The most effective biceps exercise- a biomechanical perspective

The biceps muscles

Which muscle do you most often imagine when strength or weight training comes up in conversation? It’s usually the biceps. Most people will raise their arm to the side and show their guns. They’ll flex their biceps, or at least mime it. But how do you grow your guns, what’s the most effective biceps exercise?

The biceps are showcase muscles, beach muscles. And they’re popular muscles to train for that reason. But a lot of gym-goers will toil away without really getting the guns they were hoping for. Why is that? In my view, it’s for two reasons

• A lot of trainers don’t do the big basics – deadlifts, squats, bench press, pull-ups, rows. Only some of these stimulate the biceps to any significant degree, but it’s the whole-body brute strength and hormonal cascade that will help you grow all over.
• Many people choose exercises that allow them to put the lifting force through lots of other muscles other than the biceps. So, the biceps don’t get the stimulation they need.

Biceps training isn’t complicated. Although there are lots of different exercises, they pretty much all boil down to one movement – biceps curls. Hold a weight, flex the elbow. Yes, you can rotate the wrist, but that’s not the main contributor to biceps muscle activation. Elbow flexion – that’s the action. So how can so many trainers get so little out of their biceps training?

In this post, I’ll answer that question. I take a look at the biceps curl from a biomechanical viewpoint and give you my recommendation on the most effective biceps exercise for really stimulating those muscle fibres.

The problem with standing barbell curls.

Subscribe to any training magazine and, pretty soon, you’ll find an article espousing the merits of the standing EZ bar curl. Often, it’ll be because ‘you can use the most weight’. It’s a good exercise, but is it as effective as it should be?

I don’t think so. And here’s why: there is too much opportunity to get the weight up using other muscles or for other muscles to fail before the biceps.



Here are the common issues:

• Arching the lower back to assist in getting the weight up.
• Allowing the elbows to fall behind the body as the weight is lowered, thereby taking the strain off the biceps at that crucial mid-rep peak contraction.
• Using the front delts to raise the angle of the upper arm. Again, that gets you past the crucial mid-rep sticking point with assistance from the delts.
• Using a little leg dip and ‘popping’ the weight up by initiating the movement with the legs.
• If you manage to control all these potential form issues, you’ll find that it’s a massive stimulator of the core, especially as you get to curl appreciable weight. I find the core activation is intense and distracting. I’m training my biceps, after all, not my core! I’m sure that I sometimes miss the last rep because I’m knackered and my core is shot.

There is one thing about this exercise I quite like, and that’s the ability to go to absolute failure. Once you fail on the positive part of your reps, you can do cheat curls – start throwing the weight up and fighting the negative down, eventually failing on the negative to achieve absolute failure. It’s brutal and effective.

So, there is a place for standing curls. But, if we assume you’re unconsciously making one or more of the above execution mistakes, and you’re definitely not doing the cheat reps, then, in general, they’re a poor choice for most recreational lifters. I’d extend that statement to most biceps exercises. Any exercise that requires you to stabilise your body, recruit your core or give you scope to take the strain off the biceps is probably going to lead to sub-optimal development of the muscle. Dumbbell curls, even seated, allow for various compromises. Cable curls, single-arm curls, hammer curls, even concentration curls – they’re all cheatable because there is instability.

A better focus on the biceps

So, what’s the answer? You need to take away instability and the opportunity for other muscles to take over. Lock the body in position and lock the upper arm in place. You know where this is going, right? Preacher curls.

Preacher curls lock you in position, and they lock your upper arm. Assuming you keep your wrists locked, the only joint you can move is the elbow joint. And there’s very little core engagement, so there’s no distraction. It’s pure biceps with 100% focus on the target muscle.

But…

Yes, there’s a but. Preacher curls have their flaws too. To understand why, let’s take an excursion and look more closely at the biomechanics of a biceps curl.

Biomechanics of a standard biceps curl

For this analysis, let’s assume we have a simple biomechanical system, as shown. The biceps muscle originates at the top of the upper arm at an acute angle and inserts a short distance from the elbow joint. We can draw a ‘force vector’ to represent the direction of the force required of the biceps to counteract the weight. We can further break that force vector down into two forces acting at right angles: one that rotates the arm, acting at right angles to the forearm, and another that stabilises, acting along the forearm. It’s the rotary force we’re interested in – that’s the one that requires the muscle fibres to shorten when you flex the elbow.

