After an hour or two of paddling, my legs go so numb that when I stand up
on the dock afterwards, I'm as likely as not to fall down again as my legs
collapse under me.

Is there some way to adjust my kayak seat to help my circulation?


Same thing used to happen to me. In addition to what Michael suggests, it
might be worth working on using good posture when you sit in your boat, and
when not paddling, work on keeping your lower back muscles strong and
stretched. Many times, leg problems stem from back problems. Worked for
me, anyway; just my $0.02 worth...