"base" with a teammate at lunch. We hit one hilly side of our rectangular loop all-out for 13.5 minutes. That hurt, but feels great now.
Happily, my teammate was able to drop me on this one and take about 20 seconds out of me -- he took about 7 months off the bike and has been back on for 4 months now, and this is the first time he's handed me my ass.
So much better training when you go into build if you and your training partner are trying to rip off each other's legs and get to trade success back and forth.