As the angle of the forearm varies, the force required to counteract the weight varies. Although the combined force vector changes very little in its direction, the rotary and stabilising components vary in both magnitude and direction as the angle varies.

When you fully extend the arm, the weight is acting straight down the forearm and is not creating a rotational force. So, at full extension, the rotary component of muscle force is zero. All that is left is the stabilising component which, at full extension, is almost entirely provided by connective tissue – ligaments, tendons, fascia and so on.

When the arm is fully flexed – let’s call that 80° – again there is very little rotational force acting on the arm and so the rotary muscle force is still small.

When the arm is horizontal, the torque produced by the weight is at its maximum, and it exerts a strong rotational force on the arm. At this point the required rotary muscle force is at its peak.

Force angle relationships

You can see this in the chart of the rotary force component. Notice how the force drops to zero at a forearm angle of 90° to the horizontal, i.e., hanging straight down. Notice also that the rotary force peaks at 0°, i.e., horizontal forearm. You’ll spot that the force produced by the biceps is large, at nearly twice bodyweight for a 20kg weight and a person weighing 87kg. For the SI purists, I have the numbers in Newtons, but felt that was a little abstract for this article.

Finally, see how the stabilising force increases as the arm extends. You’d expect this, as the fibres and connective tissues lengthen, they will come under increasing tension.

The muscle length-force relationship

Ok, so the force imposed on the biceps changes as you curl the weight and the angle changes. So what? Well, the rotary force curve maps quite well onto the length-force relationship of muscle fibres. Huh? Say that again. Well, as a muscle is lengthened and shortened, its strength changes. The strength change with length change (length-force relationship) is similar to the strength requirement with angle change (the rotary force curve). A muscle generates the most force when it is at ‘resting length’, approximately the middle of the range. As the muscle lengthens, its ability to generate force decreases and, as it shortens, it also decreases. If you look at the shape of this length-force curve below, you’ll see it’s similar to the rotary force curve above.

But not only that, the peaks in the two curves align. In the biceps curl, the middle of the range, where  the muscle is able to generate the most force, is around the point where the forearm is horizontal. That’s great, because in the biomechanical model just presented, that’s also the point where the muscle is required to generate the most force. So, to restate, the force-angle relationship maps well to the force-length relationship.

Why is the muscle stronger at the middle of the range? Because that’s where, at the microscopic level, the arrangement of the protein filaments in a muscle fibre is most optimal. At the midpoint, you get the greatest crossover between the actin and myosin filaments, so the binding is strongest. When you lengthen the muscle, there is less overlap, and the binding is incomplete. And when you shorten it, the actin filaments overlap, and this ‘interferes’ with the effectiveness of the actin-myosin binding.

Standard curl biomechanics wrap-up

So, summarising the discussion on forces: any curl where the biceps is in the middle of its range when the weight is creating the most force, is going to allow you to use the most weight. It’s going to require the most force, use the most energy, generate the strongest interaction between protein filaments and produce more metabolic by-products. The result will be a stronger stimulus for adaptation.

Those statements are only valid, of course, if you don’t cheat the weight up. But, as we already identified, the average lifter is going to find it hard not to! It’s the body’s instinct to recruit whatever muscles it needs to get the weight up. It requires a lot of focus to prevent other muscles getting involved.

The preacher curl

As we already established, the preacher curl really isolates the biceps, but it has some flaws. Now that we have covered the biomechanics, we can look at why the standard EZ bar preacher curl is sub-optimal.

It has a sub-optimal force-length mapping

Almost all preacher curl benches have an angled pad where you drape your arms over the top. That pad is typically at 60° to the horizontal and locks the upper arm at that angle. That changes the biomechanics. When the forearm is horizontal, and the weight is producing the most rotational force, the elbow is no longer at 90° and the biceps is no longer at its midpoint of its length. Instead, the elbow is at 120° and the biceps is approximately 135% of its resting length.

