Measured Against Reality

Wednesday, August 30, 2006

Sex in an MRI Machine

Sooner or later, people will have sex in or on everything.

That’s just one conclusion we can draw from a study done to see how sexual organs are arranged during intercourse. The researchers recruited people to have sex in an MRI while they snapped some images of what was going on. Large magnets, small spaces, lab coats? Sounds romantic.

Continue reading...The study revealed a few things, one of which is that having sex in a 50-cm diameter MRI tube is not easy, especially for men, and considering that the participants had to keep still while the image was being taken. However, it’s apparently considerably easier if you’re an amateur street acrobat:

We did not foresee that the men would have more problems with sexual performance (maintaining their erection) than the women in the scanner. All the women had a complete sexual response, but they described their orgasm as superficial. Only the first couple was able to perform coitus adequately without sildenafil [Viagra] (experiments 1 and 2). The reason might be that they were the only participants in the real sense: involved in the research right from the beginning because of their scientific curiosity, knowledge of the body, and artistic commitment. And as amateur street acrobats they are trained and used to performing under stress.

Anyway, what they found out is not too surprising. You can see the results below. In case you’re a bit disoriented, you’re looking at the pelvic area of the participants, with the woman on the left and the man on the right.

Midsagittal image of the anatomy of sexual intercourse (experiment 12). P=penis, Ur=urethra, Pe=perineum, U=uterus, S=symphysis, B=bladder, I=intestine, L5=lumbar 5, Sc=scrotum

The only real thing that’s remarkable is how much the penis bends, as much as 120 degrees. This is independent of how far it penetrated, so it’s almost certainly a result of the “missionary position”. Previous studies concluded that the penis would be either straight or in an S-shape, which is clearly not the case. The only other notable thing is how little anything else changes.

Another aspect of sex studied was what happens inside a woman during and after orgasm. Things do shuffled around quite a bit, with the vaginal wall constricting, causing the uterus to rise, and the bladder getting quite a bit bigger:

Midsagittal images of sexual response in a multiparous woman (experiment 9): (left) at rest; (centre) pre-orgasmic phase; (right) 20 minutes after orgasm

All in all, this study isn’t going to revolutionize anything. But it was probably fun to do and we learned something as a result, and that’s what really counts.


  • Schultz, WW et al. “Magnetic resonance imaging of male and female genitals during coitus and female sexual arousal.” BMJ 319 (1999): 1596-1600.

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