Final answer:
The deltoid muscle in the shoulder performs several movements like abduction, flexion, and medial rotation of the arm. However, when gravity is a factor, shoulder flexion is minimized. This means that raising the arm becomes more difficult due to the counteracting force of gravity.
Step-by-step explanation:
The shoulder joint is made up of several muscles that allow movement in multiple directions. The deltoid muscle, located on the shoulder, is responsible for various movements including abduction, flexion, and medial rotation of the arm. However, when considering the influence of gravity, shoulder flexion (movement that decreases the angle of the joint) is minimized. This means that when the arm is flexed at the shoulder, gravity counteracts the movement, making it more difficult to raise the arm.