Muscle adaptive changes in post-polio subjects.

Nineteen post-polio subjects (9 men and 10 women) aged 41-65 years were studied by means of muscle strength measurements (Cybex) of knee extension and muscle biopsies of the vastus lateralis for morphometric, histopathological and enzymatic analyses. Data from a reference group of 10 male subjects, age 42-51 years, are also given. Fourteen of the post-polio subjects had experienced a post-polio syndrome-like drop in function. All had had polio at least 25 years earlier. In nine of the 19 subjects, type I fibers accounted for more than 70% of the total. There was a significant negative correlation between muscle strength and the percentage of type I fibers in women. Large cross-section areas of muscle fibers were found, with an average mean fiber area of 8 microns 2 X 10(3). It is assumed that the large muscle fiber areas are due to an extreme use of the remaining muscle fibers in post-polio subjects with low muscle strength. There were significant negative correlations between muscle strength values and mean fiber area in men. Most subjects had single atrophic fibers; groups of atrophic fibers were less common. Internal nuclei and splitting were seen in about half of the subjects. The activity of citrate synthase was low, but normal for glycolytic enzymes.