That can hurt!
Did you know human skin and tissue can tolerate only 1.23 to 1.5 lbs of pressure per square inch before being damaged? Studies show horses can tolerate about the same pressure. Note how a horse's skin will flick when even a fly lands on it. An average general-purpose saddle has a contact surface of about 96 square inches. A 150 lb. rider has a concussion factor of double that or 300 lbs. 300/96 produces a pressure factor of just over 3 lbs/sq. inch - well over that which is recommended.
I want to tell you a story about a Paso Fino, whose owner called me one day. She told me that her horse was a wonderful loveable even-tempered horse that she had sent away to be trained.
The horse came back very ill tempered. So, ill tempered that the people who owned the barn that she was at, told her the horse was dangerous and should be put down before it hurt her or the staff. I, of course, was very interested to see if I could help the horse.
When we arrived I immediately went to the horse's stall, and sure enough, he laid his ears back and showed me his teeth when I entered. I quickly stepped aside and ran my hand along his back very softly. The horse just about dropped to his knees. I began to do some very light massage, the horse responded very favorably.
I then asked to see the saddle that she was using. She said it was the saddle that the trainer was using. The trainer had sold her the saddle.
Eventually I got on the gelding bareback and rode it with no problems. I encouraged her to burn the saddle, get a good massage therapist, ride him bareback for awhile and look for a proper fitting saddle. We helped her with all of that and within the year he was a totally different horse. Now, this is the extreme. In our saddle fitting clinics we see many horse's that have issues so small that the owners are not even aware of the issues.
Check your saddles and there fit carefully your horse will love you for it.