Overtraining is constant, intense training that doesn't allow enough time for recovery. Physical signs of overtraining include decreased performance, increase of musculoskeletal injuries, lack of energy, poor sleep patterns, muscle soreness, headaches, and loss of appetite. The psychological and emotional signs of overtraining include depression, apathy, reduced self-esteem, and difficulty concentrating.
More: Common Running Mistakes - Overtraining
Why Do I Feel So Tired and Sluggish?