Exploring the pectoralis major muscle
Pectoralis major is one of the muscles that move the humerus at the shoulder joint. It’s a broad, powerful muscle and it’s the larger of the two pectoralis muscles. Everyone is familiar with bodybuilders squeezing their arms in front of their body to show off their big “pecs”! And, that’s the very same pectoralis major muscle we’re talking about here.
When beginners are doing a posture such as chaturanga dandasana, but can’t keep their elbows in, this muscle is likely contracting. In that situation, they’re likely moving their elbows out unconsciously to take advantage of this larger muscle in its action of horizontal abduction. Below we’ll show you some other yoga postures related to this muscle.
What does pectoralis major mean?
The name pectoralis major describes the general location of this muscle. Pectoralis comes from the Latin word “pectus” meaning breast and major comes from Latin and means “greater than.”
Where does the pectoralis major attach?
There are two divisions of pec major. One is called the sternal and the other is the clavicular division.
The clavicular portion originates on the medial (inner) half of the clavicle (collar bone). And, the sternal portion originates on the sternum and the upper 6 ribs.
The two divisions of pectoralis major come together to insert on the lateral (outside) lip of the bicipital groove. Remember that the bicipital groove is the groove at the top of the humerus that the biceps tendon passes through.
What actions does the pectoralis major do?
Consider that the fiber direction from origin to insertion is important in understanding how this muscle creates its actions. The origin of pectoralis is broad and its insertion is small. So, this means that pec major can create opposite actions depending on the circumstances.
It can create a number of actions including:
- medial rotation
- horizontal flexion
Additionally, the pectoralis major assists in adduction. And interestingly, the lower fibers can create extension from a flexed position if there is resistance to movement. Perhaps surprisingly, because of this last muscle movement, the pectoralis major could be seen to be an antagonist to itself.