Overtraining normally comes with these warning signs (from
Signs of Overtraining):
1. Decreased performance
Slower reaction times, reduced speeds and lowered endurance levels are all common signs of overtraining.
2. Agitation, moodiness, irritability or lack of concentration
Too much exercise and too little rest can wreak havoc on the hormones, cause mood swings and create an inability to concentrate.
3. Excessive fatigue and malaise
A body that never has a chance to fully recover from a previous workout will continue to feel more and more fatigued. Some people describe this feeling as “heavy legs.”
4. Increased perceived effort during normal workouts
Overtraining takes a toll on the body, and workouts that were once a breeze can begin to feel like a grind.
5. Chronic or nagging muscle aches or joint pain
Overused muscles and joints can cause constant aches, which may go unnoticed until the body is given proper rest.
6. More frequent illnesses and upper-respiratory infections
Too much exercise taxes all of the body's systems and makes it more difficult to ward off infections.
7. Insomnia or restless sleep
During sleep the body has time to rest and repair itself. An overtrained body, however, is sometimes unable to slow down and completely relax, making it difficult to recover between workouts.
8. Loss of appetite
Overtraining can cause an increase in hormones such as epinephrine and norepinephrine that tend to inhibit appetite. The physical exhaustion and anxiety that often comes with overtraining can also have the same effect.
9. Chronically elevated heart rate at rest and during exercise
A clear sign of an overworked heart muscle is a chronically elevated heart rate. Also, people who overtrain will often find that it takes longer for their heart rate to return to normal after a workout.
10. Menstrual cycle disturbances in women
Exercising excessively and not consuming enough calories may disrupt a woman's menstrual cycle. While some may experience irregular periods, others will stop menstruating altogether.
Some other pointers that I personally have found:
- You don't recover fully within 24-48 hours from muscle soreness
- Generally lethargic / exhausted
A good rule of thumb: At the end of your workout/excercise you should be able to complete the exact same thing again if you were asked to. This is a good way to prevent overtraining but may not always apply I guess.
Biking is a really fun thing to do, expecially with other people.
Even after about 4 years of lifting and working out....this is still the one thing that makes me laugh my ass off to see. 
