We love this exercise because it gets the heart rate up, builds muscle in the calves and shin, and improves foot speed. More importantly, there is no equipment required. Just find a low sturdy surface around the house or outside, then put your feet to work.
Stand behind the box with both feet planted on the ground. Step up onto the box with your right foot then follow with the left. Place right foot back onto the ground and follow with left. Repeat sequence starting with left leg. Do these as fast as possible for 30 seconds 8x.