Over training is caused by prolonged periods of intense training without periods of recovery which is usually characterized by illness or injury. At first the overtraining state can be mild, and if the athlete rests, his body recovers fast. Later however it may be more severe, this is when regulatory mechanisms of the body can not return back to normal during the one or two days which many consider a normal recovery time. This often results in exhaustion. If the athlete has not recovered after a few days rest, they may have entered into a level of overtraining that may require 6 to 8 weeks of rest, or longer.
One of the first things that have to be established is how far an athlete can go with his training before we start to breach the overtraining threshold or the point at which its effects begin to occur. Not only do we have to cater for elite athlete's yet junior or amateur athletes also. Obviously the levels at which elite athletes as opposed to juniors train will vary somewhat dramatically. With juniors it is usually a case of variety and trying to make training sessions as enjoyable as possible to ensure motivation levels are maintained. For example, training 4 days a week and doing the same monotonous activities over and over will at first result in improvements however once focus and motivation have ceased, performance will follow. If, however variety inn relation to training various energy systems and muscle groups is incorporated extra training sessions can be incorporated. Yet if these principles are not included anything over 3 training sessions a week for those under the age of 16 can have negative effects and be classed as overtraining.
As this training is in many cases during a time in which rapid growth and development, both through changes in body type and general physical aspects, overtraining can adversely effect these changes irreversibly e.g. damage of growth plates.