I've seen countless people come into the gym and throw dumbbells around like potato sacks. They act wild, scream and grunt like gorillas in heat, and then spend their rest periods flexing in the mirror. Although these dudes seem hard-core, they're actually putting a lot of energy into something that won't garner results. They must learn to train smarter.
Many people fail to realize that they already train their arms multiple times per week, without ever doing any direct arm work. Every time we do a pressing movement, we use our triceps.
Every time we pull, we use our biceps and forearms. Because our biceps and triceps get a lot of work during compound movements, it's important to limit the number of sets during isolation work. With dedicated arm training, keep the sets low and the intensity high.
An even bigger problem is that most people don't understand anatomy well enough to train their biceps and triceps effectively. So to build big arms, we need to start by using our head.
How Your Arms Work
The major action of the biceps brachii is elbow flexion and forearm rotation. The name—biceps—means that the muscle is made of two heads, a long and a short. These muscle heads have two different origins but come together to form one tendon, which attaches to the radius.
You can feel your biceps working if you put your left and on your right biceps muscle and then rotate your forearm from a pronated (palm down) to a supinated (palm up) position. You can also feel your biceps participate if you put your left hand on your right biceps and flex your elbow.
Your biceps can fatigue easily, and thus relies on your front deltoid and brachioradialis (anterior forearm muscle) for aid. To get the most out of your biceps training, you need movements that include both flexion and supination.
The triceps brachii is named similarly because of its three heads. The triceps is a slightly larger portion of the arm and just as complex as the biceps. The triceps main function is to extend the elbow. To feel your triceps, place your left hand on the back of your right arm and then extend your right arm until it is completely straight. The long and lateral heads of the triceps create the "horseshoe" shape everyone is gunning for. The medial head is a "deep" muscle.
Not all three heads originate at the same place, but they all insert into the elbow. The long head of the triceps originates at the scapula. To isolate it, your elbow must be over your head.
Now that I dropped some knowledge bombs, let's blow those arms up! Do this workout once per week on any day you choose. Generally, I do an abs/arms/forearms day later in the week after I've already worked my larger muscle groups.
This workout provides more than sufficient arm work. Make sure to keep the intensity high and the pace quick. Hit them hard, hit them fast, and watch 'em grow!