Lie on a medicine ball with your knees bent and your feet flat on the floor. Hold a dumbbell in each hand with an underhand grip (your palms should be facing you), bend your elbows at a 90-degree angle, and bring the weights just above your chest with your arms straightened but not locked.
Then slowly bend your elbows, lowering the dumbbells down and to your sides until your elbows form a 90-degree angle (keep your elbows in line with your shoulders). Raise the weights to the starting position. Repeat for 15 reps.