Katie Dunlop is back with this 20-minute HIIT routine that features moves such as star jumps, "elf kicks," and candlesticks (basically planks with single-arm reaches). You'll be doing each move for 40 seconds followed by a 20-second rest, and you'll be doing four rounds total (each round is five minutes long with a one-minute break at the end). Start from 3:00 on this video, complete it all the way through, and repeat three more times. Make sure you watch from the beginning so you understand that you'll be alternating sides for some of the exercises with each new round.