If you lie thin, you can make an aerial bike. When doing this exercise, you need to make your legs perpendicular to your stomach, so that its effect is the best. Or you can lie on the bed and put your legs vertically on the wall, which is similar to a handstand. You can stick to 15 minutes, and then slowly increase to stovepipe for half an hour. Then flat support is also a very effective exercise, which can burn calories.