Abstract: Muscle damage is related to indirect/elongation mechanism, direct impact or dysfunction of the supporting connective tissue and is common in athletes. Muscle trauma can lead to changes that may be observed on US and MRI. MRI or US grading of muscle injury can be performed. In clinical practice the classic three-grade system of muscle trauma proved to be insufficient to predict recovery period and complication rate. Last decennium novel grading systems are developed taking into account new pathophysiological insights. This chapter reviews the relevant imaging anatomy, ultrastructure and (patho)physiology of muscle as well as the radiological characteristics of normal and injured muscle as seen on ultrasound and MRI with emphasis on its clinical relevance introducing the novel grading systems.