I have been really worried about this one so much so I did W5r2 3 times !! Was just worried I would not have enough in the tank as I am an old lady (54). But as always just "trust the plan " as Laura says and she was right. I probably could have gone further as I seem to gain strength as the time goes, the hardest bit for me is always the first 5 or so minutes. Part of that may be the terrain ,but I'm not quite sure cause I even feel that way on a treadmill. Anyway I'm just so pleased to have done it !