Article by Dr Paul Batman, PhD.
The pectoralis major is a multi pennate muscle that is fan shaped in appearance and twists on itself at its insertion. The pectoralis major consists of 2 separate parts, a clavicular and sternal portion. The sternal part twists 180 degrees on its insertion.
Medial half of the clavicle, sternum and first six costal cartilages.
Lateral lip bicipital groove and crest below the greater tubercle.
The pectoralis major is part of the following muscle groups:
Shoulder joint flexors (clavicular), shoulder joint extensors (sternal) only to the anatomical position after which it loses its angle of pull, shoulder joint adductors (sternal), shoulder joint horizontal adductors (both), shoulder joint diagonal adductors (both), shoulder joint medial rotators (both against resistance), shoulder joint abductors (clavicular above the horizontal).
Front arm raise (flexors), narrow arm pullup (extensors), lat pulldown (adductors), bench press (horizontal adductors), t bench medial rotate (medial rotators). More emphasis can be placed on the pectoralis major by keeping the arms straight and isolating the movement at the shoulder joint eg. supine flyes.
CASE STUDY STRENGTH EXERCISE: BENCH PRESS
1. Lie on a bench in a supine position with your eyes directly above the bar
2. Anchor your feet so that they are placed firmly on the floor or raised platform
3. Position your hands equal distance from the centre of the bar, slightly more than shoulder width apart
4. Contract your abdominals to support your lower back
5. Lift the bar off the rack, extending your arms so that the bar is positioned directly above the base of your neck
6. Just before lowering the bar, breathe in
7. From this starting position slowly lower the bar until it touches your chest and hold firmly with your upper arms parallel to the ground
8. Commence the up phase by straightening your elbows and pressing the bar back to the starting position, breathing out as the weight is being lifted.
Double arm chest stretch, single arm chest stretch, leaning shoulder stretch (sliding back on arms).
CASE STUDY STRETCHING EXERCISE: DOUBLE ARM CHEST STRETCH
1. Stand in an upright position with your arms placed to the side of your body at shoulder height
2. Have your thumbs pointing up and the palms of your hand facing forward
3. From this position slowly pull your arms back as far as possible to a comfortable position until you feel the stretch in your chest
4. Try to bring the backs of your hands together while keeping your arms straight
5. Hold the stretch for approximately 20 seconds and then return your arms back to the starting position.
Palpate the pectoralis major by sweeping your hands across your chest from your sternum towards your shoulder. Horizontally adduct against resistance. The clavicular part can be felt below the medial two thirds of the clavicle while the sternal portion is found below the clavicular part.
- When examining the chest of a body builder it becomes obvious that the pectoralis major has a separation between its sternal (lower) and clavicular (upper) parts. They could be regarded as individual muscles, although they have similar movements they do have different nerve innervation. This in turn allows them to be responsible for different movements, even though at times they are called into action together because of their common tendon of insertion. There appears no question that the both parts of the pectoralis major can be exercised separately and should be for maximum benefit. To achieve a maximum contraction of the clavicular part resistance must be encountered. Some trainers have suggested that it is possible to develop the inner and outer portions of the pectoralis major. At present this appears not to be the case, as the same nerve is supplying both the inner and outer parts of the muscle.
- In a seated row (neutral grip) the pectoralis major contracts in shoulder joint extension. When the seated row is performed with a pronated grip the action at the shoulder joint changes to horizontal abduction, eliminating the involvement of the pectoralis major.
- When an overhead press/military press/shoulder press is performed the clavicular part of the pectoralis major is active in the last half of shoulder joint abduction (above the horizontal) reaching its peak at approximately 110 degrees of abduction. This is due now to the angle of pull of the muscle being above the centre the shoulder joint. As the arm is moved forward of the body the action of the shoulder joint changes to flexion, placing more emphasis on the clavicular part of the pectoralis major for a greater range of movement.
- In alternate front arm raises, when the arm is flexed forward of the body the clavicular part of the pectoralis major is active until approximately 115 degrees, slightly above the horizontal.
- In a wide grip lat pulldown the sternal part of the pectoralis major contracts significantly from 90 degrees adduction/abduction of the shoulder joint. In the narrow grip lat pulldown the sternal part will contract from the beginning of the exercise until the arm is located to the side of the body. Beyond this point the pectoralis major ceases to contribute.
- In a decline bench press (angle of decline most efficient at 20-25 degrees) greater emphasis is placed on the sternal part of the pectoralis major, while in the incline bench press (angle of incline is most efficient at 15-30 degrees) the clavicular part makes a greater contribution.
- Maximum isolation of the both parts of the pectoralis major is achieved in a barbell bench press performed with a wide grip and the elbows out to the sides. The movement responsible for the exercise is shoulder joint horizontal adduction, the common action for the both parts of the pectoralis major.
- The pectoralis major works closely with the anterior deltoid. The loss of function of the pectoralis major is less severe than that of the anterior deltoid.
- A postural condition of the upper body that results from a shortened pectoralis major is round shoulders. This sometimes causes excessive medial rotation of the shoulder joint and abduction of the scapula.