I am currently training for my second HM. I did my last (and only ) one HM using run/walk and during training struggled out to 20K before the "race" . This time I am intending to go longer - but slower -- out to 24K before the "race". Race is in inverted commas - because it isn't really a race for me, more like a survival course!!
Did 18K last week and will do 20K next week. But the very fact that I am planning such a thing - traverse 20K on foot, partly running partly walking - is actually quite mind boggling to me. As John Bingham says - the miracle is not that I finished, but that I actually started!! I feel good about it though - even as I realise that I will soon be entering uncharted waters.