I have noticed almost a constant pain in my back muscles when I attempt to play max-spin forehand topspin, in the region somewhere between shoulder blades, towards left shoulder blade (I am a right-handed player). The pain is located somewhere around rhomboid major muscle as per this picture (except it's on the left side):
Further thoughts: I feel like when I'm nervous, I'm very strained, the explanation for that is: if my back muscles are strained, I can touch the ball more precisely, which my brain thinks is required to play a very spinny topspin, and then when I go for the topspin, I either miss the ball with the racket (due to strain and attempt for risky fast light touch), or if the stroke is good, I feel certain amount of pain near left shoulder blade. Perhaps when I go for the ball already strained, the topspin motion rips through the back muscles and damages them. It can also be the contrary: sometimes I don't strain the back muscles, and when I go for a risky max-spin ball, the inertia of the hand has to be stopped with the back muscles, and the moment when I need strain the back muscles to bring the torso and the hand back overstrains and damages the back muscles.
My questions are: do you strain the back muscles before hitting the ball? Do you strain the back muscles after hitting the ball (e.g. to bring the hand back)? Have you experienced similar problems, and if so, what is your experience?