I was whipped frequently as a child, and it caused sensations which I really didn't understand at the time, but I can identify them now.
You see, after a few blows I would feel like I needed to urinate. I would hold it as strong as I could, because I knew that I would get half-killed if I were to wet the bed during a whipping. But the odd part was, after the whipping was over and I could go to the bathroom, I usually didn't need to go after all. I think that my genitals became stimulated by blood flowing to the area being whipped (my buttocks). I mistook this stimulation as a need to urinate.
Of course a whipping isn't direct stimulation, but if the genitals end up being stimulated - it's the same result. I imagine that for some children a paddle would have the same result.
I have never been able to relax and enjoy sex with my fiance, When we are intimate, it's okay and feels good at first, but then all of a sudden it seems like I can't feel anything anymore - this always happens WAY before orgasm, usually even before we begin actual intercourse. It is quite frustrating, as I'm sure you can imagine. A therapist told me, "the body remembers what the mind forgets." I think this is true in my case - I think in the initial stage of arousal, my body anticipates pain and so I am unable to feel pleasure. In case you think this therapist gave gave me this idea, I can assure you that I already thought that to be the case before I went to see her. It just seemed like she expressed it well.
I love my fiance very much - it is very distressing that an act which should bring us both pleasure usually doesn't.
I am sorry if some people think this is too graphic to describe in this forum. This is very difficult for me to write about, but I think parents should be aware of the possible long-term effects of their discipline. This is not a theory - it is my personal experience.