When pulling open a door, which of the following is NOTtrue?  the posterior deltoid shortens   the anterior deltoid contracts eccentrically at the shoulder joint   the motion is primarily in the sagittal plane   the biceps brachii works as an agonist at the elbow joint   the long head of the triceps brachii helps to extend the shoulder joint

The statement that is NOT true when pulling open a door is: "the anterior deltoid contracts eccentrically at the shoulder joint."

Here's why:

1. The posterior deltoid shortens: This is true. When you pull a door open, your arm moves backward. This backward movement, or extension, of the arm at the shoulder is primarily facilitated by the posterior deltoid muscle, which shortens (or contracts) to produce this movement.

2. The anterior deltoid contracts eccentrically at the shoulder joint: This is NOT true. The anterior deltoid is responsible for shoulder flexion, or moving the arm forward, not backward. Therefore, it would not be contracting when you're pulling a door open.

3. The motion is primarily in the sagittal plane: This is true. Movements in the sagittal plane divide the body into left and right halves. Pulling a door open involves moving your arm backward (extension), which is a movement in the sagittal plane.

4. The biceps brachii works as an agonist at the elbow joint: This is true. The biceps brachii is the primary muscle responsible for elbow flexion, or bending the elbow. When you pull a door open, you typically bend your elbow, so the biceps brachii would be working as an agonist, or primary mover, at the elbow joint.

5. The long head of the triceps brachii helps to extend the shoulder joint: This is true