Instructions
Kneel on floor. Position ankles under fixed bar or pad or have someone hold your ankles. Place your knees on thick dense pad. Kneel upright with hips straight. Bending your elbows, put your hands up in line with your chest, palms facing outward.
Lower body with hips straight, controlling the descent with your hamstrings as low as possible. Only when you can not control it any longer, touch down on the floor, with your hands on either side of your body. Once your hands make contact with the floor, control the remaining descent with the assistance of your arms. Bring your chest close to the floor and rapidly push off with your hands, just enough to assist your hamstrings to raise your body to the upright kneeling position. Repeat.
Tips
This is not an easy exercise so if you need to work on your hamstrings, make sure also incorporate other exercises, like hamstring curls in to your program. This exercise can also be made easier with the assistance of a resistance band looped around the back of a support (like the machine shown) and then put around your waist, helping you spring back to the start position. The stronger the resistance band, the more assistance it will provide.