I believe that serving with ISR is never forced and could cause injury if practiced incorrectly. Here are some known issues. With forceful and rapid ISR the small external shoulder rotator cuff muscles have to be conditioned to keep the ball of the humerus in place and to stop the arm rotation in the follow through. See recommended shoulder conditioning exercises. Easy, light exercises.
There are also the important safety issues related to technique such as the shoulder high orientation for the serve to minimize impingement risk. Just one very bad motion can cause injury.
1) Jim McLennan short video on the rotator cuff, impingement and serving
2) Todd Ellenbecker video on shoulder anatomy, impingement, and serving. At about minute 8 he describes the same issue as McLennan but in more detail.
If you are concerned because you are having pain, how can you determine that the technique that you use is OK? You have to study and know the proper technique and verify that you are doing it with high speed video or find a well qualified instructor. Keep in mind that the more rapid motions during the serve cannot be seen by eye or even 60 fps video so an instructor who uses HSV is a plus.