1. This movement is performed with a hack squat machine which can either be flat or inclined to the ground.
2. Sit in the hack squat machine and place your feet on the pad infront of you. If available, place your shoulders on the pads provided. In general,you should place your feet aproximately shoulder width apart at the front of the pad with your toes pointed slightly out. There are many other foot placing variations you can have to target slightly different area of your thighs.
3. Now, unlock the weight or the pad with a switch usually located at your sides. Now lower the weight down by bending at your knees. This is a replica of the squat motion. Go to the point where you are parallel to the ground. You can go lower if you are more experinced. Be sure to go as low as you safely can. After a short pause, slowly press the weight back up again pushing with you heel rather than your toes. Contracting your thighs at the top.
4. Repeat the movement.

This is a great movement training for lowerl thigh developement. This exercise is baically the same as a squat except with more isolation to the lower quadriceps. With no doubt this exercise will aslo strongly target you hamstrings along with your buttocks. This exercise can be very effective for mass gains because heavy poundages can be handled without a high risk for injury. You must remember that you should get a full range of motion in this exercise. Of course you may have to build up to this level. This exercise will aslo give you overall shape and strength gains. One more point.. push once again with your entire foot especially your heel instead of with your toes which will cause injusry to your knees. Good Luck!