What muscles are activated in the back rowing preps 2 when performing with open elbows?

In back rowing preps 2 with open elbows, the activation of the posterior deltoids and deltoids is essential for maintaining the arms at a constant height. This position requires stability and control, which is primarily provided by these muscle groups. The posterior deltoids are particularly engaged to ensure proper shoulder mechanics and to facilitate the movement without compromising form. This setup allows for effective engagement of the upper back muscles while also supporting the shoulder girdle, which is critical during any rowing motion.

Other muscle groups listed in the remaining choices do not play a significant role in this specific exercise. The latissimus dorsi, teres major, and pectoralis major, while important for other pulling or rowing movements, are not primarily active in this particular setup. Similarly, the muscles associated with arm flexion and extension, such as the triceps and biceps, and the lower body muscles listed are not targeted in back rowing preps 2 when the focus is on upper body stability and control. Therefore, the most relevant muscle activation during this exercise is accurately represented by the activation of the posterior deltoids and deltoids to stabilize the arms.