Orgasm is reached through copulation or masturbation. During orgasm the body stiffens and the muscles contract. Involuntary muscle contractions and spasms may occur in various parts of the body, including your legs, stomach, arms, and back. The muscles of the vagina relax and contract rapidly, as do the muscles of the uterus. The glands of the vagina discharge a watery secretion , which acts to lubricate the vagina. The main physical changes that occur during a sexual experience are a result of vasocongestion.