When you’re excited or experiencing desire for your partner, your heart rate and breathing accelerate, your skin might blush, and blood starts flowing to your nether regions to facilitate an erection and swelling of the clitoris. Women’s nipples will harden and their vaginas might become lubricated, while men’s testicles may swell with lubricating liquid as well. Your muscles, at this stage, respond by tensing up.
During the second stage of sex, your muscle tension might become more pronounced. This stage is also accompanied by a general heightening of all other sensations felt in stage one, along with other changes like the darkening of the vaginal wall, retracting testicles, rise in blood pressure, and an extremely sensitive clitoral region. One might even experience muscle twitching or trembling at this point, in their feet, face, and hands.
When you have an orgasm, which is stage three, your muscles respond to this peak of sexual experience by involuntarily contracting to release the pent-up tension that has been built up thus far. This is also the point at which your breathing, blood pressure, and heart rate are at their highest levels. During the process of ejaculation, the muscles at the bottom of the penis constrict and expand. For women, the vagina and uterus muscles contract. It is only after this stage, stage four (resolution), that your muscles begin to relax. Your swollen genitalia return to their pre-sex state, and you feel spent yet calm, satisfied, and relaxed.
