I take the initiative to answer to your 2 good questions
To the first question I will answer that it depends.
But you are right. Your question is very pertinent. STAGNATION is a big issue in the running sport. Stagnation that´s so frequent, or more frequent as progress, because in one point of live your performances will stagnate if not retrograde. But why most of the coaches show their training which the goal that´s progress and the same good runnes they tends to ignore or forget to tell us about how to solve stagnation issue? I think that´s because in most of the cases the coach´s mind os focus in a winner philosophy and they refuse to face the shadow that´s stagnation and/or regress.
I alo know coaches that since they aren´t able to have some progress of the runner they coach they tends to give up that runner – and they want to ignore the failure that´s the absence of progress. How many coaches have write an article about the stagnation issue, or about the runners that trains according te coach schedule but that they haven´t been able to make some progress. In 30 years of running I didn´t read a single line about that failure tries. How many?
Coaches, runner´s and more they tend to omit that fact – that they did fail in some cases to have some progress, most of the times contrary to what they expect.
Let me say that I have some cases that I consider that I did fail to obtain the runner progress that earlier I did estimate, and in that aspect i´m disposal to do my auto critic if I consider that the failure that´s my responsibility
I said that it depends of the context and my it depends of what I will do in a stagnation case.
May be that I consider that the stagnation is due to something external to the training method – I try to fix the problem by that me or the runner changes that condition. But may be that I consider that the problem that´s a wrong/inadequate training schedule – I try to change that and move the training in another direction. If after sometime I see that despite the runner follows my training schedules he haven´t no sensible progress, may be I advise him to change from coach if he wants, because if that despite the failure the runner wants to be advised by me or haven´t other coach to help him – I continued to help him, try to find what change or what to insist in the same training standards. Sometimes we need time to see some progress. It happens a lot
May be that the runner is in his performance limits – we need to understand that we all have limits. Even Kenenisa Bekele have performance confinement. It will come one day that he willn´t do no more progress. This is a turning point in their career, or he gives up or he tries to polarize his career to delay that with move up to different event – usually longer ones, or that the runner it defines a different goal season – instead of try PBs, he will try to win races. Look for Tergat or Gebre. They aren´t the same performers that they used to be. They are old, but they try to move up from track and cross to road runs and marathon runs.
2. The most commons identifications of the overtraining are the poor answer to workouts, or to competitions, and also the running reactions that the runner reports, and eventually we need to have some data – blood analysis an important one and to see a doctor or doctor help.
Anyhow I tried to avoid that runners enters in overtraining. I´m known to be a coach that most of the runners they are able to resist to my workouts. Very rarely are the occasions that a runner aren´t able to finish my workouts due to tiredness or that we enters in overtraining. In my experience the training intensity, more than the training volume or anything else are the main reason to overtraining. One decision - in the terrain – if i´m there with my presence - that´s to reduce and end the workout or skip the workout(s) or the training session(s) that if you imagine that the runner is in overtraining or enters in overtraining. Sometimes, during no matter what training moment I use to have 10 days without no workout at all – just easy runs. The runner don´t need to train in the limits all the time.