Sedfiter Science

If you are someone like me that likes to reach exhaustion every day, then this article might be for you.

Overtraining is a physical, behavioral, and emotional condition that occurs when the volume and intensity of an individual's exercise exceeds their recovery capacity. They cease making progress, and can even begin to lose strength and fitness. Overtraining is a common problem in weight training, but it can also be experienced by runners and other athletes.
We have to first understand the difference between Overtraining and Overreaching. 

• Overreaching is a short-term decline in performance that can be recovered from in several days.

• Overtraining occurs when it takes weeks or months to recover. This is actually an extremely rare occurrence—as long as nutrition and supplementation are adequate.

Overreaching is our friend, if we want to grow up muscles we have to break down those muscle fibers and then have the proper time to recover.
Overtraining at the other side can be a serious barrier to our goals, lets see how to fight it....
There are two types of overtrain, muscular and cns overtrain. (CNS stands for
Central nervous system )

Muscular Overtrain

Basically when we don't let the proper time to our muscles to recover. This problem is easy to overcome.

•  Sleep at least 7-8 hours
• Let muscles group the proper time to recover before training them again around 24-48h
• Maintain a proper nutrition and supplementation

CNS Overtrain

Central nervous system overtraining is a more serius issue. It doesn't just impact the quads, chest, or back, but rather the entire body. Your CNS is responsible for generating muscular contractions in all types of training, so when you stack workout upon workout, eventually it can tire out.

What happens is that the brain respond to mental and body fatigue (in order to give enough resources to our brain) with stress, that basically means cortisol release.

Cortisol, known more formally as hydrocortisone , is a steroid hormone, more specifically a glucocorticoid, produced by the zona fasciculata of the adrenal cortex.It is released in response to stress and a low level of bloodglucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat, protein and carbohydrate metabolism. It also decreases bone formation. Various synthetic forms of cortisol are used to treat a variety of diseases. cit. Wikipedia.

The main problem with cortisol is that it's an hormone that inhibits protein synthesis ( muscle growth ) and others important body functions like the immune system.

Prolonged cortisol secretion (which may be due to chronic stress) results in significant physiological changes, you may want consider talk to a doctor.

For those reasons we feel sore, weak and we can't grow muscles up.

We have to find the right balance between training and rest, to do so, lets analyse some stress signs that we should know:

Stress Warning Signs and Symptoms
Cognitive Symptoms	Emotional Symptoms
Memory problems Inability to concentrate Poor judgment Seeing only the negative Anxious or racing thoughts Constant worrying	Moodiness Irritability or short temper Agitation, inability to relax Feeling overwhelmed Sense of loneliness and isolation Depression or general unhappiness
Physical Symptoms	Behavioral Symptoms
Aches and pains Diarrhea or constipation Nausea, dizziness Chest pain, rapid heartbeat Loss of sex drive Frequent colds	Eating more or less Sleeping too much or too little Isolating yourself from others Procrastinating or neglecting responsibilities Using alcohol, cigarettes, or drugs to relax Nervous habits (e.g. nail biting, pacing)

For more info about stress signs: http://www.helpguide.org/mental/stress_signs.htm
Lets make clear that it's not only the training part that cause CNS overtrain, but also the lifestyle.
Any type of everyday problem can produce stress (financial, bad habits, sentimental etc etc...).

There are a lot of resources on the net to fix those problems, make sure to find a solution before hitting the gym too hard.

A quick solution may be meditation:

This is a good howto on it http://www.wikihow.com/Meditate.