Muscle injuries are among the most common types of injury that athletes (professional and amateur) and the general population report throughout their lives. Various classifications of muscle injuries have been presented in the literature, but in sports medicine they can be broadly classified as lacerations (when a sharp external body cuts the muscle, e.g. in traumatic accidents), contusions (when an external body strikes the muscle itself, e.g. in contact sports) and muscle strains (when muscle fibers are stretched beyond their capacity, e.g. in explosive sporting action requiring high levels of muscle activation and stretching). Muscle strains are among the most frequently reported injuries in sport, with a wide range of clinical presentations and symptoms reported depending on the severity of the injury itself. Several classifications have been developed over the years (Munich Consensus, ISMuLT classification, British Athletic System, etc.), but as a general rule, a three-grade classification is presented to the patient. Grade I represents the mildest type of injury that can be reported, with a small amount of torn muscle fibers, localized pain and a slight reduction in muscle function. The second grade comprises injuries involving a significant amount of time.