The single leg hammer curl isn't the first exercise that springs to mind when you think about working your biceps and brachioradialis. However, for those seeking to improve their balance and core stability in addition to their arm strength, this one leg hammer curl exercise really is a great movement to perform—on the surface, at least.
Related Exercise: One leg bicep curl
Single leg hammer curl exercise details
- Main Muscles: Biceps brachii, brachialis, brachioradialis
- Secondary Muscles: Forearm extensors, forearm flexors
- Exercise Type: Strength
- Exercise Mechanics: Isolation
- Difficulty Level: Intermediate
- Equipment Needed: Dumbbells
How to do one leg hammer curls
- Hold a pair of dumbbells by your sides.
- Stand nice and tall with a neutral spine.
- Lift one leg up so that the elevated leg creates a 90-degree angle at your hip joint.
- Curl the weights toward your shoulders, then squeeze your biceps as they become maximally contracted.
- Lower the dumbbells back down under control until your elbows are completely extended.
- Switch legs for your next set, and perform 3-4 sets of 8-12 reps in total.
Single leg hammer curl pros and cons
The one leg hammer curl may not be a bodybuilding favorite, but if you're looking to train your arm strength and balance simultaneously, then the exercise is definitely worth trying. Just keep in mind these drawbacks, too, before deciding if it's right for you and your goals.
Pro: Improved balance
While many weight lifters have impressive muscle size from their strength training, few have the necessary balance to perform more complex exercises. However, by doing movement like one leg hammer curls, you won't have to choose between muscle growth and good balance.
This extra core strength and balance will help you to lift more weight in compound exercises, which typically require more stability than isolation drills.
Of course, you could just train your arms with normal exercises like the lying rope hammer curl and then do your balance training separately. Still, it's undeniably time-efficient to train multiple attributes—strength, power, balance—at the same time.
Con: Reduced bicep stimulation
The trade-off for the enhanced balanced that you'll likely develop by doing the single-leg hammer curl is reduced stimulation of the prime movers, which is to say, the biceps, brachialis, and brachioradialis.
As such, if you're training for hypertrophy, then you're probably best off giving this movement a miss and doing something like a one arm hammer curl instead. This is simply because it's hard to lift heavy weights when you're balancing on one leg.
Pro: Greater workout variety
Sometimes regular hammer curls can get boring. So rather than risk skipping a workout due to low motivation, it can often be a good idea to include novel exercises in your training program to keep your weight lifting activities feeling fresh and exciting.
Isolation exercises are typically very robotic and repetitive. This is great from a muscle growth perspective because the simplicity of such exercises really lets you focus on the target areas.
However, by incorporating other muscles into the movement and challenging your balance, you can add an element of fun into your workouts that makes them feel more enjoyable and less like a chore.
Con: Violates the specificity principle
As mentioned, doing hammer curls on one leg is sub-optimal from a hypertrophy perspective because it's hard to focus on lifting heavy weights when you're off balance.
Second, balancing on one leg while you're curling isn't that hard. There are many other balance exercises out there that are far more challenging. As such, the movement is just okay. It's not fantastic at improving your muscle size or balance because it doesn't target either of these goals optimally.
In other words, it violates the specificity principle of exercise. 
You're better off doing standard hammer curls and then doing separate balance training. This way, you can lift heavier weights for your biceps and do exercises that really challenge your core strength.
Conclusion: Are one leg hammer curls a good exercise?
Single leg dumbbell hammer curls are a good exercise in the sense that they work your arm muscles, train your balance to a moderate extent, and also help to burn calories, which can improve your body composition. However, one leg hammer curls are far from optimal because they're not specific to any particular goal.
If you want to work your biceps, then you're much better off doing an exercise where your feet are planted firmly on the floor. This way, you can lift more weight and thus stimulate faster muscle growth.
Similarly, if you want to increase your core strength, then perform exercises that target your abs and major muscle groups.  Hammer curls are meant to target a very specific set of muscles, so it's recommended not to modify them too much.
Ultimately, single leg hammer curls are fine to perform as an addition to your regular arm and balance exercises. Just don't make them your primary activity. Otherwise, you might struggle to reach your goals if they're specific.
- Specificity | physical conditioning. (2021). Encyclopedia Britannica. https://www.britannica.com/topic/specificity-physical-conditioning
- NHS website. (2021, January 4). Balance exercises. Nhs.Uk. https://www.nhs.uk/live-well/exercise/balance-exercises/