Stand holding a dumbbell in each hand using a neutral (aka hammer) grip (palms facing in).
Keeping your elbow by your side, exhale as you curl one dumbbell up towards your shoulder until your biceps is fully contracted.
Hold for a count of two and squeeze your biceps.
Inhale as you slowly lower the dumbbell to the starting position.
Repeat with your opposite arm.
Keep alternating your arms.
Comments and tips
You can perform the dumbbell hammer curl with either both arms at once (see video), one arm at a time, or by alternating your arms (as described above). The latter two methods will recruit more muscles in your core for stabilization.
The dumbbell hammer curl targets your brachioradialis, a forearm muscle; it does not target your biceps brachii, which acts as a synergist, along with your brachialis. That is not to say that your biceps and brachialis do not get a great workout!
The reverse curl is another exercise that most people think targets your biceps when in fact it targets your brachioradialis.