Originally Posted by anotherbrian

If you want to stay aerobic during those climbs, get even lower gears then. Or ride hills that are slightly less steep.

Yesterday I rode the Sierra Century in NorCal, and after hearing too many stories about "Slug Gulch", an allegedly ~5mi grade at 15%, I put an MTB cassette and RD on my road bike. It turned out the climb wasn't nearly as bad (it was 5mi long, but the first half was only ~10% with short 15%'ish bumps). I used all the gears I had and was able to spin (75+) the whole way while keeping my HR at 80% of max. A few people crept passed with trad road gearing, and besides the 50'ish cadence, they sounded like they were absolutely dying.

If the ride is short, or I'm close to the end, or it's part of the training plan, I don't mind doing all out anaerobic efforts. To keep things enjoyable, they're better done on my terms though. And for sure, you don't need to ride hills anaerobically all the time to improve your fitness and make them easier ... just increasing your aerobic capacity will do wonders.