Grow Max Pro these effects make sex feel good. We also take a look at why sex might not feel good. Effects of sex on the body In the 1960s, sex researchers William Masters and Virginia Johnson identified four distinct phases of sexual arousal, each with unique effects on the body. Their research has led to the common use of these four categories to explain sexual response: 1. Desire or excitement The pleasurable sensations a person feels during sex come from many different parts of the body. During the desire phase, the tissue in the penis, vagina, pelvis, vulva, and clitoris fill with blood. This increases the sensitivity of nerves in these areas of the body. This blood flow also creates a fluid called transudate, which lubricates the vagina. Muscles throughout the body begin contracting. Some people breathe more .