The whistle blows. I'm racing along with the pack, keeping an eye on the jersey in front of me, barely aware of the rider behind me. My pace is steady and the obstacles are manageable. Then suddenly I notice that my breathing is a little forced. I'm taking larger gulps of air and trying to calm them down by breathing through my nose. I ignore the discomfort and keep on. Half a lap later my gasping is so loud that spectators can hear it. Instead of cheering they pause and listen. They know that something is wrong. They might even spot the problem before I do. In my mind I'm thinking: It's a race. It's supposed to be hard. There is supposed be pain. I'm pushing the pace. I'm focused on a goal. It is within this mentality that I am often the last to acknowledge what is happening, I was hyperventilating. My lungs were restricting, closing up, depleting the oxygen that my muscles desperately needed. I was growing weaker, getting slower. The obstacles be...