This is our ability to climb a without getting pumped, as a result, the aerobic energy system can keep going almost indefinitely. However, it only generally works up to around 40% of the maximum effort an individual muscle can produce. Above that and we start to produce and accumulate blood lactate and start to get pumped. Aerobic Endurance is the same system that helps us to recovery on the route by helping get oxygenated blood to our climbing muscles and at the same time flush lactic acid away.
Generally, we can improve our aerobic endurance by climbing a high volume of routes or boulder problems below that magic 40% effort. The results of this are to push as much blood through the active climbing muscles, over a period of time this results in the widening, reinforcement and even creation of capillaries in those climbing muscles. Although getting stronger will also arguably increase Aerobic Endurance as the moves become ‘easier’.
In terms of training principles, Aerobic Endurance is a good place to start and is usually the initial phase on a 14-week periodised training plan. However it can just be a a focal point for a 4-week training block.