I thought I'd post this - a quick synopsis of my readings on the mechanics of an erection. My interest in this topic stems, I guess, from my occasional issues with ED (lets face it, most of us don't worry about how our car works till it stops doing so). I read the traditional explanation of how the erection mechanism works - that chemical messaging is involved in causing a dilation of arteries feeding into the penis and that there is a reduction of the outflow by constriction of the veins. At the time I had my doubts that this was the complete story. My experience of the tug-of-war one gets when wearing a chastity device - the would-be erection pushing outwards and the trapped testicles trying to hold it all back seemed to involve a lot more force than one would expect from 120mmHg blood-pressure and a 50mm bore tube - calculating Pi* Sqr(R)*h*Ro*g in your head at the dead of night is one way to suppress a caged nocturnal stiffy. And that impression turns out to be right - research has shown that the pressure inside a human penis can be about 4 times the systolic blood pressure (in animals it can run to several atmospheres pressure!)
The next bit of information that dropped into my musings was that research has shown pelvic floor exercises for men can improve erectile performance by the same amount as Viagra - a message that I think anyone interested in the well-being of a penis, be it as owner or recipient, should be aware of. Further investigation revealed that there is an interesting reflex involving two muscles, the ischiocavernosus muscle and the bulbocavernosus muscle, and sudden pressure changes in the penis. Basically if you squeeze the penis the pressure change triggers these two muscles into action with slightly different delays and durations. It all sounds like a pumping action at work and indeed this mechanism does seem to pump the pressure in the penis up to the elevated figures that have been found.
Next time you have a penis handy give it a try - give it a quick squeeze and note the involuntary twitch that results. So remember ladies, when it comes to a penis, it may like a stroke but it will find a squeeze, quite literally, irresistible 8-)=
BTW - there would appear to be a similar reflex in women (yes, the same two muscles exist in both sexes) and that the blood-flow to the clitoris is enhanced by their twitching. So it seems that during sex we are actually pumping each other up!