If you want bigger hamstrings, you have to work th semimembranosus, semitendinosis, biceps femoris long head and biceps femoris short head. Each part of the hamstring works to flex the knee (such as a leg curl) and hip (such as a deadlift) besides the biceps femoris short head which only flexes the knee. Here are three exercises to fully work your hamstrings: Stiff Leg Deadlifts Seated Leg Curls Glute ham raises | Pfau Fitness