In porn movies how could they do sex for so long time ?

Are professionals: (1) They are trained professionals. (2) It's a movie. (3) They audition, and actors who don't pass audition don't get the part. (4) They need a disclaimer, WARNING: The following show features stunts or activities performed either by professionals or under the supervision of professionals. Therefore, the producers insist that no one attempt to re-create or re-enact any stunt or activity at home.