This is your warm-up, so it's all about getting the muscles activated and the heart rate slightly elevated.
At Level 3, you're going for a brisk walk where you might still be able to chat, but you'd instead focus on your breath.
Level 4 is where you push yourself to walk as fast as possible without breaking into a jog.
Let's dial it back a notch to Level 3 for seven minutes. This is your body's "reset" period.
Back to Level 4 we go. Another seven minutes at your quickest walking pace.
This is the final round of Level 3 for seven minutes. By now, you should be sweating but also basking in the endorphins.