Burning Legs & still eating

I've decided this year that for my under-50 minute bike rides that I'd do a 5/2/5/2/5 workout. What I mean by that is that after a warmup spin, I do a 5 minute +20 mph spin, then a 2 minute catch the breath spin, followed by a 5 minute +20 mph spin, etc. So far I've been able to complete the first two 20+ mph spins and the last one at 19+ mph. I sweat like crazy and my heart rate is pretty elevated during the 5 minute spin -- and when I'm done, the legs are burning pretty good.

Like they say -- no pain, no gain (I guess). The body is still needing that extra fuel -- still eating more that normal.