Exercise physiology has made me start looking up a shitload of stuff I never thought about before. Anyways:The purpose of this study was to investigate the long-term effects of high intensity resistance training on myosin heavy chain (MHC) isoform composition of single fibres. Muscle biopsies were obtained from the right vastus lateralis of eight bodybuilders (BB) and seven physical education students (PES). Histochemical analyses were used to determine the fibre type distribution and the fibre cross-sectional area. MHC isoform composition of single fibres was determined with protein electrophoresis. The percentage of fibres expressing MHC IIA and MHC I/IIA was larger in BB (P < 0.05), while MHC IIX was completely absent (P < 0.05). In contrast, myofibrilar ATPase histochemistry only revealed a significantly lower percentage of type IIX fibres in BB (P < 0.05). The muscle fibre profile in the vastus lateralis muscle of BB may represent an adaptation based on the mechanical and biochemical demands of the long-term resistance training. I looked up an old study that said this was true and found this one, published THIS YEAR. Fuck? http://www.springerlink.com/content/xm35757073121w4v/ Thoughts? I'm also going to look around for a similar study in olympic weightlifters and powerlifters to see if the results are the same. For olympic lifters it seems especially counter-intuitive. Cliffs: Bodybuilders had NO (or very little) type IIx (the fastest fibers) and a greater amount of type IIa fibers considered to be fast twitch but not as fast as IIx.