When I'm on an exercise bike, I find that the first ten minutes are by far the toughest. When I go on the bike, I alternate between cycling fast and then even faster at regular intervals. In the first ten minutes, I'm out of breath and if I haven't been on the bike for a while, I'm unable to get through this initial ten minute period. But if I can get past that, my breathing settles down and it becomes much easier. Why is that? This evening I was on the bike for 45 minutes. When I came off my heart rate was high, I was dripping sweat, my legs ached, I was saddle sore but I wasn't really out of breath. What is that makes that first ten minutes so much harder than the rest?