Twenty-one days of low-intensity eccentric training improve morphological characteristics and function of soleus muscles of mdx mice.

Duchene muscular dystrophy (DMD) is caused by the absence of the protein dystrophin, which leads to muscle weakness, progressive degeneration, and eventually death due to respiratory failure. Low-intensity eccentric training (LIET) has been used as a rehabilitation method in skeletal muscles after disuse. Recently, LIET has also been used for rehabilitating dystrophic muscles, but its effects are still unclear. The purpose of this study was to investigate the effects of 21 days of LIET in dystrophic soleus muscle. Thirty-six male mdx mice were randomized into six groups (n = 6/each): mdx sedentary group; mdx training group-3 days; mdx training group-21 days; wild-type sedentary group; wild-type training group-3 days and wild-type training group-21 days. After the training sessions, animals were euthanized, and fragments of soleus muscles were removed for immunofluorescence and histological analyses, and measurements of active force and Ca2+ sensitivity of the contractile apparatus. Muscles of the mdx training group-21 days showed an improvement in morphological characteristics and an increase of active force when compared to the sedentary mdx group. The results show that LIET can improve the functionality of dystrophic soleus muscle in mice.

Effects of eccentric exercise in rehabilitation of phasic and tonic muscles after leg immobilization in rats.

Eccentric exercise is an essential resource for skeletal muscle rehabilitation following muscle disuse however, abnormalities linked to the tissue recuperation require further research. Our aim was analyze the adaptation ability of rehabilitated muscular tissue in rats during different periods of eccentric training after 10 days of limb immobilization. Twenty-seven Wistar rats were divided into six groups: immobilized 10 days, immobilized and eccentric trained for 10 days, immobilized and eccentric trained for 21 days, and three age-matched control groups. After sacrifice, soleus and plantaris muscles were frozen, cut and stained for general histology using hematoxylin and eosin and Gomori trichrome methods and immunohistochemical methods for fiber typing (mATPase, NADH2-TR), for capillaries (CD31) and intermediate filaments (desmin, vimentin) and high resolution microscopy of resin embedded material. Immobilization resulted in more intense morphological alterations in soleus muscles such as formation of target fibers, nuclear centralization, a reduction in the number of type I fibers, diameter of type I, IIA, IIAD fibers, and capillaries. After 10 days of eccentric training, increases in the nuclear centralization and the number of lobulated fibers were observed. This period was insufficient to reestablish the capillary/fiber (C/F) ratio and distribution of fiber types as that observed in the control group. However, 21 days of rehabilitation allowed the reversal of all morphological and quantitative abnormalities. For the plantaris muscles, 10-days of training restored their basic characteristics. Despite the fact that immobilization affected soleus and plantaris muscles, 10 days of eccentric training was insufficient to restore the morphological characteristics of soleus muscles, which was not the case observed in plantaris muscle.