Limited strength in the forearms can result in fatigue when lifting weights or while completing many task required by hands, like cooking, yard work and holding power tools. Dumbbell hammer curls will help strengthen your forearms so you can complete everyday task without arms being painfully worn out. Keep the elbows locked and close to your body. 2  Through the whole hammer curl, keep your elbows locked in at your sides. 3  If you find that when you are doing the hammer curl that your elbows are moving forward, lower your weight.