Although the peak force requirement is the same as a standard curl, you’re putting the most force through the biceps when it is capable of generating only about 80% of its peak force. There is less overlap of the actin and myosin filaments, the binding is less strong, and the metabolic cost is less. There is less scope for stimulating adaptations.

I should just point out that these graphs are only a model. The model shows the same peak force of around 1.8 bodyweight and assumes the same weight is lifted. In reality, because you’re effectively weaker at 135% of resting length, you won’t be able to lift the same weight. That’s why you’ll find the amount of weight you can lift with the preacher curl is less than with a standard curl.

There is a reduced range of motion and less work done

That’s not the only issue with the standard preacher curl. If you look at the force graphs, you’ll see the rotational force has an endpoint where you physically can’t lower your arm any more. You’ll also see that the rotational force required of the biceps drops to zero at the top of the movement. In fact, if you go further than 90°, which is entirely possible with the preacher curl, you’ll get some assistance to curl the weight! So, the useful range is a lot shorter on the preacher curl and the area under the curve, which is a proxy for ‘work done’, is less.

It has a risky stretch

And there’s more! We are told that the preacher curl is ‘all about the stretch’. Get the full stretch at the bottom and stop short of vertical to keep the tension on the muscle – that’s the ‘correct’ way to do preacher curls. You’ll be sore the next day if you do it the ‘correct’ way (sore is a good thing if you’re a bodybuilder!). But is that sensible?

Take a look at the stabilisation force curve. The force becomes very high as you approach full extension. There’s still a significant amount of downward rotational force being generated by the weight as you approach the fully extended position, and this gives rise to an intense ‘stretch’ sensation. A lot of trainers stop short of this position because it feels unpleasant and risky. It feels like you’re going to rip something. And, looking at the stabilising force chart, so you might! Most of the tension generated by this force is taken up by connective tissue. No wonder the preacher curl can make you sore. Should you really be subjecting your tendons to this kind of tension? Perhaps not.

So, although you can put all the focus into your biceps with a standard preacher curl, it has some limitations that might make you choose to avoid it.

The most effective biceps exercise – the best of both worlds

Can you get the best of both worlds? A curl that maximises the load at the midpoint and that also anchors the body and upper arm for maximum biceps focus?

Yes, you can! There are two possibilities.

Use the other side

Some preacher curl benches have two sides, one sloped and one vertical. Just use the vertical side. That way you achieve the biomechanics of a standard curl, but with the stability and focus of a standard preacher curl. However, most gyms have a built-in seat that means you have to use the sloped side. And our studio has a bench ‘attachment’ with only one side. But don’t worry, there’s another option.

Use a cable

If you are able to, move the preacher bench in front of a cable stack and position it at a distance that brings the cable in at the same angle as the preacher bench. Effectively, you’ve moved gravity to act at 30° to the usual vertical. So gravity is once again parallel to the upper arm, and we restore the biomechanics of the standard curl we saw earlier.

I prefer this version to using the vertical side of a preacher bench. With the cable version, you can sit in the seat and use the bench in the way it was intended. When you use the vertical side of a bench with a barbell, you have to find a way to anchor yourself because there’s usually no seat.

Another feature of this version is that you still get a lot of tension at the top of the movement. So, when your forearm is vertical, you’re still working hard to counteract the weight. This is great for squeezing the biceps. If you’re a physique competitor and you have to squeeze your biceps, then this will help you get used to flexing hard in the fully contracted position and accustom you to the discomfort.

Summary

The eagle-eyed among you may have noticed that in our previous blog on the top 5 biceps exercises, we didn’t mention the cable preacher curl. That’s because the ‘top 5’ series also tried to choose accessible exercises. Almost all gyms will have a preacher bench but in very few will you be able to move that in front of the cable stack. This article ignores accessibility and looks purely at effectiveness.

So, my recommendation for the most effective biceps exercise is the cable preacher curl. It’s a no-cheat exercise, enables 100% focus on the target muscle and is biomechanically optimal for the most effective muscle adaptations. That means growth – if you want big guns, do cable preacher curls.