The best way to strengthen your arms is to focus on moves that use multiple muscles, challenge you in a new way, or target often-neglected areas. For example, working the brachioradialis, a small and frequently ignored muscle in your forearm, “helps make your biceps look bigger and adds definition,” says Pete McCall, the American Council On Exercise’s national exercise scientist. Here are 13 exercises that will fast track your road to strong, defined arms.