SOOKIE: What on earth were you thinking?
LORELAI: That I could still skate.
SOOKIE: It’s not like riding a bike you know.
Sookie is referring to the common phrase that a skill that is once learned and never forgotten is “just like riding a bike”.
Opinions vary as to whether ice skating is just like riding a bike – some people say they easily picked it up after decades off the ice, just a little wobbly to begin with. Others find that after a long break from skating, they have no idea how to balance any more and have gone back to beginner status. Sore legs and feet are common, just as Lorelai is experiencing.
The Annotated Gilmore Girls 