Ten things to look out for in yourself, your workout partner(s) or someone close to you who works out alot:
Decreased performance. Be on the lookout for slower reaction times, a reduction in speed or lower endurance.
Agitation, moodiness, irritability or lack of concentration. Too much exercise and too little rest can wreak havoc on the hormones and cause mood swings and an inability to concentrate.
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."
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.
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.
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.
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.
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.
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.
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.
Source: American Council on Exercise.