One of the best bicep exercises you can do with dumbbells is the concentration curl, using your knee for added support. To do this, sit on a bench and place the ball of your elbow on the outside of your knee. Keep your back straight and isolate your bicep as you curl the dumbbell up toward your shoulder. This position allows for better control and helps target the biceps more effectively. Slow, controlled movements ensure maximum muscle engagement, making this a powerful exercise for building both strength and size in your biceps.