Step 1: Assume a split stance, facing 90 degrees away from the TRX anchor., with your front leg being on the side facing the anchor.
Step 2: Hold the TRX straps at chest level, arms extended. The TRX straps line up with the anchor point, where it forms a line 90 degrees with your extended arm (ie: a backward L).
Step 3: Holding the TRX handles facing your chest, begin to lean sideways, about 45 degrees, away from the anchor, keeping your arms extended and held t chest level.
Step 4: Keeping a stable position, begin to bring the TRX handles towards your chest, then away from you, all the while holding a solid position without moving any other body part.
Step 5: Repeat this movement several times, then repeat on the other side.
How to progress the exercise
The closer your feet are to the anchor point, the more horizontal your body will be to the floor, and the more difficult the exercise will be. If you are further from the anchor point, you will be more upright, which will make the exercise easier.
Performing this exercise with your feet in the TRX cradles/handles, rather than in your hands, transfers the load into your core, which will be greatly needed for spine stability. Keeping your hands in the cradles requires much more shoulder girdle stability in order to perform the exercise effectively and safely.