As with many great innovations, suspension training was born out of necessity. Randy Hetrick, a Navy SEAL and elite squadron commander, needed a lightweight, easily transportable device capable of keeping him in fighting condition no matter where he happened to be deployed. Since Hetrick often found himself bottled up in a submarine or a safe house, or dispatched without notice to some bare-bones overseas base, conventional strength development proved difficult. Total body training "was hard to do in places where you didn't have access to a pull-up bar and didn't have any weight machinery," says Hetrick.

Luckily, Navy SEALS tend to be resourceful soldiers, adept at equipment modification. After commandeering a spare parachute, an old gear bag and a boat repair kit, Hetrick stitched together some military-grade nylon webbing, fashioned handles and an anchor, and created what would come to be known as the total-body resistance exercise trainer, or TRX. The thing was crude looking and a bit ungainly- Hetrick would spend the next several years fine-tuning the device-but its utility was immediately apparent. Almost by chance, Hetrick had discovered an elegant, gravity-based solution to his workout dilemma. Although he didn't realize it at the time, he also had planted the seeds of a fitness craze.

TRX suspension training is to weight machines what Rocky Balboa was to the Soviets: simple, almost to the point of boredom, yet highly effective. TRX is a system of adjustable straps that allow users to employ their own body weight as resistance. (Imagine the shoulder workout a gymnast gets while performing on a set of rings, and you begin to get the idea.) To increase or decrease your workout level, you change the angle of the straps or the angle of your body. "If you use gravity and angles and a fixed attachment point, you can do literally hundreds of exercises for every muscle group in the body," says Hetrick.

The prototype that Hetrick developed was an immediate success with his squadron. Before long, his men adopted the system and started acting as a sort of viral public relations team, promoting the TRX to their friends. Hetrick quickly recognized the potential of his device. Believing that suspension training could become a successful business, he applied to Stanford, earning an MBA. All the while, he continued to work with the TRX. "I knew I had something when they saw me training in the weight room for the first time and one of the guys came over and said, 'I'll be damned, what is this thing?'"

Hetrick released the TRX in January 2005, relying entirely on word-of- mouth marketing. Despite the soft sell, it caught on immediately: first with the military, then with personal trainers and performance coaches, then with hard-core athletes, like NFL quarterback Drew Brees. "It's just exploded across the world of professional sports," Hetrick says. "It took a little while initially to get people to be able to understand it. We had a hard time even describing it because it was quite a different approach to training than most people have ever done. [But] we seem to be lighting on fire right now." Sales are expected to top 30,000 units this year, and, inevitably, Hollywood celebrities including Bruce Willis and Sylvester Stallone began to crash the party. Professional triathletes such as Jessi Stensland, Marilyn MacDonald and Chris McDonald also are devotees.

Military branches and personnel account for half of all TRX systems sold, but lately professional and collegiate athletic programs have been especially keen on the TRX, recognizing that it offers an ideal total body fitness solution-particularly for athletes recovering from injury, as Brees was when he began using the system. "The great thing about TRX is- because you're using your body and planes of motion unconstrained- the body has to perform the movement using its own weight and generate the stability, just as you would in a sport," says Hetrick. "It ends up being this tool for a whole range of sports because you can design the movement to exactly mimic the analog movement that's particular to that sport or activity."

The TRX is also ridiculously efficient. "You strap it on and in 20 minutes you can get more strength work than most triathletes will get in a week." As such, TRX is becoming increasingly popular in fitness clubs and with trainers throughout the United States, including many in Chicago. Local trainer Dan Chisholm (danchizam@aol.com) stumbled across suspension training at a fitness show three years ago. "It was kind of silly looking," Chisholm says, "but I did one set of exercises and my abs were killing me." He has since become a convert, and-like so many before him-a walking TRX testimonial. "If I was stuck on a desert island," Chisholm says, "this is the one thing that I would bring."

Which, as it happens, is exactly what TRX was designed for. TRX packages start at $145.95. www.fitnessanywhere.com

John Gleason recently moved to Chicago after working as an editor of Mile High Sports magazine in Colorado. He is a former staffer with Men's Health Magazine and consulting writer with the Jimmy Kimmel Live! television show. Gleason loves college football, his mom, press passes and free review products. Reach him at expjournalist@hotmail.com.