Stage 1: Excitement and arousal
When physical or psychological stimulation occurs, a man will get an erection which is the first sign of sexual arousal. This is caused by blood rushing to three spongy areas which run along the penis, called corpora. The skin of the penis is loose which enables it to grow – the scrotum, which is the skin that holds the testicles, also becomes tighter, causing the testicles to draw up towards the body.
Stage 2: Plateau
The head of the penis, known as the glans, gets wider during the plateau stage as the blood vessels within the penis fill with blood. As this happens, the colour deepens and the testicles grow in size, up to 50% larger than their original size. The perineum, which is the area between the testicles and the anus, creates a warm feeling – the heart rate increases, blood pressure heightens and his breathing will become more rapid. During this stage, the man is close to orgasm.
Stage 3: Orgasm and ejaculation
Semen is forced through the urethra by a series of contractions, which occur in the pelvic floor muscles via the vas deferens – this is a tube which carries sperm from the testicles to the penis. There is a stage during these contractions where a man cannot halt ejaculation.
Stage 4: Resolution
The recovery stage follows the orgasm, and it is during this phase that the testicles return to their normal size. Whilst still breathing heavily, his heart is being at a fast pace and he may also be sweating. There will be a stage following ejaculation where a man will be unable to have another orgasm, though this period of time varies between each person. As men age, this period of time becomes longer.