You can’t change where your biceps muscle attaches to the bone, but you can make it appear longer by growing the lower portion of your arm and increasing the overall length of the muscle fibers themselves. The “short bicep” look, where a visible gap sits between the muscle belly and the elbow crease, is largely genetic. Your tendon insertion point is fixed. What you can influence is how much muscle fills that space, and recent research points to specific training strategies that do exactly that.
Why Some Biceps Look Short
The biceps brachii attaches at the shoulder on one end and just below the elbow on the other. The length of the tendon connecting the muscle belly to the elbow varies from person to person. A longer tendon means a bigger gap and a “peaked” bicep that looks shorter. A shorter tendon means the muscle belly extends closer to the elbow crease, creating a fuller, longer appearance. You inherited this structure, and no exercise will move the attachment point.
But what sits underneath the biceps matters just as much for how your arm looks. The brachialis, a thick muscle that runs beneath the biceps and is concentrated in the lower half of the upper arm, can dramatically change the appearance of that gap region. Imaging studies show the brachialis is roughly twice as thick near the elbow as it is at the midpoint of the arm. Growing the brachialis effectively pushes the biceps outward and fills in the lower arm, making the bicep appear to extend further down toward the elbow.
Training at Long Muscle Lengths
The most actionable finding in recent exercise science is that training a muscle in its stretched, lengthened position produces more growth than training it in a shortened position. A 2025 meta-analysis pooling eight studies found that resistance training at longer muscle lengths led to greater increases in both muscle size and fascicle length compared to training at shorter muscle lengths. Fascicle length is the functional length of your muscle fibers. When fibers get longer, the muscle belly itself occupies more physical space.
For the biceps, “long muscle length” means the muscle is fully stretched. This happens when your arm is extended behind your body (shoulder extension) or when your elbow is fully straightened under load. The incline dumbbell curl is the classic example: sitting back on a bench with your arms hanging behind your torso places the biceps under a deep stretch at the bottom of every rep. A bench angle of 45 to 60 degrees works well. A 45-degree angle creates a greater stretch on the long head of the biceps, while 60 degrees is slightly less intense but still effective.
The evidence is still mixed on whether this type of training actually adds new contractile units in series along the fiber (a process called sarcomerogenesis) or simply stretches existing structures. Animal studies show chronic elongation can add these units, but confirming this in living humans remains difficult. What is clear is that the muscles get measurably longer and thicker when trained in stretched positions, regardless of the exact cellular mechanism.
Preacher Curls for the Lower Bicep
If your goal is to fill in the space near your elbow, preacher curls are the most targeted exercise. A direct comparison of preacher curls versus incline curls found that preacher curls produced significantly greater growth in the distal (lower) portion of the elbow flexors, with a mean difference of 0.10 cm more thickness near the elbow. That may sound small, but in a muscle group this size, it’s visible.
The reason likely has less to do with the biceps itself and more to do with the brachialis. When you curl with your arm braced on a preacher pad, the exercise loads the elbow flexors at a long muscle length in a way that disproportionately recruits the brachialis. Since the brachialis sits right in the lower arm region you’re trying to fill, growing it creates the appearance of a longer bicep even though the biceps tendon hasn’t moved. Researchers note that the brachialis is the strongest elbow flexor, and preacher-style movements seem to hit it harder than other curl variations.
Emphasize the Eccentric Phase
Lowering a weight slowly under control (the eccentric phase) places more mechanical tension on the muscle at longer lengths, which is where the stretch-mediated growth signal is strongest. You don’t need a complicated program to take advantage of this. A straightforward approach: lower the weight over about 2 to 3 seconds on every rep of your curls, especially at the bottom portion where the biceps is most stretched.
A more advanced method is accentuated eccentric loading, where you use a heavier load on the lowering phase than you could lift concentrically. In research protocols, participants used 40% more weight on the eccentric phase compared to the concentric phase. For biceps work, this is easiest with a training partner who helps you curl the weight up while you control a heavier load on the way down. A 2-second lift and 2-second lower is a practical starting tempo.
One caution: the distal biceps tendon is most vulnerable during eccentric loading on a flexed elbow. Injuries typically feel like a sudden, sharp tearing sensation in the front of the elbow. This tends to happen with fatigue, often later in a set when form breaks down. If you’re new to eccentric-focused training, start with a weight you can control cleanly for every rep rather than pushing to failure right away. Build volume gradually over several weeks.
A Practical Exercise Selection
You don’t need a dozen curl variations. Three movements cover the key growth drivers for a longer-looking bicep:
- Incline dumbbell curls (45-degree bench): These stretch the long head of the biceps at the bottom of the rep, promoting fascicle lengthening. Let your arms hang fully at the bottom and avoid cutting the range of motion short. This is your primary lengthened-position exercise for the biceps itself.
- Preacher curls: These load the elbow flexors at long muscle lengths with your arm fixed on the pad, targeting the brachialis and the lower portion of the arm. Use a full range of motion and control the descent.
- Hammer curls or reverse curls: A neutral or pronated grip reduces the biceps brachii’s contribution and forces the brachialis and brachioradialis to do more work. Growing these muscles adds thickness to the lower arm and the outer edge of the bicep region.
Two to three working sets per exercise, two or three times per week, gives you enough volume to drive growth without overloading the elbow tendons. Prioritize full range of motion over heavy weight. A partial curl that stops halfway down eliminates the stretched position where the most relevant growth signal happens.
What You Can and Can’t Change
Your biceps insertion point is permanent. If you have a high insertion with a long tendon, you’ll always have some gap near the elbow, and no amount of training will make your biceps look identical to someone with a low insertion. But the practical difference between a trained and untrained arm with the same genetics is substantial. A thicker brachialis fills in the lower arm. Longer fascicles expand the muscle belly. Greater overall size makes the gap proportionally less noticeable.
The biggest mistake is focusing exclusively on peak contraction exercises like concentration curls, which load the biceps in a shortened position. These build the “peak” of the muscle but do little for the lower region. If a longer-looking bicep is your goal, the priority is reversed: spend most of your curl volume in exercises that challenge the stretched position, and treat shortened-position work as a secondary addition.