Many of us try to fit in so much in one day that when it comes to training we are exhausted. How do we know the difference between everyday stress and over-training? What are the signs of over-training?
If your heart is still racing afterwards that is a really bad sign. I know people that workout so much that they literally vomit afterwards. If that is happening to you then that is a sure sign you are overdoing it. It's best to start out at a slow, short pace and gradually build up. Overdoing it will seriously effect your health and could even put stress on your heart and lungs.
In addition to the answers given, I would also look be wary of regular injury. Whilst I don't think I am ever going to be guilty of over training (too lazy), I know that too much of one form of exercise seems to increase certain injuries. To avoid this, I try to mix up the type of exercise that I do so that I'm not constantly straining or stressing the same muscles, joints etc.