Choose the appropriate weight. Sit on the seat of the hack squat machine and lay your back against the rest. Press the entire soles of your feet against the marked section of the machine foot rest at shoulder width. Grab the machine grips with your hands.
From the starting position, move downwards into a squat. In the lowered position your knees are at a 45-90 degree angle depending on your fitness level. Keep your knees firm and do not let them move sideways. Inhale in the starting position andhold your breath while doing the movement to keep your body core fixed.Exhale while returning to the starting position. Do the required number of repetitions.
Avoid sideway rotation of your tiptoes and heels. Keep your knees in the same direction of your toes. Keep your body core firm and pelvis in a neutral position. Do not overestimate your abilities in the lower position and increase the knee angle only depending on your fitness level.
Start with a lighter weight to master the technique well.
These days, Hack squat usually means machine Hack squat as the original version (named after 19th century German-Russian strongman Georg Hackenschmidt) is more often referred to as Barbell Hack Squat.
Most Hack squat machines are built so that you lean backwards in an angle of about 45 degrees (so you are effectively as much lying as you are standing. The moving part of the machine is held by handles on the sides and it is sometimes also being pushed up through padded part on the shoulders.
The pressure on the shoulders is significant and thus persons with shoulder problems may prefer barbell Hack squat over the machine version.
Most athletes will bend their knees up to 90-degree angle between lower and upper legs but you can also try deeper squats with lower weights.