I don't think I stopped concentrating for the whole 3miles, I was knackered afterwards ;-). It's not PHYSICALLY hard, its mentally hard keeping the focus on the chosen element I want to focus on. I kept on stopping when I felt I was "loosing it" and then restarting. Claire has suggested I just keep going as it can be more effort to stop-start so I'm going to try this on my run today. What I WILL say is that when I got all the bits to work right ... my body felt it and it felt like I was floating. An amazing feeling.
Here is a link to my video before and after the techniques secession if you missed my post on Facebook.
If you have any more questions feel free to ask via comments below or facebook or twitter.