If you’ve picked up any running related literature in the last few years then you’ve probably heard of over training. What is over training? To be entirely honest, there is no clear definition of overtraining. Most sources agree that overtraining is a general fatigue brought on by training too intensely or too long without proper recovery. In other words, you feel like crap when you train too much. The problem with this general definition is that it doesn’t really explain the mechanism. Yes, increasing training volume and intensity add to the stress on the body, but when you get down to it, but the situation is more complex than that. Some signal in the body must relay this information to the brain. While it is still unclear how this works, some recent research with people suffering from chronic fatigue may hold the answer. To fully understand this you need to know something about how the immune system works. Most cells in the body, including muscle cells, produce signaling molecules. When muscle cells contract they will eventually produce a class of these molecules known as the interluekens, which are the cause of inflammation. If sufficient levels of these of these molecules get produced, they can feedback to the brain and decrease the motor drive in the brain. This results in the reduced pace often seen in over training.
So the question is, what can we do to correct this or delay it? The first thing is that over time, the muscles will likely become accustomed to the increased work load and produce less inflammatory markers. That may not help though in the short term. For the athlete looking to squeeze just a little more training out, I would recommend limiting other sources of inflammation. One of the largest sources of inflammation is the GI tract since it more directly interacts with environmental stressors from food. One of the easiest ways to reduce GI inflammation is increasing fiber consumption. Many of the bacteria vital to proper GI function feed on fiber, and increasing the good bacterial populations may reduce systemic inflammation. I think this may be why Scott Jurek had such a great effect when switching to vegetarian diet. Not only did he get a high dose of vitamins and minerals, but he probably optimized his GI bacterial populations. The second major thing is to supplement with live bacteria, or pro-biotics. I prefer kefir, but numerous forms of yogurts have healthy bacteria.
While somewhat speculative, moderate alcohol consumption (1 drink/day women; 2 drinks/day men) has also been shown to reduce inflammation. I suggest that maybe drinking moderately may reduce chances of overtraining, but this has not been tested in the literature.