Step 1: With the TRX straps set at three inches above the ground, place your feet in the stirrups so the tops of your feet are facing the floor.
Step 2: With your hands placed on the floor at shoulders with, begin this exercise from the plank position (abs and glutes engaged, shoulders stacked above wrists, keeping a straight solid line).
Step 3: Begin the movement by engaging your shoulder girdle stability with your scapulae depressed.
Step 4: Shift your weight slightly forward so your shoulders are in front of your hands; at the same time, proceed to bring your knees towards one shoulder, in an arc motion parallel to the floor, focusing on engaging the abdominals (not the hip flexors). You are still maintaining a strong plank position with your core and glutes tight.
Step 5: Return back to the starting plank position, then bring the knees towards the other shoulder, in an arc motion once again.
Step 6: Repeat this arc motion from shoulder to shoulder several times.
How to progress the exercise
A progression of this already advanced exercise would be to hold the pike position longer. This will put more stress on the shoulders, wrists, and hands, as when holding a handstand. Try placing your hands on a balance disc or BOSU for a shoulder stability/balance challenge!
Strong abdominals are needed for this exercise, to avoid overcompensating with the hip flexors.