I do gut wrenching wind sprints 2 or 3 times per week followed by a longish, 50 mile, weekend ride. Doing this I've scratched and clawed my way from near 0 to a 19.7 MPH bike leg of a 20 mile Triathlon. I'm 55 y/0, 5'7", and 205 so plenty fat.

My wind sprints consist of 60 seconds of all out effort followed by 120 seconds of rest. I warm up a bit and cool down a bit, total ride is about 30 minutes.

I tried doing a couple of 20 mile rides and the long weekend ride but it did nothing for speed.

Like BlazingPedals I enjoy the training and agree completely with his comments about the "dead zone".