I tried to do a century this week and couldn't do it. The endurance just isn't there yet. At about mile 65 my heart rate had drifted up to 150 and as I lowered my effort to keep my HR from going higher it was apparent that I was in for a miserable time. So I called 75 miles good.
Over the three months of July, August and September which I called my pre-base phase I progressed from zero in June to 177, 349, 558 miles; 18:30, 32:50, 40:00 hours training; 1200, 2130, 2260 TSS; and 5400, 11,400, 16,000 KJ. Most important is that my TSS went from a low of 25 on 7-17 to 65 on 9-30.
All to say I am ready to start building endurance and power. In my last entry I gave some wrong numbers on FTP. I actually lost 60 watts from my peak FTP of 230. I come into October at 191 having climbed back a little from the FTP of 170 in early July. Increasing FTP 39 watts is hugely challenging. It took me months to push it from 217 to 230. Hard, hard work ahead.
As an aside, Joe Freil writes that you can calculate your potential FTP by taking your weight, doubling it, and subtracting half a percent for every year over 35 you are. So for someone weighing 170 pounds and, call it, 64. FTP = 340 - 14.5%*340 = 290.