If you want your arms to look wider from the front, you need more muscle around the upper arm. The biceps brachii is part of that picture, but it is not the only muscle that contributes. The brachialis sits beneath the biceps, while the brachioradialis runs along the forearm. Building the elbow flexors as a whole can add size to your arm, even if the biceps itself is your main focus.
Time to find out the best way for you to train.
Heavy curls versus light curls
In this comparison, heavy curls mean a weight you can lift for about 8 to 12 good reps. Light curls mean a weight you can lift for about 20 to 30 good reps. These are useful examples, not strict rules. The same weight can feel different depending on your experience, technique, and the exercise you are doing.
A systematic review and meta-analysis comparing training loads found that muscle growth was broadly similar across lighter and heavier loads when sets were taken to failure. The heavier training produced greater gains in one-rep maximum strength, which makes sense because practicing with heavy weights is more specific to lifting heavy weights. For muscle growth, the review did not find the same clear advantage for heavy loads.
Direct research on curls supports the idea that both approaches can work. In one eight-week study, young men performed preacher curls three times per week using either a heavy load for 8 to 12 reps or a light load for 30 to 40 reps. Both groups trained to failure. MRI measurements showed similar increases in elbow flexor muscle size in both groups.
A larger, more recent six-week study compared unilateral elbow flexions performed for 8 to 12 reps with those performed for 20 to 30 reps. Participants were untrained, and both groups completed four sets to task failure three times per week. The lighter-load group gained more elbow flexor muscle thickness on average in this study. That result is useful, but it does not prove that light curls always build more muscle. The study lasted six weeks, involved people who had not been resistance training, and measured muscle thickness rather than how wide the biceps looked.
Taken together, the evidence does not support a simple rule that heavy curls are best for size, or that high-rep curls are best for size. Both can build muscle. Heavy curls have a clearer advantage when your goal is to improve your ability to lift heavy. For muscle growth, either can be a sound choice.
How hard should your sets feel?
The load you use matters, but so does how close your set gets to your limit. A set stopped while you could still do many more reps is a different challenge from a set that leaves you with just a few good reps in reserve.
A meta-analysis examining resistance training and muscle growth found a small advantage for sets taken to some form of failure compared with sets stopped earlier. However, it did not find that reaching the point where you cannot complete another rep is clearly better than stopping short of that point. A later meta-regression found that muscle growth tended to improve as sets finished closer to failure, while also warning that the exact relationship is uncertain.
For curls, a practical takeaway is to make your working sets challenging. With a heavy load, that might mean finishing when another one or two clean reps would be difficult. With a lighter load, you may need to perform more reps before you reach the same level of effort. If you stop because the set feels uncomfortable while you could still do plenty of controlled reps, the set may not be as demanding as you think.
You do not have to turn every set into a contest. Repeatedly forcing reps with poor form makes it harder to judge the effort you are putting into the target muscles. It may also make your training less consistent. Aim to bring the set close to your limit while keeping the curl controlled.
Which approach should you choose?
Choose the rep range that lets you train hard and repeat the work consistently. Heavy sets are often efficient because they take fewer reps to feel challenging. They also let you practice handling heavier weights. But if you have to swing your body, move your elbows around, or cut the range of motion to finish your reps, the load may be too heavy for the curl you want to perform.
Light sets can be easier to control, but they take more reps and may create more burning or discomfort near the end. That sensation is not proof that the set will produce more growth. The useful part is performing enough challenging work to stimulate the muscles, then recovering well enough to train again.
You can use both approaches across your training. For example, you might perform one curl variation for 8 to 12 reps and another for 15 to 25 reps. That gives you practice with different loads and lets you choose exercises that feel good for your elbows and wrists. There is no need to combine the ranges in every workout if that makes the session unnecessarily long.
The direct curl studies do not establish one ideal number of weekly sets for every person. They do show that participants made progress with repeated sessions over several weeks. Start with a manageable amount of curl work, keep a record of your reps and loads, and add reps or weight when you can do so without losing control. If your performance keeps falling or your joints feel irritated, reduce the work or adjust the exercise.
