Quadriceps
Calves, Glutes, Hamstrings, Adductors
Position self on hack squat machine.
Place feet narrow stance (~3 inches apart) on platform, toes slightly out.
Back against pad, shoulders under pads.
Release safeties.
Lower platform by bending knees.
Descend until thighs below parallel.
Keep back against pad.
Push through feet (focus quads) to return.
Repeat.