Flutter Kick

Lie on your back with your legs long and your lower back on the floor. Place your hands beside you or under your hips to support a stable pelvis.

Alternate your legs up and down with a small range. Keep your knees mostly straight and move only while your back stays down.

Continue alternating at the same speed. Use your lower abs to prevent your torso from rocking or your legs from swinging widely.

Keeping your back down matters more than leg speed. Shorten the kick if your lower-ab tension starts to fade.

Large kicks or a lifting back strain the hip flexors and lower back. Use a small range that your core can control.

Breathe slowly instead of holding your breath. A longer exhale helps you keep lower-ab tension when the exercise gets hard.

Placing your hands under your hips can reduce back lift at first. As you improve, move your hands beside you and keep the same position.