With the straps at mid-calf length, place your feet into each of the foot cradles.
Lift your knees off the ground, coming into a plank position with your hands directly underneath your shoulders. Your back should be flat, and your core should be engaged (there should be no arch or dip of the torso visible).
Bring your left knee to your left elbow, then return to your starting position. Bring the right knee to your right elbow. This completes one rep. As you become familiar with the movement, begin to pick up the pace.
Be sure to avoid sawing the TRX (the handles move up and down) by putting even weight into the foot cradles.
Repeat for a total of 12 reps, then rest for 45 seconds.