Starting Position: Place your feet securely into the foot cradles positioned directly under the anchor point. Flex your ankles and press down with your heels. Gently lie back on a mat/floor with your arms at your sides and palms flat on the ground and legs straight. Engaging your core and your glutes (butt) lift your hips off the floor keeping your body straight and rigid. Use your hands to help stabilize your body. Keep your feet together throughout the exercise.
Upward Phase: Exhale and slowly pull your heels toward your hips. Keep your ankles in flexed, toes toward the ceiling. The hips may bend forward slightly but keep the torso rigid. Avoid any back and forth swinging of the TRX straps.
Downward Phase: Inhale. Slowly straighten both legs to the starting position, with a straight and rigid body alignment. Avoid any back and forth swinging of the TRX straps.
Exercise Variation: The intensity of this exercise can be increased by positioning your body further away from the anchor point of the TRX and lengthening the straps.
Using the TRX certainly enhances the appeal of many exercises; however, trainers and individuals should not participate in these advanced exercises until they can demonstrate capability to effectively stabilize their lumber spine (low back) with their core muscles.