Originally Posted by
unterhausen
15 minute time trials you say?
There is an unending amount of discussion online and elsewhere about what makes for the most effective interval duration, frequency, and specific intensity for raising FTP. Some coaches recommend longer(15-25 minute), sub threshold (zone 3) intervals and others recommend somewhat shorter (4 to 8 minute) intervals a bit above threshold (zone 4).
Either can work, I am sure - what is probably most important is coming up with a formula that one actually doesn't mind doing so they actually get done.
Personally, I favor 1 or 2, 15-20 minute intervals done once or twice a week. With an intensity scaled back slightly to just below what i would actually race such a short time trial at. I basically have a few climbs and sections of road that I like to test myself on. For a person who does no speedwork otherwise, even if you did just one or two of these intervals a week, it would produce real gains in 'cruising speed' (zone 2 speed that you actually ride during randonees, etc.).