Muscle or Fascial System Lesion (Part I): Understanding the Continuum From Micro to Macro From a Clinical Perspective.

Muscle injuries are the most common traumatic events in both team and individual sports, representing a significant cause of time lost from training and competition. Traditionally described as "muscle tears," these injuries have been interpreted almost exclusively from a contractile perspective. However, emerging evidence highlights the critical role of the myoconnective architecture, comprising the intramuscular connective tissue (endomysium, perimysium, and epimysium), aponeuroses, basal lamina, and extracellular matrix, in force transmission, injury susceptibility, and tissue repair. This narrative review integrates anatomical, histological, and biomechanical evidence to describe skeletal muscle as a composite unit in which passive connective structures function synergistically with active contractile elements. Particular attention is given to the role of the myoaponeurotic and myofascial junctions, frequent sites of indirect, stretch-related injuries, and to the elastic properties of aponeurotic and fascial tissues in energy storage and dissipation during locomotion. Understanding how microscopic organization influences macroscopic injury mechanisms reframes muscle injury as a lesion primarily affecting the myoconnective interfaces rather than isolated muscle fibers. This paradigm shift has implications for diagnosis, prognosis, and rehabilitation, emphasizing the need for preventive and therapeutic strategies that target both contractile and connective components. Part II of this series will apply this framework to the medial gastrocnemius lesion ("tennis leg"), illustrating how detailed knowledge of myoconnective anatomy informs clinical decision-making in sports medicine.