Incline Curl vs Preacher Curl: Which Builds Bigger Biceps?

For total elbow flexor size, neither the incline curl nor the preacher curl has a proven edge. In a 12-week MRI trial of 21 untrained adults, total elbow flexor volume rose 17.6% with incline curls and 19.2% with preacher curls, a gap the statistics could not separate from chance.

What did differ was which muscle grew a little more. The biceps brachii favoured the incline curl, while the brachialis and brachioradialis favoured the preacher curl. Below we cover what four trials found, why the differences are small, where the evidence stops, and how to program and log both curls so your own training history does the final judging.

Is the incline curl or the preacher curl better for biceps?

Neither is better for overall arm size on current evidence. The incline curl (shoulder extended, so the biceps starts stretched) and the preacher curl (shoulder flexed, upper arm braced on a pad) both grew the elbow flexors by roughly 17 to 19% in the longest trial. The differences were small shifts between individual muscles.

Kobayashi and colleagues (2026, Journal of Sports Sciences) put it this way in their conclusion:

"These findings indicate small-to-moderate exercise-specific differences in individual elbow flexor hypertrophy, with limited influence of exercise configuration on total elbow flexor growth and regional hypertrophy patterns."

Kobayashi et al., Journal of Sports Sciences, 2026

The elbow flexors are three muscles: the biceps brachii, the brachialis (underneath the biceps) and the brachioradialis (the top of the forearm). A curl trains all three. The question is only how the load is shared between them.

What did the incline vs preacher curl trials find?

Four recent trials are the closest evidence. Two compared the dumbbell versions directly and found small differences. Two compared cable curls with matched resistance profiles and found none. The table summarises each.

Kassiano's group also tested strength with three-repetition-maximum (3RM) tests. The preacher group improved 1.88 kg more on the preacher curl test, and the incline group improved 0.86 kg more on the incline curl test. The authors read this as the specificity principle: you get better at the lift you practise.

How big are the differences between the two curls?

Small. In Kassiano's trial the regional gaps were 0.08 cm (95% confidence interval 0.02 to 0.13 cm) at the proximal site and 0.10 cm (0.04 to 0.15 cm) at the distal site. That is about one millimetre of muscle thickness each way, a gap too small to see in the mirror.

Kobayashi's effect sizes were modest too. Biceps growth favoured incline curls with a Hedges' g of 0.33. Brachialis (g = 0.50) and brachioradialis (g = 0.47) favoured preacher curls. By convention, values around 0.2 are small and around 0.5 are medium, so these are small to medium effects in untrained arms, and the total did not differ (P = 0.134).

The trials also disagree on where the difference sits. Kassiano reported regional shifts along the arm, while Kobayashi found regional patterns "broadly similar" and a difference mainly between muscles. Treat both as hints about emphasis, not a map for targeting an "upper" or "lower" biceps.

Why might the incline and preacher curl grow muscle differently?

The likely reason is muscle length. The biceps brachii crosses the shoulder as well as the elbow, so the incline curl, with the shoulder extended behind the body, starts the biceps in a more stretched position than the preacher curl does. Training at longer muscle lengths is associated with good growth in some muscles.

Kassiano and colleagues (2023, Journal of Strength and Conditioning Research) reviewed 11 range-of-motion studies and concluded that when training at a longer muscle length, some muscles, including the biceps brachii, tend to experience optimal growth. Our full range of motion vs partial reps guide covers that wider idea.

The two cable trials complicate the story. Attarieh and Larsen both set up the arm position as the only difference and held the resistance profile and elbow range of motion constant. Biceps thickness still rose about 6 to 9% in every condition, with no meaningful gap. Our reading, which the trials did not test directly, is that the small differences in the dumbbell trials may come partly from how the load changes across the curl, not shoulder position alone.

The same theme appeared in our guide to the cable vs dumbbell lateral raise: a plausible length-based advantage did not show up clearly when effort and range were matched.

What are the limits of the evidence?

• Untrained or unspecified participants. The Kobayashi, Larsen and Attarieh samples were described as untrained or young adults, and the Kassiano abstract does not state training status. Trained lifters grow more slowly and may respond differently.
• Short blocks. The trials ran 8 to 12 weeks. Nobody knows whether small regional differences persist, widen or fade over years.
• Small samples. The within-person trials had 15 to 24 completers, which limits the power to detect small differences.
• Different measures. Kassiano and the cable trials used ultrasound thickness. Kobayashi used MRI volume. The results are not directly interchangeable.
• Different exercise set-ups. Dumbbell and cable versions load the arm differently, so findings from one do not transfer perfectly to the other.
• Hypertrophy, not performance. None of these trials tested whether either curl changes pulling strength or how an arm looks.

