Which exercise is designed to improve upper body efficiency?

The correct choice focuses on the concept of improving upper body efficiency through a specific exercise. Stationary arms, often incorporating isometric holds or movements that engage stabilizing muscles in the shoulders, chest, and arms without the need for dynamic motion, can enhance muscular endurance and control in the upper body. This exercise can help athletes and individuals develop a stronger foundational coordination and stabilization, which is critical for performing various movements effectively.

When considering the other activities, bench presses, push-ups, and pull-ups are dynamic exercises that primarily focus on strength building in the upper body. While they are effective for increasing muscle size and strength in specific muscle groups, they don't specifically target the concept of "efficiency" in the same manner. Efficiency in this context relates more to the ability of muscles to work together smoothly and effectively during motion, which stationary exercises can help develop more effectively in a controlled manner.