Incinerator is a high-impact aerobic workout that will help you get faster and increase your endurance. High Knees means High Knees here (knees coming up to waist height each time) and you need to pump your arms in order to maintain the pace. Remember to land, always, on the ball of the foot so your heels never touch down. The transition from one exercise to the next should be done as fast as possible and reps really count here so go for as high a number as you can.