Because trained men are missing from the evidence, a sensible stance is humility. The trials are consistent on the headline (both curls build the elbow flexors), but they cannot settle which curl a trained lifter should favour.

How close to failure should you take incline and preacher curls?

Close, with care. Robinson and colleagues (2024, Sports Medicine) pooled studies in meta-regressions and found that muscle growth tends to improve as sets finish closer to failure, while strength gains were similar across a wide range. The authors called the analysis exploratory, and proximity to failure was estimated rather than measured.

Curls are a reasonable place to push hard because the load is light and technical risk is low. Larsen's trial took sets to momentary failure. End a set when you can no longer complete a rep with the same upper arm position, not when you have to swing the torso to finish it. Our training to failure vs RIR guide covers the trade-offs, and the RPE vs RIR guide shows how to rate sets.

How should you program incline and preacher curls?

Everything below is our reasoning from the trials, not a protocol that was tested. The only trial numbers used are the weekly volumes and rep ranges the studies reported, all in untrained or unspecified participants.

1. Pick one curl per block as your main biceps exercise. Rotate between blocks if you like. The trials give no reason to expect a cost from swapping, and a change can keep your elbows and shoulders comfortable.
2. Use 8 to 12 reps for most sets. Attarieh used 8 to 12RM and Kobayashi used 10 reps at 70% of 1RM. Light isolation work also tolerates higher reps if you can keep the position consistent.
3. Start with 6 to 10 hard weekly sets for the elbow flexors. The trials used about 6 to 8 (Larsen), 6 to 10 (Attarieh) and 10 (Kobayashi) weekly curl sets. Pulling already counts, so check how many sets per muscle group before adding more.
4. Control the stretch. On the incline curl, let the arm hang behind the torso without letting the shoulder roll forward. On the preacher curl, keep the upper arm on the pad and avoid dropping into the bottom of the rep.
5. Progress with double progression. Add reps until every set reaches the top of your range, then add the smallest load you can. See our double progression guide.
6. Change one variable per block. If you swap curls, keep sets, reps and rest similar so any change in your numbers means something.

Curls are an isolation exercise, so they sit after your heavy pulling in most sessions. Our compound vs isolation exercises guide explains where isolation work earns its place.

Which curl should you choose?

Choose the one you can perform with a full, comfortable range, load progressively and keep doing. The trials show no total-size winner, so practical factors decide. These recommendations are our judgement, not trial findings.

If you are chasing a specific muscle, the evidence is thin but points in a direction. Kobayashi's biceps favoured the incline curl and the brachialis and brachioradialis favoured the preacher curl. A block of each would cover both, which is a reasonable approach for a lifter who is not sure.

How do you track incline and preacher curls?

Log them as separate exercises. A 12 kg dumbbell on an incline bench and a 12 kg dumbbell on a preacher pad load the arm differently, so one combined history would give misleading comparisons. Kassiano's strength results make the same point: each group improved most on its own lift.

IronLedger records weight, reps, RPE or RIR and a note on every set, with the weight pre-filled from the target and editable per set. A practical set-up for curls:

• Weight and reps: the load per arm and the reps you completed, aiming for the top of your rep range.
• RPE or RIR: how close each set came to failure, so 12 reps at RIR 3 is not mistaken for 12 reps at RIR 0.
• Notes: the bench angle, the pad height, or "slow lowering". Free text stays with the set in your history.

A curl is not a lift you would test for a one-rep max, and IronLedger's estimated 1RM uses the Epley formula, so treat it as a trend signal only. The more useful view here is the per-lift trend, which shows estimated 1RM and best set for a single lift across every session you have logged. Run a block of each curl, compare the trends, and keep the one that moves.

What mistakes should you avoid with curls?

• Treating four short trials as settled. The evidence supports a preference at most.
• Comparing numbers across curls. Incline and preacher loads are not interchangeable. Compare each curl only to itself.
• Swinging the weight. Momentum from the torso reduces the work the elbow flexors do. Keep the upper arm still on the preacher curl and the shoulder back on the incline curl.
• Changing several things at once. Swap one variable per block so you can tell what helped.
• Stopping far from failure every set. The meta-regression points towards effort mattering for growth.
• Chasing a muscle you cannot see. Regional differences of under a millimetre are not a reason to restructure your arm day.

Keep learning

Related articles

Comparison

Cable vs Dumbbell Lateral Raise: Which Builds More Side Delts?

12 min read

Comparison

Overhead Triceps Extension vs Pushdown: Which Builds More Triceps?

11 min read

Comparison

Full Range of Motion vs Partial Reps: What the Research Shows

14 min read