Delayed onset muscle soreness

A sportive young woman presents highly painful muscular soreness 48 hours after intensive physical exercise. A first MRI (Fig. A) of her legs is performed during the acute pain period (axial T1 and STIR weighted sequences), which shows on the STIR weighted sequencea diffuse high signal intensity of the muscles groups of the posterior compartment of the left leg (right side of image). Moderate high signal intensity is also showed in both gastrocnemius of the right leg (left side of image) (on the right on Fig. A). No abnormalities are shown on T1 in both legs.