Lie on your back with your arms extended upward in front of your chest.
Bend your knees, and bring your legs into tabletop position. Ensure your knees are stacked over your hips and your shins are parallel with the floor. This is your starting position.
On an exhale, draw your ribs in and pull your belly button into your spine, engaging your core. Lower your left arm back and down toward the floor alongside your head. At the same time, extend your right knee and hip to lower your right leg straight toward the floor. Ensure that your arm and leg are lowering at the same speed and that you maintain a neutral spine.
On an inhale, raise your left arm and right leg to return to the starting position. This counts as one rep.
Continue on the other side (your right arm and left leg), and alternate.