Preacher Curl Vs. Bayesian Curl: Which Builds Biceps Best?

Over the past few years, training a muscle at longer lengths for greater muscle growth has been a hot topic among fitness influencers and sports scientists alike.

This theory has been supported in studies on the quads, hamstrings, and calves, where exercises that emphasize the stretched position have produced superior muscle growth.

But what about the most important muscle of all, the biceps? Does training them in an extended (stretched) position lead to bigger arms?

A recent study published in the European Journal of Sport Science put this to the test by comparing the preacher curl vs. Bayesian curl (shoulder flexed & shorter muscle length vs. shoulder extended & longer muscle length) with the goal of seeing if training at longer muscle lengths leads to greater biceps hypertrophy and strength gains.¹

Let’s break it down.

Why Training at Long Muscle Lengths May Lead to More Muscle Growth

Several studies have shown that training at longer muscle lengths stimulates more hypertrophy than training at shorter lengths. Here’s why:²

More Muscle Damage

When you stretch your muscles under a heavy load, they experience more muscle damage compared to when you train them at shorter lengths.

While not the main driver of muscle growth, that damage likely triggers a “repair and grow” process that leads to increased muscle size.

Greater Tension on the Muscle

Active tension happens when muscles contract during an exercise.
Passive tension occurs when muscles stretch. Training at longer muscle lengths creates an even greater passive stretch.

Training at longer muscle lengths combines both and creates an even greater passive stretch, sending stronger growth signals than the tension created when training at short muscle lengths.

Sarcomere Addition (Potential Growth Mechanism)

Muscles grow by increasing either:
- The thickness (more muscle fibers stacked on top of each other).
- The length (more sarcomeres—tiny muscle units—added in series).

Some believe that longer-muscle-length training may promote more sarcomeres in series, leading to increased muscle length and size. However, no one has yet seen this happen in a real-life scenario.

***

The benefits of training at longer muscle lengths have been shown in:

Hamstrings (Seated leg curls > Lying leg curls)³
Quads (Leg extensions with hip flexion > Regular leg extensions)⁴
Calves (Standing calf raises > Seated calf raises)⁵

But does the same apply to biceps curls?

New Study: Preacher Curl vs. Bayesian Curl

Researchers took 15 young, active men and put them through a 10-week biceps strength training program.

Participants & Methods

15 young men (Avg. age: 25.6 years, weight: 77.3 kg, height: 175.1 cm),
10-week resistance training program, training twice per week,
Each participant trained one arm with preacher curls (shorter muscle length) and the other arm with Bayesian curls (longer muscle length)
Both exercises were matched in terms of resistance and training volume to ensure a fair fight.

What Was Measured?

Muscle thickness of the biceps brachii and brachialis (via ultrasound)..
One-rep max (1RM) strength in both exercises.

The Results

Both curls significantly increased muscle thickness and strength. However, there was no clear winner—both exercises performed equally well across all measured areas.

Muscle Growth (Hypertrophy)

Both exercises led to significant biceps and brachialis hypertrophy.
There was no significant difference between preacher and Bayesian curls.

Muscle Growth	Preacher Curl (PREA)	Bayesian Curl (BAYE)
Biceps Brachii	6–7% growth	8–9% growth
Brachialis	10% growth	8% growth

What Does This Mean?

Despite Bayesian curls training the biceps at a longer muscle length, they did not result in greater hypertrophy than preacher curls. Unlike the quads and hamstrings, the biceps may not respond as strongly to lengthened-position training.

Strength Gains

Both groups saw significant strength increases.
Like with muscle growth, there was no significant difference in 1RM strength gains.

Strength Gains	Preacher Curl (PREA)	Bayesian Curl (BAYE)
1RM Increase	+28%	+37%

Although the Bayesian curl arm showed a slightly higher strength increase, the difference wasn’t statistically significant (the result could have happened by random chance).

Why Didn’t Bayesian Curls Outperform Preacher Curls?

While training at longer muscle lengths has been shown to be beneficial for other muscle groups, the biceps might be an exception. Here’s why:

Limited Stretch Potential – Unlike the quads or hamstrings, which stretch significantly across two joints, the biceps may not reach the same extreme stretch.
Biceps vs. Brachialis Activation – Some studies suggest that the brachialis (under the biceps) takes on more work in a lengthened position, possibly reducing biceps-specific hypertrophy.
Force-Length Relationship – The biceps might simply be less sensitive to longer muscle length training than other muscles.

What Does This Mean for Your Biceps Workouts?

Both exercises are equally effective for building biceps size and strength.
If you prefer preacher curls for strict form, keep doing them.
If you enjoy Bayesian curls for a deeper stretch, they’re just as good.
Consider rotating between them. If there is a difference that might take more than 10 weeks to appear, you have the best of both worlds.

Final Rep

Training at longer muscle lengths doesn’t always guarantee more muscle growth—the biceps seem to respond similarly to both methods.
Biceps hypertrophy seems to be uniform—neither curl showed regional differences in muscle growth.
Strength gains were similar, meaning your exercise selection comes down to personal preference rather than one exercise offering a distinct advantage.
So, the preacher vs. Bayesian curl? Call it a tie. 🤝 Both exercises build your biceps effectively, so pick the one that feels best for you.

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