OS_1

Start with hips and knees fully extended. Bar directly overhead in the frontal plane. Shoulders are active.
Retract and elevate the scapula to initiate active shoulders. For external rotation of the shoulder the armpit should be pointed in the same direction the athlete is facing

OS_2 OS_3 OS_4

To initiate squat hips move back and down until hip crease goes below the knee
Bar remains in the frontal plane and shoulders stay active throughout the movement.
Return to starting position