Originally Posted by Chris Pringle

I believe your core muscles are weak. I went through this several years ago. I couldn't explain why I would get so tired so quickly in extended climbs experiencing the typical lactic acid build-up that makes your legs burn in pain. On your days off, try core exercises at your gym or at home. Pilates is a good one but there are other methods. You need to be careful if you go solo at home, since many core exercises could easily hurt your back if not done properly (best to start at the gym with an instructor.) You should see really interesting results in your climbing ability in approx. four weeks, as long as you stick to 3 times/week core training.