Skull Crusher Lie face up on a flat bench or mat with your dumbbells in hand. Begin with your arms straight up in the air, keeping a slight bend in your elbows. Only bending at the elbows, lower the weights down toward the sides of your head. The weights will end up close to your ears. Press the weights back up to starting position. Complete 12 reps. Image Sources: POPSUGAR Photography and Unsplash / Becca Matimba