How to Tone arms with a cable single-arm pull-down exercise
The "cable single-arm pull-down" will really improve your biceps. If you want huge biceps, Men's Health will get you there with this arms workout.
Attach a stirrup handle to the cable of a lat pull-down machine. Grab the handle with your right arm so your palm faces left and sit on the seat. Keeping your back straight, pull the handle down to the right side of your chest.
Control the weight back to the starting position. When you have completed the desired number of reps, switch to your left arm and repeat.
Too easy? Try not to rest and simply alternate between your right and left arm until you have finished your sets. This will feel very different to a double-handed pull-down with set rests.