The sternalis muscle is not existent in every human.
Approximately 5% of us have one.
The muscle can trigger pain on the chest and refer it to the shoulder and arm.
If this muscle contains a trigger point, it can cause chest pain and radiating pain into the upper and inner arm.
Hence, it might contribute to your arm pain.
Here you will find the instructions on how to relieve upper arm pain.
Beside the pains described above, which often “feel deep” or have the quality of a sore muscle, the muscle does not impair any movements.
There is no function that can be attributed to this muscle.
As the muscle has no function, there are no activities that are known to overwork the sternalis.
But it is known that it may develop trigger points with acute angina pectoris or myocardial infarction.
Muscles that then might also be affected, are the pectoralis major and the pectoralis minor.
A good way to massage this muscle is using a massage ball against a wall.