Warm up with high knees, a deceptively difficult cardio blast made even more challenging by the fact that the rest periods regress with each set. Then it’s on to two circuits that alternate training for the upper and lower body, allowing one area to recover while the other works. Finally, you’ll finish with burpees—possibly the most exhausting body-weight exercise—then jumping jacks, which is your cooldown. Perform the exercises for time rather than reps—this ensures that you can adjust the pace to your own fitness level. (For example, if you can’t do many pushups, we won’t ask you to do, say, 10. Just do as many as you can in 20 seconds.) Try to keep track of how many reps you get on each move so you can track your progress.
Reps: Work for 20 sec.
Run in place, driving with your legs and pumping your arms. Each knee should rise above hip level. Rest 20 seconds after the first set, then 15, then 10.
Stand with feet shoulder width and get up on the balls of your feet. Exhale as you squat down, keeping your heels in the air. Extend arms forward for balance. Inhale as you stand up and rest your heels on the floor.
Plant your hands on the floor just outside shoulder width and extend your legs behind you. Brace your core so your body remains in a straight line. Lower until your chest is about an inch above the floor and then push back up.
Lie on your back on the floor and bend both legs so your heels are close to your butt. Brace your abs and push through your heels to raise your butt into the air. From there, extend one leg so it’s in line with the other and keep your hips raised using only the one foot to support them. Hold 10 seconds and then switch legs and hold another 10.
Place your hands on the base of a chair and walk your legs forward so your body is suspended by the chair. Lower your body toward the floor until your upper arms are parallel to the floor and then push yourself back up.
Stand with feet shoulder-width apart and bend your hips back to squat to the floor. Touch your hands down and then jump your feet back so you end up in the top of a pushup position. Reverse the motion to come back up to standing.