Final answer:
The most common head of the pec major to tear is not specified, but injuries to the pectoralis major often occur during forceful motions, such as heavy weightlifting. The provided information focuses more on rotator cuff injuries, which can result from overhead movements or impacts to the shoulder.
Step-by-step explanation:
The most common head of the pec major to tear is not specified in the provided information, which instead focuses on injuries to the shoulder joint and rotator cuff. However, the pectoralis major has two heads: the clavicular (upper) and the sternal (lower) heads. Injuries to the pectoralis major, including tears, can occur due to sudden, forceful impacts or overuse, especially in activities that involve pressing movements or the arm being forcibly extended. An example of this kind of injury might occur during weightlifting, particularly during bench press motions. A hard blow to the shoulder or a fall onto an outstretched hand might lead to various injuries including a tear of the shoulder's rotator cuff or glenoid labrum damage.