October 21, 2025, 3:26 pm | Read time: 6 minutes

A well-defined bicep is the goal of many recreational athletes. But what’s the best way to achieve it? To answer this question, Brazilian researchers from the Universidade Federal Do Rio de Janeiro compared two classic exercises.¹ The bicep curl was pitted against dumbbell rowing. There’s a big difference between the two, as the bicep curl is an isolated exercise targeting only the bicep, while dumbbell rowing is a compound exercise involving multiple muscle groups. Dumbbell rowing works not only the bicep but also the upper back muscles and shoulders. The study’s result is clear: Bicep curls are more effective than dumbbell rows—at least when it comes to the impact on the bicep.

How the Two Exercises Were Compared

Although the study, with only 25 participants, is considered relatively small, its design allows for optimal comparability. All participants trained one arm exclusively with bicep curls and the other arm with dumbbell rowing, performing the same number of repetitions. The study consisted of two parts. In the first part, the muscle circumference was measured and compared after a single training session with trained athletes. In the second part, untrained individuals underwent an eight-week workout. Here’s a detailed look at the study:

Part 1 of the Study: Trained Participants

The study, although relatively small with only 25 participants, had an optimal design for comparability. All participants trained one arm exclusively with bicep curls and the other arm with dumbbell rowing, performing the same number of repetitions. The study consisted of two parts. In the first part, trained athletes had their muscle circumference measured and compared after a single training session. In the second part, untrained individuals underwent an eight-week workout. Here’s what the study looked like in detail:

Part 1 of the Study: Trained Participants

In the first part, trained men completed a single training session where the muscle circumference was measured and compared. The study involved 25 participants, each training one arm with bicep curls and the other with dumbbell rowing, performing the same number of repetitions.

Part 2 of the Study: Untrained Participants

Nineteen untrained individuals underwent an eight-week workout. One arm was trained with bicep curls, and the other with the compound exercise of dumbbell rowing. At the end of the training program, muscle growth was measured and compared.

Bicep Curls vs. Dumbbell Rows: These Are the Results

The study’s first part, despite involving only trained men, showed that after a single training session, the bicep was larger after curls with the dumbbell than after rowing with the dumbbell. The bicep’s thickness near the shoulder was about 19 percent larger, and near the elbow, it was 16 percent larger than before the exercise. The second part of the study confirmed this: After the eight-week training program, bicep curls led to muscle growth of about five percent in the upper bicep area and eleven percent in the lower area for untrained individuals.

However, it should be noted that only trained men were examined in the first part of the study, and only untrained men in the second part. This raises the question of how the individual results would turn out if the groups were mixed.

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How the Study’s Co-Author Interprets the Results for FITBOOK

“Our results suggest that isolation exercises—like the dumbbell curl—can provide a more direct and complete stimulus for certain muscles, such as the elbow flexors. This is because they target the muscle over a greater range of motion and mechanical tension specific to this joint,” explained Prof. Thiago Matta, co-author of the study, in response to a query from FITBOOK. However, the researcher also emphasized that both isolation exercises and compound exercises are generally effective for hypertrophy.

However: “Isolation exercises allow for greater mechanical load throughout the entire movement of the target muscle and reduce the influence of synergistic muscles that take on part of the work in compound exercises. For two-joint muscles like the biceps brachii, this direct tension over the entire length likely explains the greater and more even hypertrophy we observed with the dumbbell curl compared to rowing.”

However, generalizing the study’s findings to other muscles is not possible. “The effects of exercises on regional hypertrophy depend on specific biomechanical properties (range of motion, moment arm, joint angle, muscle length extension), the functional role of the muscle (single or biarticular), and its architectural structure (fiber orientation, pennation angle, tendon attachments),” the researcher emphasized to FITBOOK. “Since these properties vary between muscles and exercises, an exercise that emphasizes a specific region of a muscle may not have this effect on another muscle. Therefore, muscle- and exercise-specific studies are necessary before these results can be applied to other body parts.”

What a Personal Trainer Says About the Study Results

Personal trainer Jörn Giersberg views the study results with nuance. Especially for smaller muscle groups like the biceps, isolated exercises can indeed be more effective: “For a small muscle group like the bicep, I can generally confirm that—at least compared to certain compound exercises like one-arm rowing,” Giersberg said. However, this cannot be universally applied to every exercise: “Chin-ups, for example, engage the bicep significantly more—so the whole thing looks quite different.”

Isolation Exercises Alone Are Not Enough

Giersberg warns against relying solely on isolation exercises:
“Working only with isolation exercises is not enough. Without compound exercises, the foundation is missing.” Especially when it comes to load, isolated exercises quickly reach their limits: “With bicep curls, you can only move relatively light weights—that’s not enough in the long run to achieve real muscle growth.”

Large Muscle Groups Need Compound Exercises

The larger the muscle group, the more important complex exercises become, Giersberg emphasizes.
“For the glutes, legs, back, or chest, you need compound exercises like squats or bench presses because you can work with significantly heavier loads.”
Isolated exercises like dumbbell flys are useful but not sufficient:
“They alone cannot develop the quality of a chest muscle—the basic load is simply missing.”

The Strength of Isolation Exercises Lies in Targeted Load

Nevertheless, Giersberg sees advantages in targeted muscle engagement:
“Isolation exercises are very precise—they target the specific muscle without other muscle groups stepping in to assist.” This allows the muscle to be more thoroughly fatigued and specifically loaded. Yet even here, the same applies: “You won’t achieve your goals in the long run with isolation exercises alone.”