What is Overtraining?
Overtraining is defined as excessive frequency, volume, or intensity of training that results in extreme fatigue, illness, or injury (which is often due to a lack of sufficient rest, recovery, and perhaps nutrient intake). To overtrain on a short-term basis is called overreaching. This, however, is often desired by trainees as this causes microtrauma in the body that needs to repair in order to improve. Overreaching can be fairly easily overcome by a few days rest with proper nutrient intake. The problems that arise is when an individual overreaches and does not allow sufficient nutrient intake or recovery time.
The whole basis of periodization or performance training is to overreach on numerous occasions (planned), which can suppress performance, but then the body will adapt and grow stronger, faster, better, etc. during tapering of training. This is also known as the General Adaptation Syndrome, but if there is too much growth stimulus or too-long of growth stimulus, an individual can get injured.
How Long Can it Last?
Overtraining syndrome can last as long as six months, and recovery can then be delayed. For many individuals, overtraining can be caused by doing too much, too soon, or repetitive overuse, but almost all cases can be reversed after proper rest and recovery.
Sympathetic vs. Parasympathetic Syndromes
Scientists believe sympathetic syndrome can occur first which includes increased sympathetic activity at rest such as increased heart rate, disrupted digestion, etc. It is believed that all forms of overtraining will eventually progress to parasympathetic if allowed to.
An example of anaerobic training would be resistance training. Factors that indicate anaerobic overtraining would be a decreased desire to training, or a decreased joy from training. An individual may also begin to feel more jittery than usual during a workout, as if they have an increase in epinephrine. Although having this extra "surge" of adrenaline may sound like a good thing during training, an overtrained individual would see a decrease in performance.
Anaerobic Overtraining Hormonal Markers
Short-term overreaching can cause increased production of testosterone and insulin-like growth factors (IGF-1) which can improve the efficiency of the repair and recovery period, but once an individual reaches their overtrained state of chronic overreaching, their levels of testosterone and IGF-1 can end up back at regular levels decreasing the affinity for proper recovery.
Anaerobic Psychological Factors
Known as the "inverted iceberg" profile, individuals who partake in heavy resistance training programs can result in decreased vigor, motivation and confidence yet heightened levels of tension, depression, anger, fatigue, confusion, anxiety, and irritability as well as impaired concentration.
Generally caused by extreme levels of training frequency, volume, intensity, or a combination of these variables without sufficient rest or recovery. Increased resting heart rates and increased creatine kinase levels (indicating muscle damage) are two of the indicators for aerobic overtraining. Also witnessed is: decreased performance, decreased % body fat, altered blood pressure, increased muscle soreness, decreased muscle glycogen, decreased total testosterone concentration, decreased ratio of total testosterone to cortisol, and increased sympathetic stress response.
A well-designed fitness training program will cause some overreaching in an individual to create enough response for growth and improvement. However, proper rest and recovery, as well as proper nutrient intake need to also be addressed in order for an individual to not reach a state of overtraining.
Baechle, Thomas R. and Earle, Roger W. Essentials of Strength Training and Conditioning Third Edition