No way, in a Cat 5 crit, you just ride around in a big pack. If you're in the middle of that pack, you're pushing maybe 50 watts. There's no real exertion until the final sprint, where mayhem ensues. Cat 4, maybe there's a few people organized enough to make a breakaway and you have to do some actual chasing. Road races are different, especially w/ hills, you can get dropped on climbs if you're not pushing.