The leg curl, also known as the hamstring curl, is an isolation exercise that targets the hamstring muscles. The exercise involves flexing the lower leg against resistance towards the buttocks. Other exercises that can be used to strengthen the hamstrings are the glute-ham raise and the deadlift.
A quick explanation: The leg-curl machine targets your hamstrings because it requires you to flex your knees—one of the jobs of your hamstrings—against a resistance. … So as leg curls go, it’s a far better choice than the machine version. But here’s the best part: It’s also a great core exercise.