There is Such a Thing As Overtraining, Beware! When IGF-1, MyoD & Myogenin Plummet and MAFbx Gnaws Away Your Muscles, It'll Already be Too Late to Acknowledge

Overtraining is real and it's blocking future and reversing past gains.

I am well aware that somewhere out there in the broscientific spheres of the pseudo-experts on the various bulletin boards of a world people call the Internet statements like "there is no overtraining, just undereating" are not uncommon. And in fact, there is a certain connection between the effects / symptoms we usually associate with overtraining on the one, and the consequences of undereating on the other hand. It's a perfect synergy, if you will - a synergy I have been writing about in the past (suggested read: "The SuppVersity Athletes' Triad Series" | read more), but it's not what the most recent study from the Sao Paulo State University in Brazil is about (Alves Souza. 2014).

Overtraining comes in two forms

If this is not your first visit to the SuppVersity the phrases "sympathetic" and "parasympathetic" overtraining will probably sound vaguely familiar. While the latter is the form of overtraining that develops after weeks of 2-4h of daily cardio-training - usually in the presence of undereating, the former is supposed to occur after heavy lifting sessions and is thus more common in sprint type sports.
In the early phases sympathetic overtraining may feel like being "overstimmed", i.e. similar to the strange agitated weakness caffeine naive individuals may experience after their fourth cup of coffee. That's before a deliberating fatigue will take over, episodes of hypoglycemia during (and after) exercise will occur and your life will start to suck as much as your performance (yes, depression is another symptom of overtraining).

Muscle loss instead of gains

While performance oriented athletes usually pull the emergency break, when the notice that their strength, speed, agility, dexterity and all the other qualities that are relevant for world-class performance decline, Mr. Average Joe and his wife Jane tend to ignore the signs until it's already too late and the hormonal changes, Alvez Souza et al. observed in their latest study have already started to gnaw on their precious muscle mass.

Figure 1: Expression of hyptrophy relevant protein and hormones after 12 weeks of (over-)training, as well as subsequent effects on cross-sectional area (CSA) of plantaris muscle; trained vs. sedentary animals (Alves Souza. 2014)

What you can see in Figure 1 are the consequences of 12 weeks of training, in the course of which, the labrats of the Brazilian researchers were subjected to a 1training program with excessive training
load and insufficient recovery time between bouts using a water jump-exercise model of squatting (Figure 1, right):

"Briefly, rats underwent to consecutive training sessions (5 day/week) that consisted of jumps (repetitions) to the water surface (38 cm deep; approximately 150% of rat body length), carrying an overload strapped to a vest on the animal's chest. Initially, all animals completed a 1-week pretraining (once daily) that consisted of a progressive number of sets (2-4) and repetitions (5-12) with a 30-s rest between each set, and carrying an overload of  50%  body  weight  (BW).  Subsequently,  the  rats  began  the  12-week  training  program,  which consisted of progressive overload corresponding to  60% (1 to 3 week), 65% (4 to 6 week), 70% (7th to 8th week), 80% (9th to 10th week), and 85% (11th to 12th week) of BW." (Alves Souza. 2014)

As Alves Souza et al. point out, they have previously demonstrated that this training protocol is effective in promoting type IIA and IID  fiber  atrophy  in  rat  plantaris  muscle  - as long as it is done in a sane and not the typically Western "more helps more" way that was applied in the study at hand.
References:

• Alves Souza et al. "Resistance Training With Excessive Training Load and Insufficient Recovery Alters Skeletal Muscle Mass-Related Protein Expression." Journal of Strength and Conditioning Research (2014). Publish Ahead of Print