Tune Up is a deceptive-looking workout that promises to be a walk in the park and turns out to be quite the battle, especially if you do the right thing and bring your knees up to waist height when doing High Knees (and make sure you land on the ball of the foot as you bring your feet down). It works the core, abs and lower body plus your lungs (of course). You think you're taking a little bit of a break when you're on the ground but you will soon know differently.