Verb
overtrain (third-person singular simple present overtrains, present participle overtraining, simple past and past participle overtrained)
(transitive, intransitive) To train too much or too long.
Jim overtrained and found that he was exhausted by the time of the competition.
I think I've overtrained my leg muscles.
If a person follows a clean Paleo diet (i.e. no sugar/grains/diary/legumes/*) and sleeps long enough and doesn’t overtrain, etc. then everything should be OK. Source: Internet
Unless you have fantastic genetics many people overtrain. Source: Internet
One article published by Muscle & Fitness magazine stated that you can "Overtrain for Big Gains". Source: Internet