The foreskin is a membranous line, more or less thick, which is located under the glans and connected to the skin of the penis.
Typically, a short frenulum causes traction of the glans down. It does not really prevent the foreskin from retracting. A too short frenulum is a real handicap for young adults during sexual activities. Indeed, if a rather narrow brake is fragile and when the erection is strong enough, it can cause pain to the brake during penetration. The frenulum can crack or even tear with bleeding.
Discomfort from a torn frenulum may last for a few days after more intense sexual activity. It eventually heals after a few days of abstinence. But, unfortunately, often, the dynamic is repeated when resuming sexual activity.
In other young men, if the frenulum is wide and solid, it does not break but causes an impression of painful traction erection, sometimes responsible for some premature ejaculation.