Fig. 7.

Specific fiber specimens show that only type IIx fiber has consistent myosin heavy chains content across a variety of type I fiber content muscle biopsies. Muscle sections from each of the specimens across a wide spectrum of type I fiber content shown in Figs. 3 and 6 were subjected to LCM to obtain pure fiber type samples. The hypothesis that type I fibers would have a specific and characteristic myosin heavy and light chain content whether the total number of type I fibers was predominant or in the minority was refuted. This is most clear when the extremes are compared (12% vs. 82% type I fiber content), where type IIx fibers are similar, but type I fibers at the extremes are more variable, although the content of MYH6 and MYH7 is the same. Unlabeled stack colors at the top of each bar represent small amounts of MYH13, MYH14, MYH15, and MYH16.