Lie on your right side with both legs bent and together and your left arm bent in front of your chest, left palm pressing into the floor in front of your right shoulder.
Bend your right arm under your left armpit and grab the outside of your left shoulder with your right hand. Tighten your abs, and exhale, pressing away from the floor, lifting your upper body off the ground with your left arm.
Bend your left elbow and lower your body back to the floor, but only until your right shoulder lightly touches the ground. Press back up. That’s one rep.
Do 10 reps with the left arm, 10 with the right.
Form tip: Don’t ‘rest’ on the floor when you lower back down. Focus on pressing up with the back of your left arm and keep your abdominals engaged the entire time.