Best Biceps Exercises for the Long and Short Head: An EMG Study

Before diving into the results, let’s break down the basics of biceps anatomy and how these muscles work during your favourite curls. The biceps brachii, commonly called simply the 'biceps,' is a large muscle at the front of the upper arm. It has two parts: the long head, running along the outer arm, and the short head, located on the inner arm. These muscles let you bend your elbow and rotate your hand into a palm-up position. Depending on arm position and grip, different exercises may emphasize one muscle head over the other.

How This Study Was Designed

Now that we know the role of the biceps, the question is:  which exercises target them best? To answer that, I designed a study to compare how different exercises activate the long and short heads of the biceps. I recruited a group of men and women with various fitness levels to test five popular biceps exercises you might include in your workouts. The exercises were chosen based on how they’re believed to activate either the short (inner) or long (outer) head of the biceps:

• Incline Curl: Thought to target the long head.
• Hammer Curl: Believed to work either the long or short head, depending on the source.
• Dumbbell Curl: A classic that supposedly activates both heads equally.
• Preacher Curl: Often said to emphasize the short head.
• Wide-Grip Cable Curl: Claimed to focus on the short head.

While these are popular choices, remember that other exercises not tested here might produce different results.

The Best Biceps Exercises for Long and Short Head: Study Results

Since EMG is similar to a very sensitive voltmeter that measures the electrical signals your muscles produce during exercise, the raw data can vary between individuals. Factors such as muscle size, body fat, and genetics (1) all contribute to the final signal. I compared each exercise to a baseline: the dumbbell curl to make the results easier to interpret. This helps show which exercises activate the biceps more or less relative to this standard and is called normalizing the EMG signal.

Since individuals can differ, we used statistical methods to analyze the variation in muscle activation across participants to determine whether the differences between exercises were meaningful or just random chance. This helps reveal which exercises truly stand out.

The results showed that the hammer curl had the lowest biceps activation for both the long and short heads (Figure 2), regardless of which arm was used. The error bars in the data represent how much activation varied between participants, highlighting that activation can differ based on individual factors. There was no difference in activation in the muscles between the dominant and nondominant arms.

These findings raise an important question: Are these exercise differences significant enough to influence your workout choices? Let’s explore what the data really means for your biceps training.

When comparing how much the short and long heads of the biceps were activated, most exercises produced fairly similar results for both arms. However, the preacher curl stood out a bit more with a tendency to activate the short head more relative to the long head. This might be because the preacher curl locks the upper arm in an extended position, placing the long head in a more shortened position, thereby forcing the short head to adapt (4).

As for which exercises worked the biceps the most, only a few differences in biceps activation stood out as statistically significant (Figure 3). For instance, the hammer curl showed significantly less activation than the incline curl for both biceps heads. It also had significantly lower short-head activation than the incline, cable and preacher curls. However, statistical significance doesn’t tell the whole story; looking at effect size helps complete the picture.

Effect size helps us understand how big or meaningful these differences are in real terms for application in training routine design, beyond just statistical significance. While the hammer curl showed lower biceps activation than all the other exercises, its large effect sizes (defined as any value > 0.65 or < -0.65 (7)) highlight its unique role in training both heads of the biceps (Figure 4).

The hammer curl stands out most likely because of its biomechanics. It shifts the workload to other arm muscles like the brachialis (under the biceps) and the brachioradialis (in the forearm) (5,6). This offloads the biceps, resulting in lower activation but making it a valuable exercise for overall arm thickness and forearm development.

The cable, incline, and preacher curls activate significantly differently from the hammer curl. Large effect sizes highlight these differences. However, the hammer curl's activation patterns between the long and short heads are similar to other exercises, such as the dumbbell, incline, and cable curls. This similarity is shown by the slight difference in effect size between the two heads. However, this still makes it a versatile option for balanced biceps development. So, how should you use these findings to optimize your biceps training? Let’s explore the practical takeaways next.

Choosing the Best Biceps Exercises for Long and Short Head Development

So, what’s the best biceps exercise? The answer isn’t black and white. While the hammer curls revealed significantly lower biceps activation overall, the incline, dumbbell, cable, and preacher curls produced similar activation levels between each other. Interestingly, preacher curls may slightly emphasize the short head at the expense of the long head (Figure 5). Still, the overall activation level in the preacher has a small effect size compared to the other exercises, excluding the hammer curl, so it may be practically irrelevant. But if you still choose to attack your arms with hammer curls instead of the other four, you’ll likely need to ramp up the intensity to get similar results.