Step 1: Begin with the TRX straps in the lowest point, a few inches above the ground. Place your feet in the straps so the tops of your feet are facing down. Face away from the anchor point.
Step 2: Place yourself into a strong plank position, keeping your feet in the straps. moving further away from the anchor point makes the exercise more challenging.
Step 3: While holding the strong plank position, bring your knees to your chest, then return to the starting plank position.
Step 4: Repeat this movement several times.
How to progress the exercise
As with the TRX Y-Fly, Being that your arms are being outstretched during this exercise, any slight change in angle will create sufficient change in overload to the muscles, so the best progression for this movement is to lower yourself by several degrees towards the floor. Lower yourself slightly more as needed.
As with the TRX Y-Fly, be mindful of your exercise form, as it is easy to compensate with the bigger lat muscles, or by thrusting your hips forward for momentum.