Place a platform on the ground, in the middle of the bars path. Stand onto the platform with your feet roughly shoulder width apart and place your traps against the bar. Position the balls of your feet on the platform so your heels are hanging off.
Steadily lower your heels downward until your calves feel fully stretched, then drive your heels back up as high as comfortable. You should feel the weight on the inside of the balls of your feet when performing the exercise. Repeat for the desired amount of repetitions then bend your knees slowly until the weights are caught.
Avoid using momentum to bounce up the weight.