Originally Posted by idomin
I didn’t find anything how to strengthen the base (since I feel with a strong base the girl can lean back and I won’t have the feeling described above), is it not possible?
You’re kind of missing the point I think. As marinera pointed out, it is a flexibility issue with ligaments when a strong erection is achieved. While connective tissue can be made stronger (although I am not sure how in this case), this will not decrease the pain you are experiencing because the problem has to do with flexibility rather than strength. If you gain flexibility then the base will have an increase in mobility, reducing your pain through your current range of motion. The “pole in the cement” situation cannot be simultaneously achieved while avoiding pain because this tissue is different than a muscle. A muscle flexes against resistance, and can be trained to withstand stronger resistance. Ligaments mostly just become more flexible.
If you find that a particular girl enjoys leaning back to the extent that it causes you serious pain, just be open with her about it. I don’t want to go into graphic detail, but there are plenty of other positions in which you can stimulate that same area, although she may feel a stretch instead of you. It’s just a matter of angles.