The penis is close to the belly when it is erect

Male genital erection is the "preparation position" for sexual intercourse, but even men may not fully understand why it becomes hard.

When the penis is erect, it is close to the abdomen

The hardness of the penis is divided into four levels: Level I is not hard at all. Level II is partially hard, but cannot be inserted into the vagina. Level III is erect and can be inserted into the vagina, but there is no swelling. Level IV is very hard and there is swelling. When the penis is erect, it is best to put it against the abdomen.

Humans have three erection mechanisms. First, psychological erection. When a man is exposed to sexually related stimuli such as hearing, vision, smell, and imagination, the cerebral cortex is excited and acts on the cavernous body through nerve conduction, which will cause blood vessels to dilate, and a large amount of blood will be injected into the cavernous body, causing the penis to quickly become psychologically erect. On the contrary, when blood vessels contract, the blood flow into the cavernous body decreases; venous capillaries dilate, and the rich blood stored in the cavernous body of the penis quickly flows back, the penis will restore its softness.

Second, reflex erection. When the male genitals are stimulated by direct touch, walking friction, etc., or receive stimulation from the duodenum and bladder inside, reflex erection can occur. This is caused by stimulating the spinal cord erection nerve center and stimulating its sexual impulse. Penis erection is innate, and male fetuses can get erect in the womb. Boys may also get erect when urinating after they are born, but the erection at this time does not have any "sexual" meaning.

Third, nighttime erection. Men's sleep quality is always in the alternation of REM sleep and SRM sleep, and also goes through the physiological process of erection-softness-hardness-softness again, which is called nocturnal erection of the penis in medicine, and is a normal physiological process for healthy men. Generally speaking, men have 4 to 6 erections every night, each lasting 20 to 40 minutes, and a total of two and a half hours of erection. This is because the human brain has an inhibitory response during the day, but after falling asleep, the inhibitory effect of the brain disappears, and the penis spontaneously has an erection response.

The duration, frequency, and intensity of nocturnal erections decrease with age, and are strongest during puberty to around 20 years old. Whether it is a psychological or reflex erection, the penis quickly returns to normal after the external stimulation disappears. Nocturnal erections are not an exception, and the penis will automatically soften after a period of erection.

Morning erection is a more meaningful physiological phenomenon in clinical medicine. Some experts and scholars have studied this phenomenon professionally and scientifically and found that during the illness period, the morning erection will weaken or disappear; after the body recovers and is treated, the morning erection will also recover. Therefore, the morning erection can be used as a reference indicator of men's physical condition and can also be used as a reference indicator to judge men's sexual function.