Morphophysiological Aspects of the Muscle Injury Caused by Eccentric Exercise

Abstract Muscle injuries impair function by damaging cells and triggering inflammation. Eccentric exercise is an effective model for studying these injuries as it overstretches muscle fibers and activates inflammatory responses. The aim of the study was to examine morphological, biochemical, and functional adaptations in the muscle after an eccentric exercise injury protocol. Forty male Wistar rats were divided into Control (C, n = 8) and Injury (I, n = 32) groups, split by recovery time. The injury protocol involved 18 sets/5 min on a treadmill at a −16° incline and 16 m/min. Functional assessments measured joint edema and grip strength. For light microscopy, we used Hematoxylin–Eosin and Picrosirius, and for protein analysis, we measured the levels of interleukin-6 (IL-6), IL-10, and tumor necrosis factor-alpha (TNF-α) via ELISA. Results showed Injury groups with reduced body and muscle mass, and grip strength. The PI0H group exhibited elevated TNF-α and IL-6, while PI24H had increased joint edema. The PI7D group showed an increase in connective tissue and joint circumference. In conclusion, the protocol causes an inflammatory response with increase in nuclei density, and in the area of ​​connective tissue associated with functional decline, with regeneration starting with the presence of neutrophils in PI24H and macrophages in PI4D.