I did a 5k (it was at a park, no blocking traffic thank goodness) while walking at a normal to brisk pace. Done in less than 40 minutes. No sweating, no exhaustion, just a nice short walk.  My friend and I started a few minutes late. We were the first to cross the "finish line" by like 2-3 minutes. So we grab some fruit and water and talk about our actual workout later on.  The sheer exhaustion some of these fatties experienced was unreal. Here we are talking about hiking for a few hours or more and these fatties are ready to go lie down! At like 12:30 in the afternoon!