This is wikipedia/Human_sexual_response_cycle , converted into an erotic short story by pruning some less sexy parts, approximately changing ‘male’ to ‘his’, ‘female’ to ‘her’, and changing from present to past tense.
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Their sexual response cycle
Their response cycle was a four-stage physiological response to sexual stimulation, which, in order of their occurrence, were the excitement phase, plateau phase, orgasmic phase, and resolution phase. Their cycle was first described by William H. Masters and Virginia E. Johnson in their 1966 erotic novel Their Sexual Response. Since then, other sexual responses have been experienced.
The excitement phase was the first stage of their sexual response cycle. It occured as the result of physical or mental erotic stimuli, including kissing, petting, and viewing erotic images, which lead to sexual arousal. During the excitement stage, their bodies prepared for sexual intercourse, initially leading to their plateau phase. Physical and emotional interaction and stimulation of their erogenous zones occured during foreplay, establishing initial arousal.
For both of them, the excitement phase resulted in an increase in heart rate, breathing rate, and a rise in blood pressure. Their sexual arousal arised and was enhanced by mutual direct stimulation of their nipples. Vasocongestion of the skin, which they came to refer to as the sex flush, occured in them. During her sex flush, pinkish spots developed under her breasts, then spread to her breasts, torso, face, hands, soles of her feet, and over her entire body. Her clitoris and the walls of her vagina darkened. During his sex flush, the coloration of his skin developed less consistently than in hers, but started with his upper abdomen, spreading across his chest, then continued to his neck, face, forehead, back, shoulders and forearms. The sex flush stayed until disappearing after their orgasm occured, after two hours or so. Intense sweating occured simultaneously.
An increase in muscle tone of certain muscle groups occurred voluntarily and involuntarily. It began during the excitement phase for them both. Also, their external anal sphincters contracted randomly upon contact, and later during orgasm even without contact.
For him, the beginning of the excitement phase occured when the penis became partially erect, after only a few seconds of erotic stimulation. The erection was partially lost but regained repeatedly during the extended excitement phase. Both testicles became drawn upward toward the perineum. Also, the scrotum became tense and thickened during his erection process.
In her, the excitement phase lasted several hours. The onset of vasocongestion resulted in swelling of her clitoris, labia minora and vagina. The muscle that surrounded her vaginal opening grew tighter and her uterus elevated and grew in size. Her vaginal walls began to produce a lubricating organic liquid. Meanwhile, her breasts increased slightly in size and her nipples become hardened and erect.
The plateau phase was the period of sexual excitement prior to orgasm. The phase was characterised by an increased circulation and heart rate in them both, increasing sexual pleasure with increased stimulation, and further increasing muscle tension. Also, respiration continued at an elevated level. Both of them began to vocalize involuntarily at this stage.
During the plateou phase, his urethral sphincter contracted, and the muscles at the base of his penis began a steady rhythmic contraction. He started to secrete pre-ejaculatory fluid and his testicles rose closer to his body.
The plateau stage was for her a continuation of the same changes evident in her excitement stage. Her clitoris became extremely sensitive and withdrew slightly, and her Bartholin glands produced further lubrication. The tissues of the outer third of her vagina swell, and her pubococcygeus muscle tightened, reducing the diameter of the opening of the vagina.
Orgasm concluded the plateau phase of the sexual response cycle and was experienced by both. It was accompanied by quick cycles of muscle contraction in their lower pelvic muscles, which surround both of their anuses and their primary sexual organs. She also experienced uterine and vaginal contractions. They had other involuntary actions, including vocalizations and muscular spasms in other areas of their body, and a generally euphoric sensation. Their heart rates increased even further.
For him, each ejection was accompanied with continuous pulses of sexual pleasure, especially in his penis and loins. Other sensations were felt strongly among the lower spine and lower back. The first and second convulsions were the most intense in sensation, and produced the greatest quantity of semen. Thereafter, each contraction was associated with a diminishing volume of semen and a milder sensation of pleasure.
The overall sensation for her was similar to that of his. She had an increase in vaginal lubrication, a tightening of her vaginal walls, and overall pleasure.
Source: reddit.com/r/eroticliterature/comments/4rauzr/their_sexual_response_cycle