2. Hamstring Curls
These are the muscles along the back of your thigh. Lie flat on your stomach. Slowly bring your heels as close to your butt as you can, and hold that position. Do three sets of 15. You can also do this exercise standing while you hold onto a chair and lift one leg at a time. If this becomes easy, you can add ankle weights, slowly increasing the weight from 1 to 3 to 5 pounds.