Final answer:
Gravity minimizes horizontal abduction of the posterior deltoid muscle in the shoulder.
Step-by-step explanation:
The posterior deltoid is a shoulder muscle that is responsible for horizontal abduction, along with other movements. Gravity plays a role in minimizing the shoulder muscle's horizontal abduction because it acts as a force opposing the movement. When the arm is horizontally abducted against gravity, the posterior deltoid needs to exert more force to overcome gravity and complete the movement.