Sit on the end of a flat bench with a barbell on your thighs. Roll the barbell down to your knees. Place your toes and the balls of your feet on a block or step with your heels touching the floor. Position your feet so they are hip-width apart. Raise your heels as high as possible by extending your ankles as high as you can. Lower your heels by bending your ankles until your calves are stretched. Repeat.