just another gosling
Join Date: Feb 2007
Location: Everett, WA
Bikes: CoMo Speedster 2003, Trek 5200, CAAD 9, Fred 2004
Mentioned: 27 Post(s)
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The 8 minute test is used because many riders find it hard to locate a place where they can go steady for 20 minutes, which is the more usual test, see the sticky on this forum. Outdoor field testing will often give different results than indoor testing, so Carmichael has opted to use a possibly less accurate outdoor test for simple, practical reasons. And IME, it works. What you are supposed to do is to TT for that 8 minutes, IOW ride as much distance as possible in 8 minutes. So you won't be shooting for a steady state HR. You'll keep ramping it up until you attempt to hit MHR at the finish line. All-out, just like it says.
So then you take the average for the whole 8 minutes, including the lower HR beginning and the higher HR ending. Remarkably, this average comports well with steady-state LTHRs obtained by the longer tests. It may take a few tries to get enough experience to do this without blowing up, which would give an inaccurate result. You can test your result on local long climbs, if you have any. It's understood that you'll have a good warm-up before you hit the start. So your beginning HR after warm-up will affect the result slightly, but the period of transitioning into a working HR is so short that I don't think the actual beginning HR affects the result much. When I'm ready to TT, I'll hit a working HR in about 200 feet. Hit it just like a racer coming out of the house.