the hamstring is a group of strong muscles and exercises like glute-ham raise that target those muscles while putting lots of pressure on other body parts are not a good choice. when it comes to bigger and stronger muscles, you have to try to isolate them as much as you can to be able to challenge them enough without fatiguing or hurting other body parts. also, in order to build muscle, you do not always have to add more resistance. sometimes all you need is a little bit of instability to awaken the proprioception system of your body(the mechanism which helps you keep your balance). this exercise not only targets the hamstring, but also the glutes, your core, and a little bit your calves as well.