Hi Jeff,
I am not one of the faster runners on the blog, but I have just about every running book ever written (including the ones from the 70's/80's -- Running to the Top is one of my all time favorites) - because I am a research geek.
The best "explaination" I have heard about LT pace, when you don't have access to a lab to measure it, it is the pace you can comforably run a fairly high intensity for an hour (by the end it feels like you are at tempo pace). For slower runners, like me, it is somewhere between 1/2 marathon to 30K race pace; put another way it is 85-90% of your maximum HR. AT pace is harder to judge, some of my friends swear by the Conconi test (there is a good website on this
http://www.brianmac.co.uk/coni.htm or
http://web.inter.nl.net/hcc/j.vd.bosch/congeneral.html) if you have a hrm.
www.mcmillanrunning.com has a calculator (under running calculator tab) based on a recent race (note that this should be a race you have run, not a target race). Steady-state pace is LT pace and the Speed workouts are approximate AT paces.
Good luck,
Bonnie
