Basic Types of Sexual  Behavior

2. Heterosexual Intercourse: Genital Intercourse

Coitus

Techniques of Coitus 2
Men with limited sexual experience may believe that unvaried, deep, and quick thrusts are the most effective, but in actual fact this is rarely the case. At least at the beginning of coitus, a man can give and receive much more pleasure by moving slowly and keeping the penetration shallow. Indeed, he may learn a great deal by first leaving the initiative to the woman. In most cases, she will prefer long and deliberate movements in which the tip of the penis is withdrawn toward the vaginal opening before each new deep penetration. The reason for this is simple: With mounting sexual excitement, the inner portion of the vagina widens while the outer third narrows as it becomes congested with blood. In other words, it is the outer third of the vagina (the so-called orgasmic platform) which provides the greatest stimulation for the penis (see "The Female Sexual Response.")
Iit sould also be mentioned that many women learn to control the interior muscles surrounding the vaginal entrance. Thus, they keep a firm grip on the penis and increase the mutual stimulation even further. (Women who have a wide and slack vaginal entrance, who are unaware of their vaginal muscles, or who find them underdeveloped, can improve their condition by appropriate exercises (see "The PC Muscle”).

The pubococcygeus (PC muscle)