Copenhagen Planks (short and long lever) primarily target the hip and groin muscles (also known as the adductors), however, they are a great exercise for the core muscle too.

Position yourself in a side plank position on your right forearm with the side of your left foot resting on the top of an exercise bench, step or chair. The 'lever' is between your hip and your foot. Hold your right leg out straight underneath and not balanced on the step or bench. Your shoulders, hips, and foot should be in a straight line, as you push down with the left foot, feeling the tension in your adductors.

Keep a strong core and your pelvis tilted forward to keep a flat back. If you don't have a step, use a pile of books or the bottom step of a staircase.