CONTRARY TO their men-of-steel image, all Navy SEALs have to learn how to sew—wouldn't want to be stuck behind enemy lines with torn gear. They also have to find ways to stay in shape in remote places where no gyms exist. So Randy Hetrick, a 13-year SEAL vet, decided to create his own gym, fashioning a suspension training device from a few pieces of webbing and a carabiner. As long as he could find something seven feet off the ground to anchor the system, he could keep in shape anywhere.

The outcome of Hetrick's MacGyvering is the Fitness Anywhere TRX (total-body resistance exercise) Suspension Trainer. The entire unit weighs about two pounds and fits into a stuffsack the size of a lunch bag. While it looks deceptively simple, the TRX is crafted from heavy-duty nylon webbing with built-in handles and an ingenious pair of quick-release strap adjusters to produce a rugged, extremely practical piece of equipment. It attaches to anything from a tree to a hotel-room door (using an optional door anchor) and, with instructions any weekend warrior can grasp, provides a total-body, core-intensive workout. Its adherents range from Saints quarterback Drew Brees to American League MVP Justin Morneau to cycling's greatest sprinter, Robbie McEwen.

I'm no McEwen, but for the past 16 years I've spent three months in the weight room every winter to train as an amateur road racer. When Hetrick first showed me an early version of the system in Santa Monica two years ago, I was skeptical—could this sack of cords really replace a gym's worth of machines? Thirty minutes later, after running through a protocol of single-leg squats, hamstring exercises, and a three-part move called the "atomic push-up," I was convinced it could. And because of the inherently unstable nature of the pendulum-like system, every exercise I performed tested my balance and improved my core strength while working my body as a single chain of strength—just what cycling requires. After my first go on the TRX, I felt soreness in core and stability muscle groups I never even knew I had, a sure sign I was hitting my muscles deep. After using it a few times a week for a month, I was sprinting and climbing hills better than ever before.

Today I take it everywhere, and it's the perfect complement to my on-the-bike training. Instead of meas-uring my effort in reps, I perform exercises on the TRX in timed intervals, for a functional-training workout that stretches, strengthens, and also works both my aerobic and anaerobic energy systems. The accompanying DVDs take you through dozens of positions and moves, and you can put together your own targeted workouts— it's equally effective for climbers, snowboarders, runners, or even golfers. The TRX has also brought my flexibility to a new level: I can mash up yoga with stretches I learned from Fitness Anywhere's Web site, and it's just as good as having an active stretching partner.

Best of all, the whole thing sets up in literally a minute—on the road or out on my patio, where it serves as my personal training center in the space behind my back door. But there's one problem. If I want an excuse to blow off training for a day, I'm out of luck. The TRX is the gym that never closes.

DIY: $150–$200; fitnessanywhere.com