Training is always a delicate balance. You overextend a little so when your body can recooperates it comes back stronger than before. However, over do it too much and bad things can happen. I just got sick for the 3rd time this year -- I never get sick . I've figured this is a result of overtraining.
Classic overtraining symptoms include: increased resting HR, lethargy, lower motivation, etc. How do you recognize when you are at the edge? How do you prevent yourself from overtraining?
Multiple injuries are also a sign of overtraining, but for the regular folks, fatigue, and decreased motivation are the most common. When I stop enjoying my training workouts and not lookforward to racing is the biggest sign of overtraining for me.