Chest muscle injury: minor or major problem?

Musculoskeletal shoulder pain affecting the chest and/or frontal shoulder can be caused by a variety of conditions. These include contusion (internal swelling) from a direct impact, costochondritis (inflammation of the connective tissue between the breastbone and ribs), a muscle sprain and/or tendon rupture of the main pectoral (chest) muscle, and biomechanical abnormalities affecting the shoulder girdle. However, while rare in athletes, another possible cause is as a result of an ‘isolated pectoral minor’ (PMi) tear.

Sports injury research shows that a PMi tear on its own is most likely to occur in sports where there is a likelihood of direct trauma resulting from a blow to the area. Such sports include American football^(1,2) and ice hockey⁽³⁾. However, not all isolated PMi injuries are caused by trauma. For example, one 2019 study reported the occurrence of a PMi tear in a healthy 24-year old woman as a result of performing a ‘side plank’ (core stability) exercise at the gym– most likely occurring due to a loss of endurance during the exercise⁽⁴⁾.

Understanding pectoralis minor function

Before we discuss PMi diagnosis and treatment, it’s helpful to understand a little about the anatomy of the PMi muscle. The PMi is a fan-shaped muscle originating from the third, fourth and fifth ribs and inserting onto the coracoid process (a hooked-shaped projection to which many ligaments are attached) of the scapula, more commonly known as the shoulder blade. Figure 1 shows the overall location of PMi, although not where it attaches on the coracoids process). Importantly, the pectoralis minor is located underneath the pectoralis major (the main chest muscle), which is why it is less vulnerable to injury (being protected by its big brother above!).

In terms of its biomechanical function, the PMi muscle pulls the scapula forward, and downward. Therefore, it is principally used in shoulder movements of depression and abduction – ie movements where the shoulders move downwards and inwards to towards the center line of the chest. In addition, the location and function of PMi means that it can aid somewhat in the process of inhalation as an ‘accessory muscle’ (technically, any muscle attached to the upper limb and the rib cage can act as an accessory muscle of inspiration)⁽⁵⁾.

Figure 1: Anatomy of pectoralis minor (showing relationship with pec major)