Exercises that work the pectoralis muscle have the potential to cause anterior shoulder pain. In fact, the most common cause of shoulder pain after working out with weights is the stress placed on the shoulder by the bench press.

The two most common exercises for the anterior chest muscles are the bench press and the side fly. The straight branch press is the most common exercise. Incline press and declined bench press are also used.

The starting position is with the bar directly in front of the chest. It should be lifted off of a bench press rack. The bar is brought down to the chest and then pushed off of the chest to return to the starting position.

This grip will help build the medial portion of the pectoralis muscle. It will, however, put a tremendous strain on the AC joint and will eventually cause degenerative arthritis of the AC joint and chronic shoulder pain.

Widening the grip on the bench press will decrease the strain on the AC joint. This will reduce the pain that is associated with doing chest exercises. This wider grip will tend to build up the more lateral pectoralis muscle, that is, the part of the muscle toward the arm. This grip also focuses the strain on the pectoralis muscle and isolates the muscle. The lifter is not able to use his triceps (arm muscles) to help with the exercises

Using too wide a grip is not advisable. This increases strain on the arms and does not the exercises to be done efficiently.

Side Fly
In the side flying the arms are brought from the upright position to the lateral position. The elbows are slightly bent. Dumbbells are used for this exercise.

The elbows should be slightly bent to prevent damage to the elbow. The hand should be rotated so that the palm are pointing upward.

The top of the stroke should not allow the dumb bells to touch. The hand and arms should be pass into the danger zone. Doing so will eventually produce shoulder pain and degerationo of the AC joint.

All chest exercises use the same muscles and encorporate the same shoulder motions as the bench press and sidefly.

With new types of exercise equipment the motions of the side fly and the bench press are reproduced by the various machines. The motion, however, is exactly the same. The resistance is exactly the same.

These exercises can further be modified by changing the direction of the resistence. Pushing the weight upward toward the upper chest in a position halfway between the overhead position and the straight bench press position is called an incline press. Pushing downward toward the foot is called a decline press.

Very few injuries occur while working the pectoralis muscle. The only ruptures of the muscle I have seen have been in weightlifters taking anabolic steroids

The combination of incline press straight bench press and the declimb press produce the most effective program to exercise the pectoralis muscles.

The number of repetitions of each pectoralis exercise depend on the goals of the lifter.