The hammer curl is a core training staple that can absolutely blow up your arms—but are you sure you're even doing the exercise correctly?

For this basic gym necessity, you shouldn't settle for anything other than perfect form—especially because it's such a simple, essential movement that should serve as one of the centerpieces of your training plan. Let Men's Health fitness director Ebenezer Samuel, C.S.C.S. and associate fitness editor Brett Williams guide you through the move's subtleties, saving you from the bad habits that are keeping you from unlocking your fitness potential.

Before you grab a set of dumbbells and start pumping out the reps, take note that it's extremely important to pay attention the movement here. You'll miss out on the potential arm gains if your form is sloppy, and if you let your focus move from the brachialis muscle (more on that in a moment).

Tighten Your Whole Body

Eb says: This is a biceps curl, but that doesn't mean your body gets to be in anything close to a lazy position. In order to get the most out of this (or any) curl, you need to make sure you're moving only at the elbow joint. To insure that, we need to tighten any point where we might cheat. So tighten your glutes and abs, then squeeze your shoulder blades tight, too. That'll help you erase most of your possible swinging points.

Grip the Dumbbells Like You Mean It

Eb says: Don't just hold the dumbbells during this curl; actively grip them. Think about really tightening your hands around each dumbbell, holding it tightly. This will grant you more control over the dumbbell, and it'll also help insure that your brachialis drives the motion. Added bonus: You'll strengthen your forearms and gripping muscles, too.

Squeeze At The Top

Eb says: Curl the dumbbell only as high as it'll go without forcing you to shift your elbow forward, but once you get there, the curl isn't done. Once you're in that position, do your best to squeeze your biceps and arm in general. This little act will force a half-second or so of extra time-under-tension at the top, and it's going to help you develop a stronger mind-muscle connection. It'll also help prevent you from swinging.

When in Doubt, Kneel

Eb says: The most common cheat on any curl is the waist-rocking cheat, where you create motion at your hips to initiate the curling motion. The easy fix to that: Get on your knees.

The position will make you that much more conscious of squeezing your glutes and tightening your abs, which instantly limits your ability to create that waist rock, or other cheats (like arching your back, etc.)

Want to master even more exercises? Check out all of our Form Check guides here.