Weighted Peterson Step-Up

Set one foot flat on the box and lean your torso forward from the hips so your shin stays close to vertical over your foot, rather than punching your knee out in front of your toes. That forward hinge is what shifts the effort into your hip and hamstring instead of your knee. Drive up through your heel, keeping your trailing leg light -- it should barely brush the top, doing as little of the work as possible. Control the step back down through the same hinge you drove up with, then switch which leg leads to work the other side. The added weight makes that forward lean harder to hold, so keep your chest up even as your torso tips forward.