Start in a plank position, placing your palms on the chair in front of you and your feet out straight behind you (you should be on the balls of your feet). Keep weight on your toes, shoulders above your the wrists, and your core engaged.
Lift your left knee to your chest, then return to your starting position. Do the same with your right knee.
Alternate for 20 reps (10 each side).
Repeat this circuit as many times as you can for seven minutes. If you're looking for a longer workout, rest for one minute, then complete another seven-minute round of exercises.