In order to describe the physical aspects of female orgasm in a meaningful way, I'll first explain to you a few of the physical changes that start well before a vaginal orgasm.
When a woman becomes sexually aroused, her heart beats faster and she breathes more quickly. Often, she'll tighten various muscles all over her body. Breasts usually enlarge somewhat and nipples tend to stand out. Some women flush red on their face, neck, and chest. The visible part of the clitoris also swells slightly.
At the vagina, secretions occur inside and at the opening. Her labia flatten out and open up somewhat. The vagina lengthens and widens internally, changing what was a potential space into more of an actual space. These vaginal changes are mainly due to a rush of blood to the pelvic area -- called engorgement -- that provides a generally pleasurable warmth in a female's genital area.
As her arousal climbs, engorgement increases and most of the changes mentioned above become more pronounced. The one area that doesn't follow the pattern is the clitoris. Instead of swelling more, it retracts under the clitoral hood and decreases in length by about 50%. That's a good sign, though -- orgasm is not far away for most women if optimal stimulation continues.
Now to the climax of our story: Orgasm itself begins with strong muscle contractions that are felt primarily in the outer third of the vagina (the part of the internal space that's closest to the outside of the body). The contractions can be over within four seconds or last up to about 15 seconds. They tend to occur at intervals of 0.8 seconds. Also, the inner two-thirds of the vagina usually open up even more and the uterus contracts as well.
During orgasm, skin flushing generally reaches its maximum. Muscles may keep contracting, and blood pressure, heart rate, and respiratory rate go higher still. Some people make sounds reflecting the pleasure they are experiencing. Subjective reports frequently mention a sensation of tingling in the spine, brain, and genital areas. Some women have an experience that feels like passing out; others report enjoyment but something less than "the earth moved."
