I did Tabata type workouts once a week starting a few weeks before crit season last summer. I usually did two sets of 6x20"on/10"off. The 'on' was an all out sprint - I am sure by the last couple of on intervals my power was way down but I thought this was the idea. It sure felt like a good workout for crits, but what do I know since I don't have a power meter? Another plus is that it fits well into a short lunch ride.