Adjust the seat so that your legs are slightly bent when your feet are on the platform. Position the balls of your feet on the edge of platform so your heels are hanging off, then extend your legs but not fully out.

Start by driving the balls of your feet forwards as far as possible then steadily lower your heels downward until your calves feel fully stretched. 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 to finish gently.

Avoid using momentum to bounce up the weight and don't rush.