You can't build massive arms without spending time training your triceps. This three-headed muscle group makes up roughly two-thirds of the muscle mass of your upper arms, while the biceps and brachialis make up the remaining one-third of it. The three heads are known as the long, medial and lateral heads. These names depict the size and/or location of each head. Long refers to the longest head of the triceps, while medial and lateral refers to the heads being located on the inside and outside of your upper arms, respectively.

Out of the three heads of the triceps, the long head is the largest. Another significant anatomical detail you should be aware of the long head is that it crosses two joints: elbow and shoulder. The other two heads only cross the elbow joint. All three heads allow you to extend or straighten your elbows. But the long head also allows you to extend or straighten your shoulders.

You can use this anatomical knowledge to your advantage and maximize the recruitment of the long head during your arm workouts. Doing so will allow you to better stimulate this largest part of the triceps. And, that will ultimately result in better muscular growth of the muscle down the line.

The trick is to perform triceps exercises while your shoulders are flexed. By flexing your shoulders, you will be stretching the long head. Following this with elbow-flexion will further stretch the long head to full capacity. The more stretched a muscle becomes, the more it will be able to contribute during an exercise. This biomechanical manipulation technique is known as passive insufficiency.

The best exercise that incorporates this technique is the overhead triceps extension. When performing this movement, you will be working all three heads of your triceps because you are extending your elbows. However, extra emphasis will be placed on the larger long head as a result of the flexed-shoulder position that you are maintaining throughout the entire range of motion of the exercise.

Execution: hold the inside of end end of the dumbbell between your hands in an underhanded grip. Sit on a vertical weight bench with an upright seat no higher than shoulder height when you are seated. Put your feet firmly on the ground with a stance slightly wider than shoulder-width apart. Raise the dumbbell over your head, thus placing your shoulders in a near-fully flexed position. Start with your arms straight. You should feel quite a bit of a stretch in your triceps long head at this point. You can now begin performing the motion by first bending your elbows as much as possible, therefore lowering the dumbbell behind your head. Then, return the dumbbell over your head by extending your elbows. Do 10 to 12 reps per set and a total of three sets of this exercise during your arm workouts.

Variations: it is best to do this exercise in a seated position, because you will place less stress on your back as a result of the back support provided by the upright weight bench. However, should you feel the need to spice things up a bit, you can always do this exercise in a standing position. You just have to make sure not to excessively extend your lower back to avoid injuring your spine. Other variations you can perform include seated or standing overhead triceps extensions using a barbell or a cable pulley, which also provide a slightly different feel for the exercise and can help change up your workouts a bit to avoid boredom. Furthermore, you can do this exercise one arm at a time using a dumbbell or a cable pulley to ensure that the triceps of both arms are being worked equally.