What's an Orgasm?

Clinically speaking, an orgasm is just a series of involuntary muscle contractions. But unlike a charley horse, these spasms turn your legs into jelly for an entirely different reason.

It's a great pleasure for some, a frustrating puzzle for others and still much of a mystery to sex researchers, said Debby Herbenick, sexual health educator at The Kinsey Institute and author of "Because It Feels Good" (Rodale, 2009).

During sexual excitement, the heart rate can double, blood rushes to the genitals, muscles tighten, and chemicals and hormones such as oxytocin flood the body. At orgasm, muscles in the pelvis contract, and the body begins to return to a more normal state.

Men and women report similar orgasmic sensations. In one survey, volunteers were asked to describe the sensations they experienced during an orgasm, and doctors were unable to distinguish men's answers from women's.

For both sexes, orgasms last for only about 20 seconds. Still, their effects on a person's health can be long-lasting.

Studies have shown orgasms can reduce stress, improve sleep, decrease the risk of prostate cancer and endometriosis, and bring pain relief.

Scientists have many theories about why orgasms exist. Men commonly orgasm when they ejaculate. Because ejaculating can lead to pregnancy, some believe the male orgasm's sole purpose lies in reproduction.

Why women orgasm is less clear, Herbenick said.

A few researchers controversially suggest that orgasms act as a matchmaker for women. Mr. Right, they say, will make orgasms easier to achieve. Another theory claims that the contractions of the uterus during orgasm actually pull sperm into the uterus, therefore also assisting reproduction, but women don't need to orgasm to become pregnant.

Some people think it's just a sort of leftover characteristic that women have sort of like why men have nipples even though they don't need them, Herbenick said. In any case, while we sort it out, they're certainly a fun way to pass the time.