Ultrastructural study of myotendinous junction plasticity: from disuse to exercise

In the musculoskeletal system, the interface between muscle and tendon, called the myotendinous junction, has the key role of transferring the contractile strength from muscular belly to its tendon. At the ultrastructural level, the myotendinous junction is characterized by tendon finger-like processes that penetrate into the muscle mass, amplifying the interaction between tissues. For many years, this anatomical region has been considered a passive interface and researchers’ attention was focused on muscle and tendon as independent structures. On the contrary, the plasticity of the myotendinous junction in response to different physiological or pathological conditions has been revealed and these changes appear at the morphological, structural and functional levels. In this work, the ultrastructural adaptations of the myotendinous junction to different physiological conditions have been described, suggesting possible causes that could control this plasticity. In particular, while muscle atrophy can reduce the contact interface between tissues, training protocols can amplify this area, allowing an improved ability to transfer increased levels of contractile strength. Moreover, given the frequency of muscle injuries at this level, the potential preventive role of exercise is discussed.