You know when your forearms feel like they are going to burst open and you can't physically close your hand? How about when you get the elvis leg and start shaking all over? Or, better, when you go for the next hold and think "I'M SO PUMPED?" Well, by then you are probably off the wall.
The truth is, endurance is very mental. Sure, climbing laps and doing routes back to back, circuiting, and eating healthy helps, but in all honesty, that can be hard to do sometimes. So what do you do when you need an alternative method of holding on forever?
I let my mind do the trick. Trick, yes, because it is a bit of a self-convincing process. When I am climbing on a long route (I was just in Spain where my 100 meter rope wasn't long enough...) I need to forget about the anchor. Break the route down into segments. Find the rests and define these as your check points. At each check point you have a break where you can shake out. Maybe you are thinking that you are too pumped to shake out? Well, this is a problem because as soon as I think to myself "I'm so tired," then I am instantaneously so much more pumped. The trick is, distract your mind. Think of the sequences in front of you, sing a song to yourself or keep a mental rhythm going - a lot of methods work but through personal experience, telling yourself that you are pumped or that the next move is hard while you are on the wall definitely does not help. Instead, by focusing your attention on the sole movement in front of you, you can breathe easier, maintain attention, and climb much more precise. Allocate your energy throughout your body so that you are not only on your arms. Take a breath when you feel like respiration is heavy and go for it. Push onwards and upwards. As the Spanish say: A Muerte!