Spider Curls: How to Do Them, What They Hit, and Who Should Skip Them

Spider curls are biceps curls done chest-down on a 45 degree incline bench, with your arms hanging straight toward the floor. The bench pins your torso in place, so swinging, leaning and shoulder shrugging are close to impossible. What is left is the elbow bending under load. That is the whole appeal.

If you have ever noticed that your “heavy” curls are mostly hips and shoulders, this is the fix. This article is part of our complete arm and forearm training guide, and it covers setup, what spider curls really train, and where they fit next to preacher and incline curls. I will also be blunt about two claims you will hear in the gym (short head isolation and a “peak”) that the research does not back.

How do you do spider curls with proper form?

Set an adjustable bench to about 45 degrees and lie with your chest against the pad, so the top of the pad sits just under your chin. Let your arms hang straight down on either side. Pick up the weights with a supinated grip (palms facing forward), which is the grip most often used for biceps work.

Then run the rep:

• Start from a fully straightened elbow, with the weights hanging still.
• Curl up by bending only the elbow. Your upper arms should stay vertical.
• Squeeze briefly at the top without letting the elbows drift back.
• Lower for roughly 2-3 seconds until the arm is straight again.

What muscles do spider curls work?

Spider curls work the elbow flexors, which are three muscles. The biceps brachii is the one you see in the mirror. Underneath and beside it sit the brachialis and the brachioradialis, which also bend the elbow.

Grip changes how the work is shared. In a small study of 10 competitive bodybuilders, a supinated grip produced more biceps brachii activation (by surface EMG) than pronated or neutral grips during the lifting phase, while the neutral and pronated grips pushed more work onto the anterior deltoid (Coratella et al., 2023). EMG measures electrical activity, not growth, so treat it as a clue rather than a verdict. The practical read: palms-up spider curls are the safest bet if you want the biceps brachii to do most of the work. For the forearm side, see our guide to hammer curls and arm thickness.

Do spider curls build a biceps peak or hit the short head?

Short answer: not as far as anyone has shown. Both heads of the biceps cross the elbow, and the research I could find on curls looks at the biceps brachii as a whole, not at one head. No trial I know of demonstrates that any curl grows the short head selectively.

The “peak” is a shape question. It depends largely on the length of your muscle belly and where your tendons attach, and training does not change either. What training can change is how much muscle you carry.

Where in the range of motion do spider curls load the biceps?

With your arms vertical, gravity pulls straight down on the dumbbell. The hardest point is usually when your forearm is horizontal, around the middle of the curl. The load eases as your forearm approaches vertical at the top. This is basic mechanics rather than a measured result, and the exact feel varies with your arm length and bench angle.

This is why “peak contraction” is a slightly misleading label. Spider curls are not a magic top-range exercise. They are a mid-range-heavy movement that starts from a straight elbow with very little load on it. If you want constant tension, cables help. Our article on Bayesian cable curls covers that approach.

Whether to emphasise the stretched or the shortened part of the curl is an open question. Here is what the studies found, because they do not agree:

• Pedrosa et al. (2023): in 19 untrained young women, training only the first half of the dumbbell preacher curl range (0-68 degrees of elbow flexion) produced greater growth at 70% of upper arm length than training only the second half, plus a bigger 1RM gain (Pedrosa et al., 2023).
• Nunes et al. (2020): 35 young adults did cable preacher curls (more load when the biceps is shortened) or barbell preacher curls (more load when stretched). Muscle thickness rose 7% vs 8%, so hypertrophy was similar (Nunes et al., 2020).
• Zabaleta-Korta et al. (2023): 38 recreationally trained women did incline or preacher curls for 9 weeks. Only the 70% region in the preacher group grew significantly, with no significant difference between groups or regions (Zabaleta-Korta et al., 2023).

The studies differ in design, bench angle, muscle regions measured and sample, and most used untrained or recreationally trained participants over 8-10 weeks. A systematic review of range-of-motion research also noted that evidence for the upper limbs is limited and conflicting (Schoenfeld & Grgic, 2020). The cautious takeaway is to train through a full, controlled range of motion most of the time and not to get hung up on one end of it.

Spider curl vs preacher curl vs incline curl

No study has compared spider curls head-to-head with either. What exists is research on shoulder position. Roughly speaking, the spider curl sits close to the preacher end (shoulder flexed, arm in front of the body), while the incline curl sits at the opposite end (shoulder extended, arm behind the body).

A 2026 MRI study had 21 untrained adults train one arm with incline dumbbell curls and the other with preacher dumbbell curls for 12 weeks. Biceps brachii volume rose more after incline training (+22.1% vs +18.9%, Hedges’ g 0.33), while brachialis (+17.1% vs +21.1%) and brachioradialis (+13.5% vs +17.6%) rose more after preacher training. Total elbow flexor growth did not differ (Kobayashi et al., 2026).

A separate 10-week trial in 15 young men matched resistance profiles and compared shoulder-flexed preacher cable curls with shoulder-extended Bayesian cable curls. Muscle thickness and strength gains were similar (Attarieh et al., 2025). Older EMG work on dumbbell curls found that incline and standard curls loaded the biceps across the whole range, while the preacher version produced high activation only over a short range (Oliveira et al., 2009). Those findings were in untrained or young participants and used different set-ups, so none of this is a ruling on spider curls specifically.

Feature	Spider curl	Preacher curl	Incline curl
Body position	Chest-down on a 45 degree bench	Seated, arms on a sloped pad	Seated or reclined, arms behind torso
Shoulder position	Roughly flexed	Flexed	Extended
Momentum	Almost none	Very little	Some, if you rock
Best use	Strict, controlled reps	Same idea, bench required	Stretched biceps at the bottom

For the shoulder-extended side in detail, see incline dumbbell curls. For the pad-supported side, see our guide to preacher curls.

Dumbbell or barbell for spider curls?

Dumbbells let each wrist rotate and each arm work on its own, which evens out a stronger side. A barbell or EZ bar lets you load heavier and is simpler to hand off. Both work. If you are setting the bench up alone, a light EZ bar on the floor is awkward to pick up while lying on the pad, so dumbbells are usually easier. Nothing here is backed by a trial, it is practical coaching.

How to program spider curls

Treat them as an accessory after your rows and pulldowns. Our pull day plan shows where arm work fits.

• Sets and reps: 2-4 hard sets of 8-15 reps.
• Effort: stop with about 1-2 reps left. Use the RIR/RPE calculator if you want a number.
• Frequency: two sessions a week is a reasonable start. Studies in this area typically trained arms two or three times weekly.
• Progression: add a rep or two each week, then add the smallest plate or a heavier dumbbell once you hit the top of the range.

When to stop or see a doctor

Spider curls are low-risk for most healthy lifters, but any exercise can aggravate an elbow or biceps tendon. Stop and get checked by a doctor or physiotherapist if you notice sharp pain at the front of the elbow, a sudden pop with weakness, bruising near the biceps, or pain that has not settled after a few days. This article cannot diagnose anything, and strict form does not make an injured tendon safe to load.

Bottom line

Spider curls are a strict, easy-to-control way to train the elbow flexors. They are not a short-head trick and they will not create a peak. Use a controlled range of motion, choose a load you can lower slowly, and combine them with a stretched-position curl for balance. For the bigger picture on arm volume and exercise selection, go back to the complete arm and forearm guide.