When the TRX Suspension Trainer first came out, in 2005, it quickly became a cult hit among gym rats for its deep library of strength exercises and its ultra-portability—allowing you to work out anywhere from a hotel room to a beach with one palm tree ($190; fitnessanywhere.com). But more recently, elite endurance athletes like 2009 Ironman runner-up Chris Lieto have begun turning to the system to supercharge traditional body-weight strength routines. TRX uses a pair of straps hanging from a door or beam to slightly destabilize your body as you run through variations of classic lunges, push-ups, and crunches, fine-tuning the stabilizing muscles your body calls upon late in a race. "The TRX forces you to strengthen muscle as it relates to the movements you'd be doing in your sport," says Matt Dixon, Lieto's coach. "It makes it more real-world." Here's Dixon's four-move core-strength recipe for endurance athletes
Core Strengthening: Sprinter's Start with Knee-up
WHY: "This move strengthens the hip muscles used by runners and cyclists and also engages the core," says Dixon.
HOW: With feet below the TRX anchor point, lean forward with the handles near your shoulders and one foot forward, like a sprinter. Keeping tension on the straps, push forward on your front leg and bring your rear knee through as high as your hips. Repeat.