Anal Sex question

[justplaying]

A few weeks ago, there was a post about butt plug training. My KH isn't into anal at all, so it's been a long time since I had the pleasure of it. However, that post got me to thinking about something I recall from my college days. I had a girlfriend who was very open to just about any type of sexual experience. One day I suggested anal intercourse and she agreed providing she got to do the same to me. I laughed and said sure, thinking that she wasn't serious. We were both playing around with bondage at the time as well. I like ropes. She liked ropes. Nothing serious, but lots of fun.

Anyway to make a long story short. One day she tied me up such that the soles of my feet were touching and bound tight, with a long thin dildo inserted between them and sticking back towards my anus. I was lying on my back, and next she tied my wrists to my ankles such that the dildo (and my feet) were pulled towards my ass with the dildo penetrating 3 maybe 4 inches deep. Bound like that I couldn't touch her or myself, so she teased me unmercifully, but would not let me cum. AND now here's the kicker and my question....

When I moved my knees towards each other (raising them up from my sides, but keeping my feet flat on the bed) my legs would shake in violent spasms. I shook so hard my hips were vibrating. She would have me lift and then lower my knees and each time I hit a certain spot, my legs would spasm. It felt amazing and when she finally let me orgasm with the spasms going full tilt I nearly passed out from the rush.

So here's my question: What causes this uncontrollable twitching /spasm to occur? Did anybody else ever have that happen to them? I know some of you have medical backgrounds so maybe you could explain what triggers this reaction. Thanks in advance, Justplaying

[Harry Haversackers]

I have no idea what the underlying physiology is, but I get the same thing when playing with my Aneros prostate massager, while on my back with my knees raised. It starts with my legs shaking and gradually becomes more and more violent until I'm bouncing around on the bed. It's not an unpleasant thing, just kinda weird.

[justplaying]

Harry, That's it exactly! I agree it is not unpleasant. However, I noticed that It only seems to happen when my knees are lifted to a certain point. The shaking can go on for quite a bit and when combined with tease and denial it is amazingly pleasant. I suspect that it is tied to the PC muscle group, but what triggers it? Pressure on the prostate? I have read about the Aneros prostate massage, but never used one. If this reaction is part of the deal, they should advertise that point. I would think more men would want to try their product if they knew it could create this type of pleasure. Does this sort of thing happen in women? I never did get to reciprocate tying her up to find out and then we broke up. I may never know the answer. Thanks for your reply. At least I know it's not just me now...

[Harry Haversackers]

justplaying, Apparently, this is not the desired reaction for those really into the Aneros thing. They're after supposedly incredible dry orgasms with no refractory downtime (which doesn't sound like a bad thing, does it?). I mentioned that I don't find it unpleasant, however, after a while, it's really tiring, because it can get so damned vigourous.