Lie flat with your back on a mat, knees bent, and hold a medium-weight dumbbell in each hand. Raise the weights above your chest so your arms are fully extended toward the ceiling, elbows unlocked, palms facing forward. Touch the inside ends of the weights. (The closer they are, the more of your triceps you'll work.) Slowly lower the weights, keeping them together, until they reach your chest, then press them back over your chest. Repeat 10 to 12 times.