The hack squat single leg is a compound lower body exercise that targets the quadriceps, hamstrings, glutes, and calves. It involves performing a squat on a hack squat machine using one leg at a time, which helps in improving balance and unilateral strength.

1. Position yourself on the hack squat machine with your back against the pad and shoulders under the shoulder pads.
2. Place one foot on the platform, keeping the other leg extended forward.
3. Unlock the safety handles and lower yourself by bending the knee of the working leg.
4. Descend until your thigh is parallel to the platform or as far as your flexibility allows.
5. Press through the heel of your working leg to return to the starting position.
6. Repeat for the desired number of repetitions before switching legs.