Hack squats:
Start the exercise with a warming up set – squats without weight. In the second set you may load the machine with the minimum weight.
Position your shoulders and back against the pads. Position your feet at shoulder width, extend your legs, and release the safety handles. Slowly lower the weight by bending your knees until your thighs are approximately at 90 degrees. Reverse the movement by driving into the platform and extending the knees and hips. Repeat for the desired number of repetitions.
Pay attention to your knees. They must stay in the same direction as the feet. Make sure that the knees do not go further than the socks.
Do not raise your hips and heels.
Wear an athletic belt when you work with large weights.
Inhale when you go down and exhale when you go up.
Keep your lower back flat, with natural arching.

Hack squats.