Machine Curl

What the machine curl actually trains

A machine curl is a seated biceps isolation exercise in which the upper arms rest on a fixed pad and you curl a pair of handles from a straight arm to full elbow flexion.

The biceps brachii flexes the elbow and supinates the forearm. The brachialis, lying underneath it, contributes on every rep regardless of grip, and the brachioradialis helps as the load climbs.

The machine's contribution is not a special stimulus. It is the removal of everything that is not curling. Your upper arms are pinned, your torso is supported, your shoulders cannot flex and the load path is decided for you. What remains is elbow flexion, taken as hard as you like.

That last point is the real argument for it. Curls are one of the few exercises where taking a set to genuine failure is trivially safe, and a machine makes it safer and simpler still. There is no dumbbell to lower awkwardly and no bar to peel off your thighs. You pull until nothing moves, then stop.

The cam is the other advantage, at least in theory. A well designed curl machine varies the resistance through the range so the exercise stays hard where you are strong and eases where you are weak, which a dumbbell cannot do. Whether your gym's machine achieves this is a matter of luck, and the way to find out is to do a set and notice where it gets hard.

Two honest limitations. The path and the hand spacing are fixed, so if the machine does not fit you, it does not fit you. And like every pad supported curl, it loads the mid range and the contraction rather than the stretch.

Setting up and executing

Adjust the seat so the pad meets the back of your upper arms and your elbows sit level with the machine's pivot. That alignment is the only setup decision this exercise asks of you, and getting it wrong changes the whole resistance curve.

Sit down and lay both upper arms flat on the pad, with the armpits in contact rather than hovering.

Take a handle in each hand with the palms facing up and set the shoulders down rather than letting them ride towards your ears.

Straighten the elbows to reach the start, then curl the handles up towards the shoulders and squeeze for a beat at full flexion.

Lower over about three seconds until the elbows are straight again, keeping the upper arms pressed into the pad the whole way, and curl again without letting the stack rest.

The mistakes that cost you the most

Elbows out of line with the pivot is the fault that spoils everything downstream. When your joint and the machine's axis disagree, the arm slides on the pad through the rep, the resistance arrives at the wrong points and your shoulders start compensating. Check it before you load, not after.

A seat set too low produces a version of the same problem, lifting the shoulders towards the ears and letting the armpits leave the pad. If you are shrugging at the top of every rep, raise the seat.

Half reps at the bottom trim the longest position out of every repetition. Schoenfeld and Grgic's review of range of motion and muscle development found fuller ranges generally favour growth, and Pallares and colleagues reached the same conclusion in their meta-analysis, so straighten the elbows.

Letting the stack slam back discards the eccentric. Schoenfeld and colleagues found eccentric actions produce slightly greater hypertrophy than concentric ones, and controlling the return on a machine costs nothing.

And leaning back to finish a rep is simply the seated version of swinging a barbell curl.

Sets, reps and rest by goal

Moderate to high reps, short rest, and no need for heroics with the pin.

For muscle gain, three sets of ten to fifteen with a minute. For strength, three sets of eight to twelve with ninety seconds. In a fat loss phase, three sets of fifteen to twenty with forty five seconds.

Take the last set to genuine failure. This is one of the few exercises where the final rep carries no consequence beyond the handles stopping, and it is worth using that.

Drop sets are easy here for the same reason. Move the pin, keep going, and you have added meaningful volume in under a minute without another warm-up.

Progress by reps within your range, then move the pin one plate. Selectorised stacks often jump in increments that are large relative to what your biceps can curl, so expect to add reps for a few weeks between load increases.

Schoenfeld and colleagues found a dose response between weekly hard sets and hypertrophy, and machine curls are an efficient way to accumulate those sets.

Refalo and colleagues found stopping a rep or two short of failure produces comparable growth to going all the way, so the earlier sets do not need to be maximal even though they safely could be.

Where it fits in your split

After the pulling, or as the main biceps exercise on an arm day.

On push, pull and legs it goes at the end of pull day, once rows and chin-ups have already loaded the elbow flexors hard. On a bro split it can come first or second for biceps on arm day. On an upper and lower split it serves as the curl in either upper session. On a full body programme it is quick, since setup is a seat and a pin.

There is a reasonable case for making this your primary curl. It loads the biceps well, it removes the cheating and it is the easiest curl to take to failure, which is where a lot of arm training quietly falls short.

The case against is that it does not load the stretched position. If this is your only curl, add something that does, such as an incline dumbbell curl, and the pair covers the range properly.

Twice a week is sensible. The biceps are small, recover quickly and already get worked by everything you pull.

Variations worth knowing

The preacher curl is the free weight equivalent, with a barbell or dumbbells over an angled pad, and it trains almost exactly the same thing.

A single arm machine curl, on machines with independent handles, exposes side to side differences that a two arm version happily hides.

The cable curl offers a freer path with constant tension, which is useful when the machine's fixed spacing does not suit your wrists.

The incline dumbbell curl loads the stretched position and is the natural partner rather than a rival.

The hammer curl uses a neutral grip and shifts work towards brachialis and brachioradialis, which builds arm and forearm thickness.

And some machines offer neutral handles for a machine hammer curl, which gives you that grip with the same seated support.

What the evidence says

Marcolin and colleagues compared curl variants and found the balance of activity between biceps brachii and brachioradialis shifts with arm position and grip, which is the honest description of what separates one curl from another.

Vigotsky and colleagues cautioned that surface electromyography amplitude cannot be read directly as a measure of growth, which is worth holding onto whenever a machine is marketed as activating the biceps more than free weights.

Schoenfeld and Grgic reviewed range of motion and muscle development and concluded fuller ranges generally favour hypertrophy, supporting the full straightening of the elbow at the bottom of each rep.

Pallares and colleagues found full range training beat partial range training for strength and hypertrophy in their meta-analysis, which points the same way.

Schoenfeld and colleagues found eccentric muscle actions produced slightly greater hypertrophy than concentric ones, supporting a controlled three second return rather than a dropped stack.

Schoenfeld and colleagues also found a dose response between weekly hard sets and hypertrophy, and Refalo and colleagues found sets stopped short of failure grow muscle comparably to sets taken to it, which is how to decide when to use the machine's safety.

Common questions

Is a machine curl worse than free weights?

For growing the biceps, no. It loads the elbow flexors through a decent range with the cheating removed, and it lets you train to failure without any awkwardness. What you give up is the small amount of stabilising work a dumbbell or barbell demands, which is not why anyone does curls.

How do I set the seat?

So the pad meets the back of your upper arms and your elbows line up with the machine's pivot. If your shoulders shrug at the top or your arms slide on the pad during the rep, the height is wrong.

Is this the same as a preacher curl?

Close enough that doing both in one session is redundant. A preacher curl uses a free weight over an angled pad; the machine fixes the path and varies the resistance through the range. Use whichever is free and stop worrying about it.

Should I train to failure?

On the last set, yes. It is safe, it takes seconds and it guarantees the effort was real. Earlier sets can stay a rep or two in reserve, which produces comparable growth with less fatigue.

Do I need this if I already do chin-ups and rows?

Not strictly. Pulling loads the elbow flexors hard, and plenty of people build good arms without direct curls. If biceps size is a priority, though, a few dedicated sets a week are a cheap addition, and a machine is the least demanding way to get them.