True overtraining is a reduction in power. In terms of weight lifting, what I read described overtraining as doing 2-a-days on the same muscle group for weeks until your 1-rep max actually decreases by 20%. That's over-training, and the cure at that time is 2-weeks rest, after which you will be stronger at 1rm than you were prior to the training period.

I don't think most of us get anywhere near clinical levels of over-training.