Normally I run 1 hour every day without taking breaks. After reading posts about overtraining, I am worried that I am doing that. How long can we run without over training?
No one can say how much you can train before you become overtrained. Firstly, there are too many factors involved, such as nutrition, weather conditions, your cardiovascular fitness, your fat percentage, your strength and explosiveness, the presence of any diseases (in particular autoimmune or inflammatory). Even if science knew how all those factors affected training capacity, and how much, there is still the individual factor. Your personal biochemical profile; level of cortisol and how quickly it rises, testosterone and growth hormone, enzymes and proteins at the cellular level.
This is the big problem with the overtraining syndrome; no one can really know beforehand how much he/she can train. It is only when you start experiencing symptoms of overtraining that you can begin to titer your training down to maximal, but safe, levels.
One simple thing thing that you can do is to measure your morning heart rate. It's simple, and everyone has the equipment for it. Keep track of your morning pulse every day, and if it starts going up about 10 beats on average for 3-4 days, then it's time to rest or decrease training intensity (I speak from my own experience. For you the numbers may be different, however the principle is the same). I had overtraining syndrome a couple of years ago, and of all the symptoms, the most objective one, that I could gauge, was my morning heart rate which was around 80 instead of the previous 40-45. Since then I have kept track of my HR every day.
So to sum up: you can't know how much you can train before becoming overtrained. What you can do however is to keep track of your fitness and recovery levels. This is most easily and objectively done by measuring changes in the morning heart rate.