Gravity Drop

Wearing rubber soled shoes for traction (tennis shoes, etc.) stand on a step or stairway as though you were climbing upward. Feet are parallel, and hip-width apart.
With one hand or both, hold onto railing or other object for support.
Edge your feet backward until the heels are off the stairs and your are hanging onto the stair with the balls of your feet.
Make sure feet remain pointed straight ahead. Let the weight of your body drop your heels off the stair.

You will feel a great stretch in your low leg musculature. The key is to keep your hips over your heels and your shoulders in line with them also.

This exercise forces proper loading of all the load joints of the body by physically stacking them one atop the other.