Possibly a question for Serpico, or anyone else with an interest in sports physiology;
The anaerobic threshold, if I understand correctly, depends on the capillary density in one's muscles, and their ability to deliver oxygenated blood to the muscles, and remove excreted products of respiration.
According to texts such as PRC and SCC(and Fluxus' posts on RC.com), the only effective way of increasing capillary density in the forearms, in an applicable way to climbing, is with ARC-type training.
If someone were to have relatively sparse capillarity in their forearms, and so get quickly pumped on the easiest of sequences, would the presence of all that lactate and blood, not mean that a certain amount of extra capillarisation occur, in the muscles, to aid recovery of those tissues?
Apologies for my basic level of understanding, it is years since my physiology lectures (I'm a GP!)
I only ask, as I am climbing again, after a layoff of several years(don't ask!), and I can't seem to even traverse, for long, on jugs on a vertical wall, without getting very pumped.