Agree with Corn and MS.
The whole overtraining issue is complex and not well defined, but many of us have experienced it in some form.
MS is correct in that a single bout of heavy eccentric arm work is not going to result in systemic overtraining, but will cause force decrements to persist in the worked muscles for some time, even after the soreness resolves.
Repeated bouts of heavy exercise involving large muscle groups over time can result in overtraining (i.e., feeling fatigued, lacking drive to train, increased colds and illness, muscle pulls, joint pain, depression, sleep disturbances, irritability, etc.). It is also important to realize that everyone has a different threshold and that’s why a coach has to tailor and monitor the training load for each athlete even within a given event. For some, they can train heavy frequently and never have problems (those are the ones that say OT doesn't exist), for others OT occurs fairly quickly. If sleep and diet are optimal, and the symptoms of OT begin to appear, it is time to take a week off then start back in easy, taking a few weeks to get back to the original work load. What gets most of you in trouble and limits gains is the inability to take a week off of everything and just go for walks.
It is also important to be careful after a cycle. This is a time when you are lowering the body’s ability to deal with physical and psychological stress. If one continues to try and push juiced training loads and intensity, injury, illness and depression are likely to occur.
W6