Range of Motion ROM

Range of motion is defined as: Joint flexibility is defined as the range of motion (ROM) allowed at a joint. A joint's ROM is usually measured by the number of degrees from the starting position of a segment to its position at the end of its full range of the movement.
In Bodybuilding Range of motion is important for a full muscle contraction and getting the entire muscle involved. A good example of this would be the Pec Deck. You want to open your chest up as much as possible while doing the exercise. By opening the chest you are simply letting the weight of the machine pull your arms back therefore stretching your muscles. As you then pull forward you are engaging all of the muscle tissue from the inside of your pecs (these muscles start the contraction) to the outside of your pecs (these muscles complete the contraction). Range of motion is very important to developing the entire muscle fully. HOWEVER please use lower weights when you are doing full range of motion exercises, the more stretched your muscles are the weaker they are. Picture a rubber band...the more stretched it is the thinner it gets, therefore it is weaker the more it stretched. So if you engage in heavy weights at this point the danger is tearing the muscles you are at max ROM with.

Try this out see how it works. Keep the weights low and feel a good stretch.