Fig. 2.

a, b Dynamic ultrasound assessment of a subacute biceps femoris muscle strain. a Assessment with the muscle at rest shows an ill-defined area of low echogenicity within the muscle (arrows), surrounded by ill-defined areas of increased echogenicity, and it is difficult to affirm the presence of focal fiber disruption. b After concentric contraction of the muscle, ultrasound assessment depicts a well-defined area of lower echogenicity in the same zone, consistent with focal fiber disruption (partial tear)