I've heard that it's the quarter, but i'm not so sure. Problem with sprint events being harder than distance events is that many sprint championships have multiple heats like the prelims and the quarters in the same day. I'm not knocking sprinters or the training, but I feel it's a lot easier to run 2 100's or 200's in the same day than 2 1500's or 5000's. I personally think the marathon is the most painful event simply because people collapse and even die from this damn race. Yeah the 5 and the 10 is hell, but not too many people drop dead after the race. I say the marathon. What about you?