When part of the body, such as the arm, is moved away from the midline of the body:

This movement is called "abduction". Here are the steps that describe this process:

1. The process begins with the contraction of the muscle responsible for the movement. In the case of the arm, these muscles could include the deltoid, supraspinatus or the serratus anterior.

2. The contraction of the muscle pulls on the tendon, which is attached to the bone of the arm.

3. This pulling force causes the arm to move away from the midline of the body.

4. As the arm moves away from the midline, the angle between the arm and the body increases. This is the main characteristic of abduction.

5. Once the desired position is reached, the muscle contraction is reduced and the arm is held in place.

6. To return the arm back to the body's midline, the opposite muscles (adductors) contract to pull the arm back towards the body. This movement is known as adduction.