Flutter Kicks are a core-burning exercise that targets the lower ab muscles as well as the hip flexors. They’re performed while lying on your back and consist of short, rapid up and down leg movements powered by your abdominal region. To begin, place a mat on a level area of ground. Lie with your back and your head resting firmly on the mat, with your legs extended straight out and heels touching the floor. Take your hands and place them palms down under your glutes to raise your hips slightly off the floor. Your lower back should still be touching the mat. Now raise both feet off the mat a few inches, and while keeping your legs straight, lift your right leg up six inches higher than the left leg. Quickly bring it down to its original position just above the floor, and then quickly lift your left leg up and down in the exact same movement. This counts as one Flutter Kick. Do as many as you can until failure. For an extra challenge, raise your head a little up off the floor so you can see what your legs are doing. To avoid straining your back, make sure your lower spine is pressed into the floor and not arching upwards.