Kettlebell Hammer Curls: How To, How Not To, and Benefits

Kettlebell hammer curls are one of the more interesting of the hammer curl variations. The hammer curl motion stays the same; however, the kettlebell presents some challenges… some positive, some not so positive.

Mike demoing kettlebell hammer curls

Kettlebell hammer curls, as their name suggests, requires the use of a kettlebell instead of a dumbbell or other specially-designed handle for cables or barbells. What makes it so interesting is that the bulk of the weight is beyond the hand and not on either side of it.

Consequently, the grip is now heavily involved in maintaining the position of the kettlebell in space, unlike other hammer curl variations where resistance passes through the closed fist.

Muscles Worked

Kettlebell hammer curls isometrically work the muscles of the forearm, mostly the flexors which are responsible for maintaining grip, as they must stay tightly engaged to keep the kettlebell from falling forward out of the hand.

Biceps, brachioradialis, and brachialis muscles

Because kettlebell hammer curls are still a hammer curl variation, they’ll primarily work brachioradialis muscle, as well as the secondary brachialis and biceps muscles.

In fact, theoretically, a kettlebell will work those muscles more intensely than a dumbbell of the same weight.

Why is this?

To understand it, you must first understand the principles of levers. Levers are simple machines, and the joints in our bodies form levers as they’re acted upon by surrounding muscles that cross them.

Arm depicted as a lever system

A lever “arm” is the segment of the lever that intersects at some point along its length with the fulcrum.

The longer the lever arm beyond its fulcrum, the less mechanical advantage the lever has, meaning more force must be applied to move a load at the other end. Segments of the lever arm are divided into the “effort” arm, and the “resistance” arm.

In the case of a curl, the effort arm is the distance between the fulcrum—the elbow—and the insertion point of the biceps and brachioradialis.

The farther down the arm those tendons insert, the greater the mechanical advantage that person’s upper arm muscles will have. The resistance arm is that portion on opposite the effort arm.

This is how it looks like with a dumbbell:

Short resistance arm holding a dumbbell load

So now, take a kettlebell:

Long resistance arm holding a kettlebell load

When you hold a kettlebell, the weight is now farther away from the insertion point of the biceps and because of that, it magnifies the resistance because it lengthens the resistance arm with no change in length to the effort arm. Same effort arm, longer resistance arm.

Regardless of the weight that’s actually written on the weight, you’ve got to work harder to move a kettlebell than a dumbbell that weighs the same.

We’ll get into advantages and disadvantages in a bit.

How to Do A Proper Kettlebell Hammer Curl

Side angle of kettlebell hammer curls

To do a Kettlebell hammer curl correctly you’ll only need a kettlebell, or two kettlebells if you want to work both arms during the same set.

  1. Select a kettlebell that you can lift with good form and one on which you can maintain a grip through a set.
  2. Grip the kettlebell with a neutral grip, thumb side pointing forward.
  3. You can do kettlebell hammer curls standing or sitting…it doesn’t matter. They’re still kettlebell hammer curls either way.
  4. Now, curl the kettlebell so that the neutral grip is held from bottom to top near your shoulder, and back down again.
  5. The kettlebell must remain perpendicular to the forearm. If it starts to sag forward out of your grip, you must select a lighter weight. It’s got to stay straight out in front of your closed fist.
  6. Curl single-sided, two-arm simultaneous, or alternating. It’s ok to bring the kettlebell across your body if you like, as long as the only body part that moves is the forearm.

Low and behold, the kettlebell hammer curl:

Moving image of kettlebell hammer curls

How NOT to Do an Kettlebell Hammer Curl

Kettlebell hammer curls require excellent form and concentration to do well. Finishing a set without compromising form is tough, mostly because of the temptation to use more weight than the grip can handle for an entire set.

Gripping the kettlebell for hammer curls
The right and wrong ways of gripping the kettlebell
  1. Gripping the kettlebell incorrectly. The crossbar of the kettlebell should run straight through your closed fist, pinkie on one side and thumb on the other. Letting the kettlebell slip forward such that the heel of your hand must support the weight is incorrect form. The kettlebell must be an extension of your forearm.
  2. “Breaking” the wrist. The hand should not be allowed to fall forward. If your kettlebell hammer curls look like you’re pouring a cup of tea, you’re doing them wrong.
  3. Using a kettlebell that’s too heavy. A too-heavy weight is the cause of more incorrect form than probably any other cause. Kettlebell hammer curls are not the exercise to do if you’re trying to curl the most weight you’re able.

Benefits

Select kettlebell hammer curls if your objective is to get your forearms some extra work (if they need it) while also working your upper arms.

Mike's pumped forearm
Forearm pumped after kettlebell hammer curls!

High rep sets of light kettlebell curls encourage greater blood supply because of the demand of that constant grip, and therefore contribute to lean, vascular forearms. This assumes you don’t have a large amount of superficial body fat to lose.

The longer resistance arm will overload the target upper arm muscles more than a dumbbell. (Why not just select a heavier dumbbell to compensate for the shorter resistance arm? Good question.)

Kettlebell hammer curls also offer a potential larger range of motion than dumbbells. The shape of the kettlebell puts the “bell” above your fist at the top of each rep such that it won’t come in contact with your shoulder.

For that reason, you’re able to bring your fist as far as your body allows toward your shoulder.

Select kettlebell hammer curls if you need to work on your grip, isometrically work your forearms and encourage vascularity of your forearms.

Remember that the forearm muscles receive some degree of work with almost every exercise that’s done, other than a few of the isolation leg exercises.

Be very cautious to not overwork the forearms and invite an overuse injury like tennis elbow or golfer’s elbow. Those nagging injuries take a long time to heal correctly and usually require a lay-off to do so.

In summary, there’s not a large advantage to kettlebell hammer curls beyond what dumbbells offer. The isometric demand on the forearms and its associated benefits (grip endurance and vascularity), and the somewhat longer ROM are two reasons to select kettlebell hammer curls.

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Perry Mykleby, ACE CPT

Perry started lifting weights in 1974. He is an ACE-certified personal trainer and fitness writer. He holds a journalism degree from the University of North Texas, where he competed in powerlifting. His final competition was the Texas State Open in December of 1982, but has continued to study and practice muscle strength and hypertrophy. He is a four-decade veteran of the medical device industry.

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