The hymen or vaginal corona is a tissue, usually doughnut-shaped, inside the vagina. They don't "break" or bleed, but some of the hymen can stretch or tear. It is
normal for some of the hymen to wear away due to
normal activities such as bathing, masturbation, even just moving around or stretching. Contrary to popular belief, it is actually
pretty unlikely that a hymen
will be damaged by riding a bike or a horse, because all these activities really do is
put pressure on the perineum, not interfere with the vagina itself. It does not completely cover the vagina; if it did, menstruation would be impossible for girls with intact hymens. By the time full PVI occurs, the hymen is (usually) already mostly worn away.