"Power lives in the transverse plane" is a famous line by many popular movement-based professionals for a good reason. Most sports, if not every sport requires force generation AND movement control in the transverse plan. For simpler terms, owning rotational movement is key to performance success.
Common popular exercises include the Pallof Press, lateral jumps, diagonal chops, etc. The list goes on forever, but here is solid TRX variation training the upper body in rotation. The Rotatory exercise hits the upper body AND the core. As you can see, my arms are doing a lot of work, but my core is working too to stay in sync with my upper body. This a killer workout for the chest, the shoulders and arms, and the obliques. A lot of the back rotatory muscles are working hard here too.
Don't forget, the TRX and other similar suspension trainers demand stability from head to toe. During this exercise it is important to keep optimal alignment.
1) Maintain an erect torso with the legs straight
2) Try to keep the head, neck, arms, and torso aligned
3) Try to keep your arms straight as much as possible, but as your feet get closer to the anchor, it will be more challenging.
4) Always remember to breathe and keep a solid tempo, quality > quantity