Abstract
Fiber type composition, organization, and distribution are key elements in muscle functioning. These properties can be modified by intrinsic and/or extrinsic factors, such as undernutrition and injuries. Currently, there is no methodology to quantitatively analyze such modifications. On one hand, we propose a fractal approach to determine fiber type organization, using the fractal correlation method in software Fractalyse. On the other hand, we applied the kernel methodology from machine learning to build radial-basis functions for the spatial distribution of fibers (distribution functions), by dividing into square cells a two-dimensional binary image for the spatial distribution of fibers from a muscle fascicle and mounting on each cell a radial-basis function in such a way that the sum of all cell functions creates a smooth version of the fiber histogram on the cell grid. The distribution functions thus created belong in a reproducing kernel Hilbert space which permits us to regard them as vectors and measure distances and angles between them. In the present study, we analyze fiber type organization and distribution in fascicles (F2, F3, F4, and F5) of the extensor digitorum longus muscle (EDLm) from control and undernourished male rats. Fibers were classified according to the ATPase activity in slow, intermediate, and fast. Then, (x, y) coordinates of fibers were used to build binary images and distribution functions for each fiber type and both conditions. The fractal organization analysis showed that fast and intermediate fibers, from both groups, had a fractal organization within the four fascicles, i.e., the fiber assembly is distributed in clusters. We also show that chronic undernutrition altered the organization of fast fibers in the F3, although it still is considered a fractal organization. Distribution function analysis showed that each fiber type (slow, intermediate, and fast) has a unique distribution within the fascicles, in both conditions. However, chronic undernutrition modified the intra-fascicular fiber type distributions, except in the F2. Altogether, these results showed that the methodology herein proposed allows for analyzing fiber type organization and distribution modifications. On the other side, we show that chronic undernutrition alters not only the fiber type composition but also the organization and distribution, which could affect the muscle functioning, and ultimately, its behavior (e.g., locomotion).
Highlights
Nature is ordered at all levels, from microscopic to macroscopic, but when a disaster or disease occurs at any level such order changes
We found practically no studies oriented to investigate the organization of fiber types in skeletal muscles and how natural or pathological conditions can modify it, in the case of the extensor digitorum longus muscle (EDLm), which is composed in four fascicles (F2, F3, F4, and F5) with different fiber composition, metabolism, and size (Balice-Gordon and Thompson, 1988; Kissane et al, 2016; Vázquez-Mendoza et al, 2017)
The data obtained in this study was partially reported in Vázquez-Mendoza et al (2017), where we found that chronic undernutrition reduces the percentage of intermediate fibers in the F4, increases this fiber type in the F5 and reduces the fast fibers in the F3 and F5, compared to control fascicles (Table 1)
Summary
Nature is ordered at all levels, from microscopic (atomic, molecular, and cellular) to macroscopic (individual and population levels), but when a disaster or disease occurs at any level such order changes. We found practically no studies oriented to investigate the organization of fiber types in skeletal muscles and how natural or pathological conditions can modify it, in the case of the extensor digitorum longus muscle (EDLm), which is composed in four fascicles (F2, F3, F4, and F5) with different fiber composition, metabolism, and size (Balice-Gordon and Thompson, 1988; Kissane et al, 2016; Vázquez-Mendoza et al, 2017). This particular muscle participates in the extension of toes (each fascicle extends a single toe, the F2 extends toe 2, the F3 extends toe 3, and so on) and in the dorsiflexion of the ankle in the rat
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