Do you want bigger guns? Of course you do. Here’s the perfect exercise for bigger biceps.

Bayesian curls

Bayesian curls are a cable biceps curl performed facing away from the cable station. During the exercise, you bend forwards slightly as you flex your biceps to get a good full contraction. Then you lean back again as you lower the weight to fully stretch the biceps. This is the opposite movement of what you will intuitively be inclined to do (which is cheating) so the exercise may feel weird at first. With experience you should be able to find a way to do the exercise that matches your body’s natural movement pattern and provides great biceps stimulation during the entire exercise. Here’s how it looks on video.

Why Bayesian curls are the perfect biceps exercise

Here’s why Bayesian curls are the perfect biceps exercise. The primary stimulus for muscle growth is mechanical tension on the muscle. This tension can be either active or passive. The biceps has a rather special length-tension relationship (illustrated below). The biceps can produce the most active tension when it’s quite stretched, like in its anatomical position with your arm extended at your side. Many muscles become a lot weaker when they are stretched, but the biceps becomes much weaker when shortened. The short head of the biceps loses about 80% of its maximum tensile strength when shortened. The long head of the biceps is barely active at all when fully shortened. The other elbow flexors, the brachialis and the brachioradialis, function similarly, losing most of their tensile strength when fully flexed.

The length-tension relationship of the long head of the biceps. The short head and other elbow flexors are very similar. Length and force are normalized to the optimum fascicle length and peak isometric force, respectively. Simply put, flexing the elbow majorly reduces how much tension it can generate.

Passive tension always peaks when a muscle is stretched, especially via eccentric muscle contractions, like when lowering the weight. The titin muscle filament in particular experiences high passive tension during eccentric muscle contractions to a full stretch, as it’s effectively spring-loaded. Titin is not just a force producing myofilament but also a mechanosensor: titin kinase can initiate anabolic signaling. Titin may thus play a key role in stimulating stretch-mediated hypertrophy via passive tension.

Thus, it’s crucial to train the biceps at long lengths. This maximizes both active and passive tension. A study by Sato et al. (2021) found that training the biceps over the bottom 0-50° of elbow flexion – at long lengths – resulted in triple the growth compared to training the biceps over the top 80-130° of elbow flexion – at short lengths. Yet the average gymgoer does exactly the opposite. They train their biceps mostly with dumbbells and barbells, often skimping on the bottom part of the movement altogether.

Even if you train with a full range of motion, traditional dumbbell and barbell curls cannot optimally stimulate the biceps, as they provide no resistance in the bottom position. When performing a biceps curl, the external moment arm is equal to how much your forearm sticks out horizontally. At 90° of flexion, the lever arm of the weight is maximal and you face peak resistance (illustrated below). That’s why the sticking point is at 90°. In the bottom position, the external moment is essentially zero, so you face practically no resistance in the most important position for maximum growth.

During a dumbbell or barbell biceps curl, the external moment arm of the weight (MR) peaks at 90° of elbow flexion, thus creating the sticking point of the movement in this position.

To train the biceps at long lengths, we need to do 2 things. First, we need to keep our elbows at out sides. The biceps is a tri-articulate muscle that crosses not just the elbow but also the shoulder (weakly) and the forearm (radio-ulnar joint). Raising the elbow flexes the shoulder and thereby shortens the biceps, reducing the tension on the biceps.

Second, we need to do exercises that maintain high biceps tension when your arm is straight. Standing dumbbell and barbell curls woefully neglect the biceps in its stretched position. If you do cable curls facing the cable tower, the problem is even worse. The solution is to perform cable curls while facing away from the cable tower, so that you maintain high muscle tension when your arm is straight. If you don’t experience a good stretch in the bottom, take a step forward, further away from the cable tower. If the bottom position is too hard and it’s pulling your arm back, step back closer to the cable tower. Pivoting up to 90° inwards so that your hand stays close to your torso can also help.

You don’t want to completely neglect the fully contracted position, so if you don’t feel a good contraction anymore when your biceps is fully flexed, you can lean forward with your torso to increase the tension at the top. If the cable ever touches your forearm, you definitely need to lean slightly forward. This creates the characteristic Bayesian curl movement during which you perform a ‘waiter’s bow’ as you curl up the weight and you lean back again as you lower the weight for that nice stretch. Technically, this constitutes biomechanical accommodation of the resistance curve.

Common mistakes

• Treating this like a strength exercise. This is a pure, advanced bodybuilding exercise. You need to actively position yourself and move your torso in such a way to induce maximal resistance throughout the full range of motion. Don’t cheat, skimp on the ROM or focus on moving as much weight as possible at the expense of form. Focus on getting a good stretch at the bottom and a good contraction at the top.
• Letting the weight drag your elbow back. If your arm is dragged back so far that it’s in line with the cable, the weight’s moment arm is zero and you have the same problem as with dumbbell and barbell curls. Keep your elbow at your side.
• Letting the cable touch your forearm as you curl up the weight. This means you’re not leaning forward enough during the curl. You want to avoid any position in which your forearm is fully in line with the cable, as that drops the tension on the biceps to near zero.

Conclusion

Powerful peak contractions, sexy stretch, big biceps. Give Bayesian curls a try!