Jumping jacks are an efficient way to increase muscle strength. This is true for muscles used in jumping jacks, such as the calves, hip abductors, core muscles, abs, lower back muscles, and shoulder abductors. This is why jumping jacks are commonly included in high-intensity interval programs. However, unlike traditional abdominal exercises that work all parts of your abdomen, jumping jacks focus on the rectus abdominis muscle. So, you won't get great results unless you specifically target this muscle with your efforts. That's why it's important to learn how to do a proper jump jack. Start by standing up straight with your arms at your side. Inhale as you lift your knees off the floor and swing them forward as far as you can. Keep your knees over your feet until the moment you bring them back to start the jump jack. Try not to bend your legs when doing these exercises. Exhale as you drop your knees back to the starting position. Repeat this cycle for as many jumps as you can. It may take several weeks of practicing these every day before you see any change, but once you do, you'll find that your ab definition has increased significantly. You can use weight training to build muscle and burn fat more efficiently. The more muscle you have, the more calories you will be able to burn at rest, and the more fat you will be able to lose.