I think this is meant in general. He talkes about that horses can feel it boring if you do it too often.
After I did my first Join-Up I did not do the next until it was really necessary (about five weeks ago, because I scared him to much with a gymnastic ball; I have done my first one in September last year).
Jasmin

It really does depend on the horse. Four to six is average for a horse, but it does depend on the horse's attitude. If you do one or two and it is obvious by the horse's calm attitude and cooperative manner that you have established the communication and trust you are aiming for, then good. Look for the positive change in the horse--that is what you are aiming for with J-U. You don't have to rotely do more--that's like having the same conversation with your child when he's gotten the point and is complying. It's certainly ok to do another to reinforce things after a scary incident, or once in a while as a review for both of you. I've done probably about a dozen with my mare over the course of 3 years, more as practice for me than because we needed it. Shy Boy's done thousands over the course of the time he's lived with Monty and he's a great horse to learn J-U with, as he knows exactly how it should go and won't come in to you unless you do it right :). It won't hurt to do a lot, just don't feel you need to do more if you feel you have the end result you are looking for. Good luck and have fun!

Thank's a lot for that advice!! But at the moment I have been doing some work with the dually halter and Monty reccomends doing a Join-Up before each session. There are a lot of dually excercises that I want to do but I cant do them all at once so that would mean we would have to do quite a few Join-Ups. Does that matter?

I have never noticed that Monty said something like this. In which video is it? Maybe you are missunderstanding something?