reckonerConcentration curl
Sit down, brace the back of your upper arm against the inside of your thigh, and curl one dumbbell. Your leg does the job a preacher pad does, so there is nothing left to swing and nothing left to borrow.
Elbow on the thigh, no swinging.
- Pattern
- Arm isolation
- Trains
- Biceps
- Kit
- Dumbbell
- Loading
- A weight you choose
- Reckoner prescribes
- 3 sets of 10 to 15 reps at RPE 8
- Progression step
- 1 kg once the top of the range is clean
- Skill
- Simple to learn
- Recovery cost
- Very low
- Not prescribed if you have declared
- Elbow
Muscles worked
How to do it
Sit and set the elbow
Feet wide, lean forward from the hips, and press the back of your upper arm into the inside of your thigh just above the knee. Elbow on the thigh, no swinging, which is the cue on your wrist.
Let the arm hang straight
The dumbbell hangs between your feet with the elbow fully open. Your free hand goes on the other knee for balance and does nothing else.
Curl up and turn the palm towards you
Bring the bell up towards your shoulder, finishing with the palm fully up. The supinated finish is the position that got the most out of the biceps when the grips were compared1.
Lower all the way and pause
Take the bell back down to a straight arm and stop for a moment before the next rep. Bouncing out of the bottom is the only cheat left on this movement, so remove it deliberately.
What goes wrong
Pushing the elbow forward off the thigh
As the set gets hard the elbow slides down the leg and the shoulder starts helping. Press it in and keep it there, and end the set when you cannot.
Bringing it heavy
One arm, no swing, no leg drive and a fixed elbow. The number will be much lower than a standing dumbbell curl and that is the movement working, not you being weak.
Using it as your only curl
Training one limb at a time and training both produced no significant difference in muscle growth across nine pooled studies2, so this is not an upgrade on a two-handed curl. It is a way to make a lighter set count.
How Reckoner progresses this lift
Six weeks of this lift, from 10 kg, run through the real engine. Nothing below was typed in: the prescription, the decision and the sentence beside it all come from the same code that writes your week.
| Week | Prescribed | What it did |
|---|---|---|
| 1 | 3 x 10 at 10 kg | More reps 10 → 11 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 2 | 3 x 11 at 10 kg | More reps 11 → 12 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 3 | 3 x 12 at 10 kg | More reps 12 → 13 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 4 | 3 x 13 at 10 kg | More reps 13 → 14 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. |
| 5 | 3 x 14 at 10 kg | Deload 40% of sets offFive weeks of building, then one week lighter. About 40% of the sets come off. The load holds and your reps stay where you earned them, so you keep the strength and lose the fatigue. |
| 6 | 2 x 14 at 10 kg | More reps 14 → 15 repsYou finished every set at RPE 7, with room left in the range, so the reps climb before the load does. The lighter week is over, so this is back to three sets. |
Real engine output, not an illustration. Every row was produced by running the engine itself when this page was generated.
The full rule, and why the reps move before the load does, is in how Reckoner decides to add weight.
Questions people ask
Do concentration curls give a better peak?
No exercise changes the shape of a muscle, only its size. What this one does is remove every way of cheating a curl, which usually means the reps you count are the reps you did.
How does this compare with a preacher curl?
Same idea, one arm instead of two and your leg instead of a bench. Both are in the same lane in the library, so Reckoner keeps your history together if you move between them.
Should I turn my palm out at the top?
Finish with the palm facing up, yes. The fully supinated grip produced higher biceps excitation than neutral or palms-down grips at the same load1, and this is a movement with the range to let you rotate.
Similar movements
Reckoner eases the load first when this lift stalls, and offers one of these only if it stalls again after that. A lift already as light as your kit goes has no load left to ease, so the offer comes straight away. Each of them has a page.
Sources
- Coratella and colleagues, Sports, 2023. Biceps brachii and brachioradialis excitation in biceps curl exercise: different handgrips, different synergy ten competitive male bodybuilders curling a cable at an eight repetition maximum with supinated, neutral and pronated grips, with biceps brachii excitation in the lifting phase greater with the supinated grip than the neutral by twelve per cent and than the pronated by nineteen, and brachioradialis excitation also greater with the supinated grip than either of the others, and no significant grip differences in the lowering phase
- Kassiano and colleagues, Sports Medicine, 2025. Comparison of muscle growth and dynamic strength adaptations induced by unilateral and bilateral resistance training: a systematic review and meta-analysis nine studies pooled, finding no significant difference in muscle growth between training one limb at a time and training both, and strength gains that follow specificity, bilateral training favoring bilateral tests and unilateral training favoring unilateral ones