This is the first time I've ever thought of running in a marathon (actually the half however it's full so my DH is trying to convince me to go all out and do the marathon). Anyway, I'm reading about sweepers. What are they? I have never trained for such a thing before. How far out do you normally start? I just started walking to lose weight about 2 weeks ago and am about 40 lbs overweight. I don't want to kill myself but what better motivation than running/walking through the parks?