What I am going to present in this article is unlike any training system that I am are of -- it is in complete opposition to what our intuition tells and to what we have been conditioned to think about speed and strength training. If you wish to become faster, I am going to suggest you stop working your legs. If you wish to increase your bench press, I am going to suggest you stop working the chest, shoulders, and triceps. I do not mean just for a week. I am talking about an extended length of time -- on the order of 6-8 weeks. I believe the theory presented here could revolutionize the way athletes train, so please read on -- temporarily forgetting old habits and dogmas -- and let the science presented speak for itself.

Before I dive into theoretical speculation, we must look at the science of muscle fibers a bit.

Muscle Fibers

There are three primary muscle fiber types in humans -- Type I, Type IIA, and Type IIB. Type I are referred to as "slow twitch oxidative", Type IIA are "fast twitch oxidative" and Type IIB are "fast twitch glycolytic" (1). And as their names suggest, each type has very different functional characteristics. Type one fibers are characterized by low force/power/speed production and high endurance, Type IIB by high force/power/speed production and low endurance, while Type IIA fall in between (2, 3, 4). The advantages of a certain fiber composition on performance in various sports is both obvious and well established -- for example, marathon runners have 75% slow twitch fibers, while sprinters and weightlifters have 75% fast twitch (5, 6).

These characteristics are a result, primarily, of the fiber's Myosin Heavy Chain (MHC) composition, with MHC isoforms I, IIa and IIx corresponding with muscle fiber types I, IIA, and IIB, respectively (7) -- A small % of hybrid fibers co-expressing two isoforms also exist (8). Myosin Light Chains have been found to exert an effect on some of these properties, but they are minor, and not as well characterized or understood (9), thus we will be dealing with only the MHC.

MHC

MHC IIx possess a shortening velocity 5-10 times that of MHC I and are also faster than MHC IIa (10, 11, 12). Power production, particularly at high velocities, is higher with IIx than either IIa or I as well (11, 13). Force (strength) production has generally been shown to be greater in MHC IIx than IIa (14, 15), though one study found the opposit (16). Both MHC II types have been consistently shown to be superior to MHC I in all three areas (10-16). So, clearly, it is favorable for speed and strength athletes to posses a high % of MHC II, particularly IIx.

The Theory

MHC composition, and thus athletic potential, is thought to be determined to a great extent by genetics. However, various forms of mechanical and electrical stimulus (or lack thereof) have been shown to alter their expression, and it is this potential for manipulation that is the centerpiece of the system I am proposing. I will start with the two most interesting studies:

In the first study, subjects were put on a 3 month resistance training program, which was then followed by 3 months of detraining. Analysis of of the MHC composition of the vastus lateralis was done before training, after training, and following the detraining period (17).

Training resulted in a decrease in MHC IIx from 10% to 4% and an increase in MHC I from 49% to 51% -- the opposite of what we want as a speed/strength athlete. This fast to slow conversion has been well characterized in the literature -- both with bodybuilding type routines such as this, but also with routines typical of those used by power athletes. We will go into considerably more detail on this in a bit.

What is not as well characterized (and what is exciting) is what happened following the detraining period. At the end of the three months, MHC IIx had risen from 4% to 19%, while MHC I had dropped from 51% to 45%. Remember, MHC IIx started out at only 10% before training. This means a significant overshoot in MHC IIx occurred with detraining. Obviously, this is a speed/strength athletes dream.

In the second study (18), fifteen women were divided into two groups -- the first group (T) had undergone a 20 week resistance training program followed by 32 weeks of detraining prior to the study. The second group (U) was totally untrained. Both groups were subsequently put on a 6 week training program. Fiber type % measurements for T were taken before and after the 20 weeks of training, after the the 32 weeks of detraining, and again after the 6 week training period. For U, measurements were taken before and after the 6 week training program.