Final answer:
Internal impingement in the shoulder generally occurs during the late cocking phase of the throwing cycle when the arm is in maximum external rotation and abduction, leading to potential shoulder injuries.
Step-by-step explanation:
Internal impingement typically occurs during the late cocking phase of the throwing cycle. This is when the arm is in maximum external rotation and abduction. At this point the structures at the back of the shoulder are compressed, which can include the rotator cuff tendons and the glenoid labrum.
Because of the repetitive nature of throwing, swimmers' strokes or racquet sports these actions can lead to injuries such as the inflammatory responses and degeneration of the rotator cuff or tears in the glenoid labrum. Moreover this repeated stress increases the risk of a frozen shoulder where scar tissue limits shoulder mobility significantly.