Acute responses of eccentric training in the myotendinous junction in Wistar rats: ultrastructural, molecular and functional analysis

Abstract

The interface between muscle tissue and tendon is denominated the myotendinous junction (MTJ), a region that has a high level of plasticity after exercise and is responsible for transmitting contractile force from muscle fibers to the tendon. Eccentric contractions occur when an external load exceeds the force generated by the muscles, which results in active muscle stretching, allowing the dissipation of mechanical energy during the body's deceleration, with low metabolic cost and lower cardiovascular demand. The regions close to the MTJ present a high level of remodeling, and the predominantly eccentric exercises can promote several adaptations in the entire interface. Thus, the objective of the present work will be to describe the morphoquantitative, ultrastructural and molecular characteristics of MTJ in adult rats after an eccentric training protocol. Adult Wistar rats will be randomly divided into 3 groups: Sedentary (S); Concentric (CC), and Eccentric (EC), all groups will be divided into subgroups of 0h, 24h, 3, 7, and 10 days. The protocol will consist of predominantly concentric or eccentric low-intensity training sessions on a motorized treadmill with an ascending (CC) or descending (EC) slope of 16 degrees at a speed of 20 m/min. The triceps brachii muscle samples will be processed for the techniques of Histochemistry, Transmission Electron Microscopy, Immunofluorescence, and qPCR. The morphoquantitative analyzes of the components of the MTJ will be measured using the ImageJ® software. These descriptions will contribute to the understanding of the acute adaptations of eccentric training in the main region of the locomotor system, for the introduction of new effective methods for the prevention of strain injuries.