Overtraining is when an athlete attempts to do more training than he or she can physically/mentally tolerate. It results in several symptoms
Overreaching is pushing the body beyond its limits for a short period to stimulate a training response. It is also called transient over-training.
Undertraining is not providing the body with enough stimulation for performance to improve by training.
RECAP:
OTS is the rapid onset of a persistent decline in the exercise performance of an athlete that is not corrected when changes are made to the training
Symptoms of overtraining are usually referred to as the overtraining syndrome. Symptoms are usually highly individualized and tough to diagnose:
Chronic muscle soreness
Change in appetite
Reduced immune function
Body weight loss
Sleep disturbances
Irritability, restlessness, excitability, anxiousness
Loss of motivation and vigor
Lack of mental concentration
Feeling of depression
Fatigue