What about curl variations?
Your curl setup may influence which muscles grow most. In a 12-week study, participants trained one arm with incline dumbbell curls and the other with preacher curls. The incline curl produced somewhat greater growth in the biceps brachii, while the preacher curl produced somewhat greater growth in the brachialis and brachioradialis. Total elbow flexor growth was similar between the two exercises.
This was a comparison of exercise positions, not heavy curls versus light curls. It suggests that choosing a curl variation can affect how growth is distributed among the elbow flexors, but it does not show that one exercise will make everyone’s arms look wider. The study also involved untrained adults, so its results may not transfer exactly to experienced lifters.
For a straightforward routine, use a curl you can perform through a comfortable range of motion without swinging, and progress it gradually. If you want variety, change the position of your upper arm or use a different type of resistance. Keep the exercise stable long enough to judge whether your reps or load are improving.
The answer – both can build bigger biceps
Heavy curls with low reps and light curls with high reps can both build muscle when you perform challenging sets consistently. Heavy curls are the stronger choice for improving heavy lifting strength. Light curls can also stimulate growth, but they require more repetitions and may be uncomfortable as you approach the end of a set.
If your goal is wider looking arms, prioritize consistent training and gradual progress. Choose loads that let you control the curl and bring your sets close to your limit. Use a rep range you can stick with, and consider including more than one range if you enjoy the variety. The research does not show that one range reliably creates wider biceps than the other.
Key takeaways
| Goal or question | Practical takeaway |
|---|---|
| Build more arm muscle | Both heavier and lighter curls can work when sets are challenging. |
| Get stronger at heavy lifting | Include heavier curls because strength gains are specific to the loads you practice. |
| Choose a curl load | Use a weight you can lift with control and a comfortable range of motion. |
| Decide how hard to train | Finish challenging sets close to your limit without needing to force every set to failure. |
| Make arms look wider | Build the elbow flexors over time; curl loads cannot change your muscle attachment points. |
| Add variety | Different curl positions may affect individual elbow flexors, while total growth can be similar. |
References
- Fink, J., Kikuchi, N., Yoshida, S., Terada, K. and Nakazato, K. (2016) ‘Impact of high versus low fixed loads and non-linear training loads on muscle hypertrophy, strength and force development’, SpringerPlus, 5, 698.
- Hammert, W.B., Yamada, Y., Sallberg, R.W., Moreno, E.N., Metcalf, E.E., Young, E.W., Kataoka, R. and Loenneke, J.P. (2026) ‘High- and low-load resistance training produce distinct skeletal muscle growth but similar changes in tendon morphology’, Medicine & Science in Sports & Exercise. Published online 22 June.
- Refalo, M.C., Helms, E.R., Trexler, E.T., Hamilton, D.L. and Fyfe, J.J. (2023) ‘Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: a systematic review with meta-analysis’, Sports Medicine, 53(3), pp. 649-665.
- Robinson, Z.P., Pelland, J.C., Remmert, J.F., Refalo, M.C., Jukic, I., Steele, J. and Zourdos, M.C. (2024) ‘Exploring the dose-response relationship between estimated resistance training proximity to failure, strength gain, and muscle hypertrophy: a series of meta-regressions’, Sports Medicine, 54(9), pp. 2209-2231.
- Schoenfeld, B.J., Grgic, J., Ogborn, D. and Krieger, J.W. (2017) ‘Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis’, Journal of Strength and Conditioning Research, 31(12), pp. 3508-3523.
- Takaki, Y., Kiyohara, H., Yasaka, Y., Morita, N., Ogawa, M., Tanimoto, K., Aoki, T., Machida, S. and Iemitsu, M. (2016) ‘Impact of high versus low fixed loads and non-linear training loads on muscle hypertrophy, strength and force development’, SpringerPlus, 5, 698.
