Place feet hip-width apart on the foot plate of a leg-press machine, knees in line with ankles when bent at 90 degrees. Grasp handles, release foot lock and straighten legs, contracting abdominals so spine is naturally curved.

Keeping weight toward heels, bend knees until they're aligned with hips or until you're unable to maintain a naturally curved spine. Use glute and thigh muscles to press plate out and away from you, back to starting position. Repeat for all reps.