Because we are grounded by gravity and can neither fly nor levitate our legs power everything. We use them to jump, run, walk, stand and fight. The power of punches and how hard we can push, twist and swing requires good leg strength. The Cardio Fire workout works your lower body, recruiting secondary as well as primary muscle groups and tendons to give you more power in your future physical activities. You know what you need to do: EC FTW.
Extra Credit: 1 minute rest between sets.