I don't know my FTP or how I would measure it. I seem to recall reading in someone's post that 85-90% of FTP is a good 'zone' to be targeting for these intervals.

Qualitatively how hard would you describe this kind of effort? Do I basically want to be going for the most power (effort) that I can sustain for the 2x20 minutes with a (5?) minute gap in between?

Thanks in advance for answering this noob question.

you should run a search, plenty of info on the subject.

2x20 are typicaly done at 95-100% of FTP.

Are you training with power? heart rate& Perceived effort?

As a general guide, here is how I perceive a 2x20 workout at 100% FTP

- first 5min are quite easy, very doable (5-10W below FTP)
-5 to 10min: a bit harder but still plenty doable (5W below FTP)
-10 to 15min: I generally had a bit of resistance and up my power a bit, 5-10W no more (bang on FTP and even 5W over it)
-last 5min are pretty hard, I once again generally increase resistance on my trainer (10-20W over FTP)

I developped this pacing strategy over the years, and it works very well for me, in fact, it gives me very accurate numbers, always hitting spot on 100% FTP for average power

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Thanks, that's the kind of description I was looking for.

I don't have a power meter since I'm a newbie, a student, and they are outrageously expensive.

FYI I started with a wired SRM unit and they are not so expensive. They are all used and often can be found for 600-1000 $cad and they are damn reliable, accurate and nuclear proof.

enjoy the training!

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2013 rocky mountain vertex 29er
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+1 what devinci said. I went wired at first and they can be had for cheap on ebay.

Hmmm. Personally, I believe that the intention of the Interval is to come close as you can to maintaining your wattage throughout the Interval. It is much more difficult to do this than to 'average' to your target wattage. My normal process is to try to hold to my target wattage, then let-fly in the last minute.

I have SRM Interval files from pro riders that demonstrate this principle (although, seeing that kind of power is very humbling).