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

Anatomy of the Upper Arm

Before diving into the results, let’s break down the basics of biceps anatomy and how these muscles work during your favourite arm 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 crucial biceps heads let you bend your elbow and rotate your hand into a palm-up position. Depending on arm position and grip, different arm curl exercises may emphasize one muscle head over the other, thereby influencing overall biceps development.

How This Study Was Designed to Target the Long and Short Heads

Now that we know the role of the biceps muscle, the question is: which arm exercises target them best? To answer that, I designed an EMG study to compare how different arm exercises activate the long and short heads of that muscle the best. I recruited a group of men and women with various fitness levels to test five popular biceps exercises you might include in your upper arm 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 for targeting the biceps brachii, our EMG research provides evidence-based insights into their effectiveness on muscle activation. Nevertheless, it's essential to note that other exercises not tested here may yield 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 biceps muscles produce while performing an arm curl exercise, the raw data can vary between individuals. Factors such as muscle size, body fat, and genetics (1) all contribute to the final signal. To make the EMG results easier to interpret, I compared each exercise to a baseline: the dumbbell curl. This helps show which arm exercises activate the biceps more or less relative to this standard and is called normalizing the EMG signal.

Since individuals can differ in their muscle activation patterns, we employed statistical methods to analyze the variation in biceps muscle head activation across participants and determine whether the differences between exercises were meaningful or merely random chance. This approach helps reveal which of the five biceps exercises truly stand out.

The results clearly 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 the variation in activation between participants, highlighting that biceps long and short head activation can differ based on individual factors. Additionally, there was no significant difference in muscle activation in the biceps between the dominant and nondominant arms during these arm curl exercises.

These findings raise an important question: Are these biceps 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 of the arm curl exercises produced fairly similar results for both arms. However, the preacher curl notably showed a tendency to activate the short head more relative to the long head. This finding might be because the preacher curl locks the upper arm in an extended position, placing the long head in a shortened position, thereby forcing the short head to adapt to the higher demand (4).

As for which of these upper arm exercises challenged the biceps the most, only one stood out as statistically significant (Figure 3). The hammer curl consistently showed significantly less activation than the incline curl for both biceps heads. Additionally, it had significantly lower short-head activation when compared to the incline, cable, and preacher curls. However, we know that statistical significance doesn’t always tell the whole story for biceps training; looking at effect size helps complete the picture and understand the practical relevance of the EMG results.

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 consistently showed lower biceps activation than all the other arm exercises, its large effect sizes (defined as any value > 0.65 or < -0.65 (7)) highlight its potential unique role in developing the brachialis and brachioradialis muscles. Focusing more on these muscles may contribute to overall arm thickness, rather than providing maximal direct stimulation to the biceps long and short heads (Figure 4). This could also be useful in a rehabilitation setting where you may need to deload the biceps' long and short heads to aid in recovery.

The hammer curl stands out due to its unique biomechanics, which shift the workload to other arm muscles, such as the brachialis (located under the biceps) and the brachioradialis (in the forearm) (5,6). This is underscored by its large effect sizes, highlighting a clear, practical difference (Figure 4). Despite this, the hammer curl's activation patterns between the long and short heads are similar to those of the other exercises, like the dumbbell, incline, and cable curls, making it still a valuable and versatile option for overall arm and forearm thickness and strength.

Choosing the Best Biceps Exercises for the Long and Short Heads Development

With all this data, what’s the best biceps exercise for developing both the long and short heads? 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 very similar activation levels among themselves. Although the preacher curls may slightly emphasize the short head at the expense of the long head (Figure 5), 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. However, if you do choose to incorporate hammer curls into your routine, be aware that you'll likely need to increase the intensity (e.g., more weight or reps) to achieve similar direct biceps stimulation as the other arm curl exercises.