I recently did the CTS test (two 8-minute time trials, average power multiplied by 0.9 to get an estimate of FTP) for the second time since I started training 6 months ago, and, happily, my FTP (according to the test) had gone up quite a bit, from 237w to 256w. However, having completed my first interval session on my indoor trainer using this new FTP (4x10min @ FTP with 2min RBI), I'm starting to have doubts. Basically, it was hard. Really, really hard. By the third interval my heart rate was maxed out, I was dripping in sweat, feeling nauseated and seriously thinking about giving up. I did manage to complete the set, but my question is: Are FTP intervals supposed to be this hard, or has the CTS test given me an overly-optimistic estimate?