Efeito do Exercício Físico Resistido como Estratégia Profilática nas Lesões Funcionais e Morfológicas da Artrite Reumatoide no Músculo Sóleo de Ratos

Abstract

Rheumatoid arthritis (RA) is a chronic, progressive inflammatory autoimmune disease that affects the joints and periarticular tissues, including skeletal muscle. Specific medications are used in therapeutic protocols for RA and may cause considerable adverse effects. However, other therapeutic approaches, such as physical exercise applied preventively, have emerged as promising strategies for modulating the inflammatory response and preserving joint and musculoskeletal integrity. Therefore, the present study aimed to analyze the morphofunctional effects of high-intensity resistance exercise (RE) on the soleus muscle of Wistar rats when applied preventively before the induction of RA. Thirty Wistar rats, approximately 12 weeks old and with a mean body weight of 320 g, were allocated into four experimental groups: control group (CG), arthritis group (AG), exercise group (EG), and exercise + arthritis group (EAG). Animals in the exercise groups underwent ladder-climbing resistance exercise, with progressive loading, a progressive number of sets, and a fixed number of repetitions, for nine weeks before RA induction. RA was induced using the Complete Freund's Adjuvant (CFA) model. During the experiment, the following assessments were performed: muscle strength, nociception, joint incapacitation, and motor function. Joint edema and the arthritic index were also evaluated. Euthanasia was performed on the eighth and ninth days following RA induction. The soleus muscle was collected and processed for morphological and morphometric analyses of muscle fibers using Hematoxylin and Eosin staining, as well as for analysis of connective tissue using Picrosirius Red staining. An increase in joint edema and arthritic index, as well as functional impairment, was observed in the AG and EAG, as evidenced by reduced muscle strength, nociception, and motor function, in addition to increased joint incapacitation. Morphological analyses indicated focal alterations in muscle fibers resulting from RA, including disorganization of muscle fascicles, muscle fibers with centrally located nuclei, nuclei surrounded by a basophilic halo, muscle fibers undergoing atrophy and necrosis, and inflammatory infiltrates. However, these alterations were less pronounced in the EAG. In the AG and EAG, muscle spindles with disorganized outer capsules and inflammatory cells within their structures were identified. Regarding the morphometric analyses, reductions in fiber area and major and minor diameters, along with increased muscle fiber density, were identified in the AG and EAG. However, these alterations were less evident in the EAG. An increase in connective tissue was observed in the group with RA, whereas no alteration was observed in the EAG. In conclusion, resistance exercise applied preventively in the context of RA demonstrated limited potential regarding functional parameters; however, it promoted partial attenuation of the muscle morphostructural alterations observed in the experimental model. Further studies using prolonged exercise protocols are required.