I watch the shows to get a sense of the type of physical shape these guys must be in. From the Detroit SWAT episodes, I think they had to be able to do 20 pull-ups, 60 push-ups full range and run 1.5 miles in 10 minutes; they get re-tested every 6 months. If that's correct from my memory, that's not easy to do. These guys are clearly in better shape than I am. That's not saying much, but the comparison provides me a reality check.
Apparently, SWAT is supposed to be the top notch of state law enforcement, and each member has to be invited first. From watching the SWAT and DEA shows, I have a better impression of SWAT teams than of DEA teams.