[2][3] The mechanics of sex under limit circumstances, such as sexual activity at zero-gravity in outer space, are also being studied.
[4] Pioneering researchers studied the male and female genitals during coitus (penile-vaginal penetration) with ultrasound technology in 1992[5] and magnetic resonance imaging (MRI) in 1999, mapping the anatomy of the activity and taking images illustrating the fit of male and female genitals.
[6] The magnetic resonance images also showed that the penis has the shape of a boomerang, that one third of its length consists of the root of the penis, and that the vaginal walls wrap snugly around it.
[6][7] Moreover, MRI during coitus indicate that the internal part of the clitoris[8][9] is stimulated by penile-vaginal movements.
[10][5] These studies highlight the role of the clitoris and indicate that what is termed the G-spot may only exist because the highly innervated clitoris is pulled closely to the anterior wall of the vagina when the woman is sexually aroused and during vaginal penetration.