June 26, 2026
There are hundreds of different curl and triceps extension exercises that you can do.
But what's the real difference between them? Which ones will get you the most results right now?
In this newsletter, that's exactly what we'll discuss.
We'll cover what specific muscles are targeted by different variations of arm exercises.
Then, we'll finish with some practical guidance on how to schedule and program your arm training over time.
There are three different muscles that can be biased when you do a curl.
These include:
Biceps
Brachialis
Brachioradialis
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Everyone knows where the biceps are: on the front of your upper arm.
This muscle does most of the work in a curl when your palm is facing up toward the ceiling.
This muscle has two heads: a long head and a short head.
They both converge into the same muscle toward your elbow, but the long head crosses the shoulder at its origin while the short head does not.
In practice, this means that your biceps become stretched as your arm moves behind your body.
For example, the biceps are more stretched during an incline curl compared to a spider curl.
There is some research to suggest that training the biceps at longer muscle lengths can be beneficial for muscle growth. [1]
So, ensuring that some training gets done with the muscle in a more stretched position may be to your advantage.
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The brachialis lies directly beneath the biceps.
You can't "see it" the way you can see your biceps. However, it is still worthwhile to train for aesthetic purposes; giving your arm a fuller look overall.
This is the primary curling muscle when your palm is facing down toward the floor, such as a reverse curl.
This muscle only crosses the elbow, so your shoulder position will not put it in a more or less stretched position.
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The brachioradialis is the last major muscle that contributes to elbow flexion.
The entirety of this muscle, though, is found in your forearm- not your upper arm.
If you trace the bone that runs up your forearm on the side of your thumb (your radius), that is where this muscle lies.
This muscle does most of the work of curling when your palms are facing each other, such as in a hammer curl.
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Of these three muscles, the brachioradialis will get the most attention from your usual compound lifts.
Rows, pull-ups, pulldowns, etc. are almost always done with your arm in this neutral position.
Plus, as we said, the entirety of this muscle lies in the forearm; not the upper arm.
For these reasons, focusing your time on the biceps (palm up curling) and brachialis (palm down curling) is going to give you more juice for your squeeze.
There's much less nuance to discuss when it comes to elbow extension training than there is elbow flexion training.
The triceps are the only real player to discuss here. There are other muscles that contribute but none that will materially change your results by focusing on them.
This muscle has three heads: medial head, lateral head, and a long head.
The long head crosses the shoulder, the other two do not.
As a result, the more overhead your arm is, the more stretched the long head of the triceps becomes.
The medial and lateral heads of the triceps will be stimulated the same no matter what position your shoulder is in.
In one study, training the triceps with your arm in an overhead position (where they are more stretched) was shown to result in more muscle growth than training them with your arm at your side. [2]
So, prioritizing triceps training in the overhead position may be to your advantage; although I would recommend including all arm positions at some point over time.
With my clients: I typically write ~4 week training blocks, progress the training block as they move along the 4 weeks, and then write a new training block once the 4 weeks have concluded.
Assuming you follow a similar structure, you don't need to include every kind of curl and triceps exercise in every training block you do.
Earlier, I mentioned that the brachioradialis gets the most attention from your usual pulling work.
That said, your biceps and brachialis are still getting some stimulus from these exercises. If you're progressing on the exercise, you'll be making progress with these muscles too.
So, if you don't have a dedicated biceps or brachialis isolation exercise in your current training block, you can rest assured the muscles are not being ignored.
The same idea is most certainly true for the triceps.
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With that in mind, my typical recommendation is to include ~1 isolation exercise for curling and for the triceps in any given training block.
As you cycle through training blocks over time, you can cycle through which exercise is selected; therefore giving you a complete stimulus over time.
This approach will be more than sufficient for seeing progress over time without taking time away from any other training focus (such as other lifting, endurance, conditioning, etc.)
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