I've done 26.2 doing walk/run intervals (4 minutes run, 1 minute walk). I have an ironman watch that "beeps" me when it's time to switch. I actually felt better and made better time than when I ran continuously and walked only through the water stops (and when I thought I might need to). Jeff Galloway is a great advocate for the walk/run technique (he's written a few books and also writes a column in Runners World) It works for me!!