Begin seated with your legs out in front of you, knees bent, and feet flat on the ground.
With one dumbbell in each hand resting on your thighs, lie back onto the ground. Make sure your back is totally flat, pulling your abs in to press your lower back against the floor. Adjust your feet if needed; you should just be able to touch your heels with the tips of your fingers.
Hold the dumbbells above your chest, creating a 90-degree angle between your upper arm and forearm. Make sure your palms are facing forward (away from your face) and your hands are over your elbow.
Press both dumbbells up, exhaling as you fully extend your arms. Your hands should be directly over your shoulders and core tight.
Keep your left arm straight and stationary and exhale as you lower your right arm back down to your side with control, bending your elbow to form a 90-degree angle. At the bottom of the movement, your upper arm should be straight out from your shoulder, forming a 90-degree angle with your side.
This counts as one rep. Repeat for 10 reps with your right arm, then switch for 10 reps with your left arm.