The twin pectoral muscles, pectoralis major and pectoralis minor, are primarily used to control movement of the arms, explains Healthline. In addition, they assist deep breathing by stretching the rib cage, thus increasing its volume. Pectoral muscles are colloquially referred to as "pecs," notes Wikipedia.
The pectoralis major muscle is reminiscent of a fan, notes Healthline. The wider end of the muscle is attached to the breastbone while the narrower end converges at the shoulder. The thinner pectoralis minor muscle lies under the pectoralis major. While visible in men, pectoral muscles are hidden by breast tissue in women. Pectoral muscles keep arms attached to the rest of the body, explains Wikipedia. Without these muscles, throwing balls, skipping ropes, lifting weights and flapping arms would be impossible.
Pectoral muscles can tear, impairing their function, warns Healthline. This is particularly common during weightlifting and other activities that place excessive strain on the two muscle groups. Tears tend to be more frequent in men, explains Wikipedia. This is because men have a lower tendon-to-muscle ratio, tend to exercise more energetically and have less flexible muscles.
Pectoral muscles can also develop tumors, a problem typically solved through surgery, notes Wikipedia. A far less common problem affecting pectoral muscles is Poland's Syndrome. This refers to the absence of the two muscle groups on one side of the body. The condition is almost always congenital.