Endurance training - The easy and boring way

Training/Jens: Your endurance will improve if you can increase the blood circulation in your forearms. That lets your arms work with more fresh blood, and gets rid of the used blood. So how do you do it? By 1) creating new capillaries, and 2) increasing the the size of old capillaries in your forearms. You accomplish this by simply climbing as much as possible, on very easy terrain. You should not get pumped. Getting pumped is a sign that you don't have enough blood circulation. But you should climb as hard as you can without getting a pump. The blood circulation produces small pressures in your forearms, which creates new capillaries and increases the size of the old ones.