget on the line, they wisely decided having to listen to their actors whine and moan their way through a grueling fitness regimen was easier than trying to teach a bunch of jacked-up meatheads to emote. And the program they chose was CrossFit.

Developed by a former gymnast as a way to create the "quintessential athlete" - equal parts gymnast, weightlifter and sprinter - CrossFit doesn't use fancy equipment, but rather your own body's resistance with exercises such as squats, running, pull ups, sit ups, etc. performed at high intensity. Really high intensity. A typical workout lasts only about 20 minutes, but looks something like this: Three rounds of 21, 15 and 9 repetitions of Dumbbell Bench Press, Weighted Sit Ups, Push Ups, Kettlebell Snatches and Push Presses, back to back, as quickly as you can complete them. And your goal each workout is to beat last session's time.

Over 400 gyms across the country offer CrossFit training classes, with one of them being Petranek Fitness in Santa Monica. (Club motto: "No One Ever Drowned in Their Own Sweat." And I did not make that up.) Owner Andy Petranek (pictured), is a former Marine who has competed in the 300-mile Eco Challenge. Since the equipment necessary to train CrossFit is minimal, you can log on to the gym's website, www.petranekfitness.com, get the Workout of the Day, and do it at home. Videos on the site show you how each exercise and workout are done.

Since you are competing against yourself, guys of any age and fitness level can benefit from a CrossFit workout. Whether you need to fight off a Persian horde, or just want to look like you could.

www.PetranekFitness.com