Fat Boy

It depends what you're trying to do as far as how long the rest period should be. When doing sprints like WR is talking about, you want to be able to turn out max power. Now, his max power makes mine look pretty lame, but it's all relative. With this workout you are trying to recruit as much muscles mass as you can and tax it as hard as you can. If you're fatigued at the beginning of the sprint, you won't get the type2 A&B muscles working, and they are what will be the determining factor in your sprint. I did these when a little tired a couple weeks ago, and only got 2 in before calling it a day. When fresh I have done 6-7. They aren't easy and doing them poorly is probably worse than not doing them at all.

When training yourself to put up with surges, accelerations, and general crit activity, you need to work more on the your ablility to clear metabolized fuels (lactate, H ions, whatever it actually is). This is a completely different type of workout. With these a 15go/15off or 30go/15off is really effective.

I also do a workout I call 'rev-outs'. I ride in the small ring and a big cog. Starting from about 8mph, I accelerate absolutely as hard as I can for 12 seconds. I spin up to about 140-150 rpm in each gear before shifting up and can get through probably 4-5 gears. Then I take the rest of 2 minutes off. This is done specifically to recruit type2B fast twitch muscles. The big off period is to give them time to get ready to go again. If you do them closer together, it doesn't have the same effect. The good thing about these is that you can do maybe 10 of them, take a 5 minute recovery, and then do a 15s/15s or 30s/15s and get 2 completely different workouts on the same day. You're taxing different muscles groups, so the workouts compliment each other.

It's a matter of different horses for different courses.