Starting Position: Holding both TRX handles or foot cradles in your left hand, turn yourself to face away from the anchor point. Extend (straighten) your left elbow to chest height, position your wrist in neutral (straight, not bent) with your palm facing the floor. Retract and depress your left scapulae (pull your left shoulder down and back).
Assume a split-stance position with the right foot forward, lunging forward slowly and allowing some bending at the hips until the straps become tight. Maintain this foot position throughout the exercise. Stiffen your torso by contracting your core/abdominal muscles ("bracing"). Gently lower your upper body towards your left hand while keeping the head and spine aligned, and avoiding any sagging in the low back.
Upward Phase: Exhale and slowly extend (straighten) your left elbow by pressing your entire body away from your arm. Your upper arm should remain level with your chest, your body should not rotate and your wrist should remain in the neutral (straight, not bent) position. Maintain a stiff torso aligning your head and spine, and avoid any sagging or arching in your low back or hips.
Downward Phase: While maintaining your rigid torso, inhale and slowly lower your body back towards your starting position keeping your head aligned with your spine. Repeat to the opposite side, changing your arm and leg positions.
Exercise Variation: To increase the intensity of this exercise lengthen the straps and position your body further away from under the anchor point, or change the foot position so that the ipsilateral (same-side) leg is forward.