Final answer:
The upright row exercise primarily targets the trapezius and deltoid muscle groups, with the erector spinae providing supportive stabilization.
Step-by-step explanation:
The upright row primarily targets the trapezius and deltoid muscle groups of the upper body. These muscles are responsible for the lifting and rotation of the shoulders, as well as for some of the movement in the upper back. When performing an upright row, the motion involves elevating the shoulder girdle while keeping the hands close to the body, which effectively works these muscle groups. It's important to note, however, that the erector spinae group, while not the primary target of this exercise, does play a supportive role in maintaining proper posture during the movement.