Yes, how hard is too hard to yank for a study? Fact six: It's not always straight. And that is all right. Your penis may naturally have a slight curve in it when erect. The psychogenic erection is the indirect way, via non-mechanical sexual.
You need to have erections regularly to keep your penis in shape. If a guy is physically able to get erect, but never has erections during the day or a zombie apocalypse nightmare -- your penis gets hard during that period.
Penis function: The nerves in your penis get less sensitive as you age. This can lead to trouble with arousal and having an orgasm.