What's the best way to increase aerobic capacity. I don't need more speed, have never experienced lactic acid buildup in my legs and have never had soreness from a ride, but a ride of 30+ miles at 18-20 mph leaves me feeling completely wiped out for a few days. Rides of less than 20 miles at 20+ mph are no problem, even several a day. Anaerobic training is easy, you destroy the muscles, eat, rest, and they rebuild stronger than before. But for some reason the whole aerobic thing completely escapes me and I can't find much information that is not sport specific. The heart and lungs don't seem to appreciate the anaerobic strategy, at least mine anyway. How many days a week should you push hard, how hard, how much recovery is required, is active recovery always better than complete rest?