From Encyclopedia of Sex and Sexuality
In the early 1950s Dr. Arnold H. Kegel, a gynecologist, devised a series of exercises to strengthen bladder control for women suffering from incontinence. Control is enhanced through exercises of the pubococcygeal muscle, sometimes called the “PC” muscle. Sex therapists soon discovered that the same exercises also enable many women to feel more actively involved in the coital process by enabling them to tighten the pubococcygeal muscle during intercourse. They report an increase in stimulation not only to their vaginal areas but also to the penis of their male partners. Many women who have undertaken the Kegel exercises report they are more likely to have orgasms during intercourse.
A quick method for women to identify and learn how to exercise the pubococcygeal muscle is to urinate, stop the flow of urine, and then urinate again. After a few repetitions, most women are able to tighten this muscle without the involvement of urination. In another method for learning the Kegel exercise, the woman places one of her fingers about two inches inside her vagina. The muscles in her vaginal area are then contracted just as if she wanted to stop the flow of urine, and she will feel the pubococcygeal muscle tighten around her finger. She continues to contract the muscle tightly for a few seconds and then to relax it, repeating the exercise many times in a session and as often as possible during the day. Since this is a simple exercise and can be accomplished without the fingers once the muscle is identified, it is an especially effective aid in sex therapy. The toning of the pubococcygeal muscle can be achieved rather quickly, allowing a woman to feel confident about developing control and skills during coitus.
Devices known as “Kegel Exercisers” have been developed. These appear to be little more than dildos and there is no evidence that using a resistance-producing device, or even the fingers, as a form of resistance produces better results than the simple squeezing of the pubococcygeal muscle without any insertion once muscular contractions have been learned.