Final answer:
The effort in the deltoid muscle's lever system is applied near the shoulder joint, which serves as the fulcrum, creating the force needed to move the arm through contractions of the muscle.
Step-by-step explanation:
The deltoid muscle operates in a lever system when controlling the movement of the arm. In this system, the fulcrum is the shoulder joint, and the load could be an object in the hand or the arm's own weight. When the deltoid contracts, it applies the effort needed to move the arm. Specifically, the effort by the deltoid muscle is applied closer to the shoulder, which serves as the pivot point. As a result, when the muscle contracts, the force exerted will vary based on the position of the arm. For instance, if the anterior fascicle of the deltoid muscle is stimulated specificially, it will result in both abduction and flexion of the arm. In simple terms, the effort is applied by contraction of the muscle near the fulcrum (shoulder), which lifts the load at the other end of the lever (the hand or the arm).