The hack squat encompasses the whole range of motion and knee hinge angle of the Squat. This means that the shoulders, hips, knees, and toes are all included.
This serves to "oil the groove" for the conventional barbell Back Squat by putting your ability to squat as deeply as possible to the test and improving it. It also helps to increase your ability to squat.
The hack squat is performed while seated on a piece of exercise equipment in the gym. Although the hack squat and the leg press have some similarities in appearance, they are not the same exercise and should not be confused for one another.
The leg press is performed by sitting at an angle and pressing a weight plate away from yourself while doing the exercise. The hack squat involves standing on the plate, leaning back onto the pads at an angle, with the weight placed on top of you by positioning yourself under the shoulder pads. Afterward, during the concentric portion of the squat, the weight is moved forward.
To put it another way, the moment you regain your balance and stand up, the weight starts to move away from you. A squat with the assistance of a machine is what this exercise is called.
https://www.youtube.com/watch?v=wnU_0pKuYPo