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?

don't know about ftp, but doing intervals indoors, or any sustained hard effort indoors - I'd be really surprised if you DIDN'T feel nauseated...
BITD, when we used to do 'club' indoor sessions on rollers, it wasn;t unusual to have riders almost pass out, heavin chunks was also common for many who ate something within an hour of an indoor group session. And we used to have one of those big commercial stand fans to create some wind.
without the evaporative cooling of riding outdoors, it's easy to put yourself into major heat distress.

cyclezen, thanks for your reply. I may have to invest in a bigger fan...

What kind of training have you been doing in the past 6 months since your previous test? Most people find it harder, at least initially, to make the same power indoors on a trainer as they can outdoors. A big fan helps but even with that the trainer feels different and takes a while to get used to.

Whether you do an 8 min or 20 min or 60 min FTP test, at the end of the day it's just a number used to provide guidance for your training workouts. It sounds like you haven't been doing many interval workouts. I would suggest you repeat the workout at a slightly lower power and see how that goes. If you keep them at the same power level you will end up dreading the workouts and skipping them.

I don't know what you're training for but it sounds like too much intensity at this time of year.

As far as I understand it, you should have nothing left in the tank whenever you do that kind of thing.
I'm new to this training thing and the trainers raised my numbers by 30 watts in one week because they were initially too low and now it's really crazy hard keeping up with it but I can still manage even though I want to quit instantly and my legs feel destroyed while I'm no the bike.

They feel fine the next day so I figure that it's not so bad. So if you're feeling ok the next day and you aren't hurting yourself, then yeah... it's supposed to be really hard. As hard as you can tolerate.

4x10min @ FTP is going to be pretty tough no matter how you slice it. Think about it, FTP is your max power over the course of an hour (meaning riding until you feel like you'll die if you're doing it right), so 40 minutes of that isn't going to leave you in a much better place. I would shoot for 4x10 min at 95-100% ftp rather than right at it. The great thing about it, is once you start feeling like 4x10min @ FTP isn't killing you, it's time for another test... and then it kills you all over again.

So yea, it doesn't get any easier.

Thanks for the replies, guys. Sounds like it is indeed supposed to be this hard, which means I guess I'll just have to HTFU;-)

Yeah, that's what I would have thought too. I'm doing the second phase of a base-building plan from Trainerroad.com. I think the reason for the high intensity is the low volume (only 3.5 hours per week). But, until now, "high intensity" has been mostly sweet spot and tempo. Now it's getting into FTP (threshold?) intervals, and it's a bit of a shock to my system.

They should be hard but you shouldn't fear them. Breathing at all times should be deep, steady, hard to talk, but if you are panting during them then you need to back your power down a bit because you are probably in zone 5.