“A curl is a curl” is an outdated maxim misaligned with evidence of different growth outcomes via angle variety. In May 2025, House of Hypertrophy (HoH) added a new study to their ongoing analysis of the best biceps exercises, comparing curls with the arms behind the body with preacher curls.
Takeaways
- Shoulder extended curls seem to maximize upper biceps stimuli.
- Shoulder flexed curls might favor the brachialis and brachioradialis.
- Incorporate various curl angles for complete elbow flexor development.
The study recruited 15 untrained men to perform two biceps exercises: Bayesian cable curls with one arm and preacher curls with the other. (1) Both exercises were matched for resistance profile, peaking at 60 degrees of elbow flexion.
Training occurred twice weekly for 10 weeks, with three to five sets of 8 to 12 reps near failure. The thickness of the biceps and brachialis (arm flexors) was measured separately at multiple regions. This study’s advantage was measuring elbow flexors separately.
Both muscles grew at every measured region during both exercises. The researchers suggested that shoulder extended curls are not superior to shoulder flexed curls, despite other studies’ opposite findings.
“Type two errors occur where we say there’s no difference when there is a real difference,” HoH quoted a paper, “Not significant does not equal no difference. In many cases, it means not enough power.” (2)
Moreover, different setups significantly influence the tension curve or how the muscles are challenged during repetitions.
[Related: 4 Studies to Determine the Best Biceps Exercise]
Shoulder Angle and Length-Tension
The long (outer) biceps head crosses the shoulder joint, so arm extension increases its length. Similarly, a study found that the rectus femoris grew more from leg extensions with the hips extended (leaning back) versus sitting upright. (3)
In a Japanese abstract, incline curls (shoulder extended) showed greater biceps gains at the 20-40% region (below the mid biceps); preacher curls favored the brachialis and brachioradialis (Lower elbow flexors). Other trials show mixed results.
Real-World Implications & Variation
The data reveals nuanced outcomes, suggesting curl variety is a logical approach. A study involving detrained men demonstrates that exercise variety promotes greater growth than using only one exercise. (4) A small trial with trained lifters showed modest size advantages for those using only the Bayesian curls. (5)
The differences in size gains may not warrant tossing away your favorite curls, despite not involving shoulder extension.
Provided you’re training hard and sufficient enough, biceps growth will occur with any curl variation.
—House of Hypertrophy
References
- Attarieh P, Nunes JP, Khani S, Negahdar S, Goli A, Nazarirad H, Nazarirad S, Mojtahedi S, Nosaka K, Soori R. Comparison Between Shoulder Flexed and Extended Positions in Elbow Flexion Resistance Training on Regional Hypertrophy and Maximum Strength: Preacher versus Bayesian Cable Curls. Eur J Sport Sci. 2025 Apr;25(4):e12279. doi: 10.1002/ejsc.12279. PMID: 40082069; PMCID: PMC11906226.
- Speed HD, Andersen MB. What exercise and sport scientists don’t understand. J Sci Med Sport. 2000 Mar;3(1):84-92. doi: 10.1016/s1440-2440(00)80051-1. PMID: 10839232.
- Larsen S, Sandvik Kristiansen B, Swinton PA, Wolf M, Bao Fredriksen A, Nygaard Falch H, van den Tillaar R, Østerås Sandberg N. The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise. J Sports Sci. 2025 Jan;43(2):210-221. doi: 10.1080/02640414.2024.2444713. Epub 2024 Dec 19. PMID: 39699974.
- Costa BDV, Kassiano W, Nunes JP, Kunevaliki G, Castro-E-Souza P, Rodacki A, Cyrino LT, Cyrino ES, Fortes LS. Does Performing Different Resistance Exercises for the Same Muscle Group Induce Non-homogeneous Hypertrophy? Int J Sports Med. 2021 Jul;42(9):803-811. doi: 10.1055/a-1308-3674. Epub 2021 Jan 13. PMID: 33440446.
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