The flexor femoris muscle complex (FFMC) is also known as the hamstring muscle complex or commonly as the "hamstrings." Three muscles comprise this group: the biceps femoris, the semitendinosus, and semimembranosus. The FFMC is one of the most frequent sites of muscle injury. Hamstring injuries are becoming more common secondary to the increase in society's pursuit of high-energy athletic activities and the greater mobility of our active seniors. The biceps femoris is the most commonly injured muscle of the FFMC.