Myotendinous Junction: Exercise Protocols Can Positively Influence Their Development in Rats.

Area of Science:

• Muscle physiology
• Connective tissue biology
• Exercise science

Background:

• The myotendinous junction (MTJ) is crucial for force transmission between muscle and tendon.
• Physical exercise is a known stimulus that alters MTJ morphology.
• Understanding MTJ adaptations is vital for injury prevention and rehabilitation.

Purpose of the Study:

• To investigate the morphological and molecular adaptations of the biceps brachii MTJ in rats subjected to varied ladder-based exercise protocols.
• To compare the effects of climbing, overload climbing, and combined protocols on MTJ structure.
• To explore the role of telocytes in MTJ adaptation.

Main Methods:

• Light microscopy and immunofluorescence analysis were employed.
• Adult Wistar rats were divided into sedentary, climbing, overload climbing, and combined groups.
• Morphological changes in sarcomere length, sarcoplasmic structures, extracellular matrix, and telocyte distribution were assessed.

Main Results:

• Exercise protocols induced significant reorganization of cellular and collagenous tissues at the MTJ.
• Specific protocols led to distinct adaptations in sarcomere length and sarcoplasmic invaginations/evaginations.
• The extracellular matrix showed notable increases, particularly in the combined climbing and overload climbing group.
• Telocytes were consistently observed adjacent to the MTJ, forming a network.

Conclusions:

• Different exercise protocols induce distinct morphological adaptations at the MTJ.
• These adaptations involve cellular reorganization, extracellular matrix remodeling, and telocyte network formation.
• The studied protocols provide a valuable model for investigating MTJ remodeling and future molecular analyses.