This probably won’t come as a shock to you, but the triceps are comprised of three muscles.

What might surprise you, however, is that you probably aren’t working one of those muscles during most triceps exercises, says Men’s Health Fitness Director B.J. Gaddour.

Related: THE 21-DAY METASHRED—an All-New Body Transformation Program From the Men’s Health Fitness Director 

The long head differs from your other two triceps heads—the lateral and medial—because it attaches to your shoulder blades, and is impacted by the degree of shoulder flexion used during an exercise, he explains.

Read: The more your arms are overhead, the more you target the long head.

And since most guys do triceps exercises at chest level or below, the long head tends to get less work than the lateral or medial heads, says Gaddour.  

So how do you work this “forgotten” triceps muscle? With the exercise shown by Gaddour in the video above. Add it to your routine to complete the triceps trifecta.