MRI of muscle injuries in elite athletes include a large variety of imaging patterns from very subtle signal changes to complete muscle ruptures, from acute muscle strains to exercise-related chronic changes or complications such as myositis ossificans or muscle hernia. A comprehensive overview is provided in a book chapter by Dimmick and colleagues (Dimmick et al. 2013), which is recommended for further reading. When imaging elite athletes there are differences compared to non-athletes. First, we perform imaging that is often not required in non-athletes and some subtle new diagnoses may be seen. On imaging often multiple pathologies are present so we have to really figure out what's clinically relevant. 35 % of all soccer injuries are muscle injuries and they are the most frequent cause for missing a game. They usually occur during the game where the risk is about six times higher compared to the training (Ekstrand Br J Sports Med. 2011). The mechanism in soccer is mostly an indirect mechanism (96%) and only in rare cases a direct injury which are more common in so called collision sports, for instance rugby or American football. Direct blunt forces cause contusion injuries in the direction of the force an often lead to deep hematomas, for instance in the quadriceps muscle group. Indirect m.i. typically occur after eccentric contraction for instance during sprinting or kicking. Typical injury patterns in indirect mechanisms include a muscle fibre disruption accompanied by muscle oedema and hematoma. The location of the injury within the muscle-tendon-bone complex mainly depends on the age. In youth players, the non-fused apophysis is at most risk while in older individuals it is the degenerated tendon. The majority of elite athletes are in the “intermediate” group with a mature skeleton and no degeneration where the weakest link is the myotendinous junction. So, when reading MR imaging in athletes, one should pay a special focus on the myotendinous junction. In soccer players, 92% of m.i. affect the lower extremity. In 37% the hamstrings are involved, in 18% the quadriceps and in 30% the groin. Within these major muscle groups there are specific “high risk” muscles that are most commonly affected: The biceps femoris muscle (86%), Rectus femoris muscles (88%) and the adductors within the groin complex (Ekstrand, Am J Sports Med 2011). In the assessment of m.i. and besides the clinical examination, ultrasound and MRI are used, CT only in cases of bone involvement (fractures) or heterotopic ossifications. A survey among 23 European soccer teams (Ekstrand, Br J Sports Med. 2012) revealed that 58% teams used MRI to examine suspected m.i., 29% used ultrasound, 40% both and 13% used solely the clinical examination. In elite players MRI is the “gold standard”. The main advantages of MRI in the context of m.i. are: (1) Definite exclusion of a severe injury. Especially the accuracy in diagnosing deep lesions is superior in MRI versus ultrasound (Guillodo et al. 2011) (2) Prediction of time to return to play and (3) Precise follow up and monitoring of muscle healing. Fluid sensitive sequences are most efficacious in rendering conspicuous the intramuscular oedema associated with acute muscle injury, in demonstrating muscle fibre discontinuity and tendon injury. Thus, either Dixon or frequency selective fat-saturated proton-density weighted or short-Tau-Inversion-Recovery (STIR) sequences in long and short axis should be used. A T1 weighted TSE sequence may be added to characterize haematomas and identify of muscle atrophy. In some cases, a third sequence in a third orientation may be helpful, e.g. a T2 weighted TSE sagittal sequence. The use of contrast agent is not necessary in m.i. except rare cases of suspected tumours or septic conditions. Muscle fibre tracking with diffusion tensor imaging (DTI) has been used to assess muscle damage and to measure pennation angle. Normal muscle on DTI demonstrates uniformity in bulk directionality and exhibits orderly arrangements. Disturbance of normal arrangement of muscle fibres is demonstrated on DTI after injury. At present, DTI remains an investigation/research tool and does not play a role in the clinical MRI assessment of muscle injury (Dimmick S. et al. 2013).The most commonly used grading systems divide muscle injuries in 4 grades O’Donoghue et al. 1962, Ekstrand et al. 2012). Grade 0: Normal MRI (“functional injury”), grade 1: oedema, grade 2: partial rupture, grade 3: complete tear. It is obvious that this is only a rough grading and that grade 2 injuries comprise a wide range of muscle injuries from tiny fibre discontinuity to subtotal muscle ruptures. However, surgical treatment is only necessary in grade 3 injuries. Grade I muscle strain demonstrates intramuscular signal hyperintensity on fluid sensitive sequences without discernible muscle fibre disruption. The oedema pattern is classically ‘‘feathery’’ in appearance typically around the myotendinous junction. In partial tears (grade 2), disruption of muscle fibres is identified. Oedema and haemorrhage is present within the muscle or at the muscle–tendon junction, often with perifascial extension. Complete tears (grade 3) demonstrate complete discontinuity of muscle fibres, usually with associated tendon fibre discontinuity and an associated haematoma. The “time to return to play” is a complex estimation and many items have to be taken into account. Besides clinical considerations, imaging predictors have shown to correlate with recovery time. First, the grade of muscle injury is correlated, the higher the grade, the longer the injury period. However, a study by Ekstrand (Ekstrand Br J Sports Med. 2012) did not demonstrate significant differences between grade 1 and 2 injuries regarding time to return. One reason might be that –as stated above- the grade 2 injuries comprise a wide range of injuries. Measures of the longitudinal lengths as well as percentage and volume of muscle injury (Connell et al. 2004) in MRI are strong predictors of the time to return to play. It has been suggested that persistence of oedema defines the period of increased vulnerability to develop a re-tear (Fleckenstein et al. 1989). Also the presence of an intramuscular tendon tear may be associated with delayed return to play (Linklater JM, et al Semin Musculoskelet Radiol 2010)In general post exercise oedema demonstrates a ground glass-like, mild degree of signal hyperintensity and often demonstrates a somewhat patchy geographic distribution. This usually resolves within minutes of cessation of activity but may persist to some degree for several hours without symptoms (Fleckenstein et al. 1988). Delayed onset muscle soreness (DOMS) is an indirect muscle injury with reversible structural damage to the muscle at a cellular level resulting in an acute inflammatory response and an increase in intracellular fluid. The differentiation to grade I injuries are made clinically as DOMS typically commence at 1–2 days after the causative activity, is greatest at 24–48 h and gradually resolves over the next 48–72 h. Chronic exertional compartment syndrome is often bilateral and relieved with rest. This entity is due to increased compartment pressure during exercise. In patients with chronic exertional compartment syndrome, signal hyperintensity within the muscle peaks after cessation of exercise, with a delay in return to the signal intensity and water content of a resting state. Muscle hernias may present as focal out-pouching of the muscle through the fascial defect. As this often occurs during muscle contraction, ultrasound with its ability to visualize movement is superior in this situation. Another complication is the development of myositis ossificans or heterotopic ossification, respectively. Typical imaging features can be seen after about 6 weeks and reflects the zonal composition with a peripheral rim of ossification. In T2 or T2* weighted images, this peripheral rim appears hypointens. In this stage the rim is calcified and is best visualised on CT. The ossification then develops towards the centre. This pattern of calcification in myositis ossificans may be differentiated from osteosarcoma which typically demonstrates central ossification, which then develops peripherally.