Do Dumbbells or Barbells Produce Superior Results?

Dec 27

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Takeaway Points:

Most lifters train primarily with bilateral exercises, in which both arms or legs are working simultaneously.
However, unilateral exercises, in which individual limbs act with independent loading, have their own strengths and weaknesses - and they may be superior depending on your training needs.
Here I analyze some of the strengths and weaknesses of each.

Many exercises can be classified as either bilateral (using two arms/legs simultaneously) or as unilateral (using arms/legs individually).

For example, a squat is bilateral because it uses both legs at once, while a lunge is unilateral because you primarily stress each leg individually. There are also examples of exercises where it is possible to train the limbs unilaterally, but while moving both at the same time. A good example is the comparison between the barbell bench press (bilateral) and the dumbbell bench press - the dumbbell bench press, despite involving both arms moving at the same time, is unilateral because each arm has its own weight and is thus being individually worked. The same applies to many other dumbbell exercises, which are often unilateral even when using both arms at the same time (overhead presses, lateral raises, upright rows, dumbbell rows, and so on).

What is the benefit of using one approach or the other, especially when both kinds are available?

Correcting Strength Imbalances

Many individuals will start off as beginners with some kind of strength imbalance. The reality is that in the real world, loading is not as precise and carefully measured as what we can apply in the gym - so very often, one side of our body tends to get a bit stronger than the other. This is partly due to things like hand dominance - if you’re right hand dominant, you tend to use that hand to pick up loads and carry them around a lot more frequently than your left hand. It may not seem like much, but over time these little exertions will add up to your right arm tending to be stronger than your left, even if you don’t build any muscle out of the process.

Likewise, we all tend to carry things in certain habitual ways, and we don’t tend to carefully even out the load. Women tend to carry bags which load one side of the body and not the other, everyone tends to carry briefcases and bags and other types of loads which are not evenly distributed. These add up, such that most people who go into the gym are coming in with some kind of strength imbalance.

Luckily, as mentioned above, we can apply a lot more precise (and heavier) loading when going to the gym. If you have a slight imbalance from carrying around a 10lb bag in one hand, for example, this is quickly going to get overpowered by the strength and muscle building stimulus you get when you start exercising with a 20lb or 30lb weight in both hands. So, very often, these imbalances quickly go away once you get exposed to heavier, more consistent training, and it’s not something that has to be worried about.

However, it’s not always immediately fixed. If you have a severe imbalance, and you train primarily using bilateral movements in the gym, your stronger side can get used to habitually making up for your weaker side - and so your stronger side keeps getting stronger while your weaker side doesn’t, and this can even increase the imbalance. This can be seen when someone is squatting or bench pressing with a barbell, for example, and they struggle to keep both sides of the barbell moving evenly. One arm or leg may noticeably lock out before the other.

In such a case, training should shift to primarily using unilateral movements until this issue is fixed. Dumbbell bench presses, lunges, alternating split stance deadlifts, dumbbell overhead presses, and dumbbell rows should make up the staples of your training, and barbell versions should be avoided where possible. Some machines make it easy to train unilaterally, while in other cases you may have to get creative in order to use machines which are normally designed for bilateral exercises.

Core Work

Another benefit of unilateral work is that it tends to place a greater emphasis on the core. As your arms and legs are located on the outside of your torso, and as one of the jobs of your core is to keep your torso from excessively rotating, this means that using only one arm or leg at a time is naturally going to load up one side of your torso more heavily than the other, thus engaging the core to help prevent rotation.

As a result, some unilateral exercises can be a very effective way to also train your core at the same time. Alternating one arm rows, single arm bench presses, single arm overhead presses, lunges weighted on one side, and alternating stance deadlifts - all of these can be used to train the core at the same time as working on the primary movement. This can be especially useful if you are someone who needs a lot of core training, as it will save you a bit of time. Many beginners also tend to have a weak core, and so training the core in this rotational aspect can be very helpful in terms of getting them ready for training safely with heavier barbell movements.

For field athletes, the demands of forces on the body are often unpredictable. Rotational training for the core is thus important, as it will help the core to better protect the torso, as well as aiding in the transmission of force from the lower to upper body and vice versa.

Field Athletes and the Bilateral Deficit

Another common recommendation is that unilateral exercises are superior to bilateral exercises when it comes to field athletes. This one will take a bit longer to unpack.

A well known phenomenon is called the “bilateral deficit”. Studies performed on the strength in individual limbs found a curious effect - that when you take the strength of an individual limb and multiply it by 2, the strength of both limbs working together is actually slightly less than what we would expect from that predicted number. This is referred to as the bilateral deficit - the implication that bilateral exercises are somehow “missing” or “lacking” some amount of strength that should exist due to the strength of the individual limbs.

Proposed reasons for this deficit are wide ranging. Maybe the body is just better at doing single limb exercises, and these are more natural for it. Maybe you didn’t train in a way that properly maximizes your strength adaptations.

Based on the existence of the bilateral deficit, and the fact of the added rotational core effect mentioned above, some coaches have hypothesized that unilateral exercises would be a superior method of training. After all, if you are slightly stronger with each arm individually, why not train the arms bilaterally, take advantage of this effect, get even stronger, and thus have a slight edge over those who primarily train bilaterally. Mike Boyle, for example, is a huge proponent of training unilaterally, and uses it as a main training method for athletes.

I do think it’s likely that there is some slight edge, especially for young athletes at the very beginning of their career, primarily for the core benefits already explored above.

However, it is important to know that research since seems to have turned against the concept of the bilateral deficit slightly - as far as I’m aware, the current consensus is that it is likely an artifact of the way that the previous research was constructed, and that the deficit is likely to be small or nonexistent. Further, it seems that the deficit can be trained away rather quickly, so it seems unlikely to be worth basing an entire training system on. In short, there may certainly be benefits to unilateral training, but it seems unlikely that the bilateral deficit should be the primary reason to choose this method of training.

Greater Range of Motion

Another benefit of the unilateral exercise is that sometimes, they may have greater range of motion than their corresponding barbell variation.

A barbell bench press, for example, is slightly limited in its range of motion due to the bar being stopped by the torso. In contrast, a dumbbell bench press does not have the bar connecting the two weights, so you can likely get a bit deeper.

Since range of motion is a huge factor in terms of how much muscle you build, and since more range of motion is generally better, this can be a meaningful difference over a long period of time.

However, since dumbbell bench presses would also be less specific than barbell bench presses in terms of building strength in the barbell bench press, this also means that this method would be less likely to be useful for powerlifters, who need to maximize their strength in the barbell bench press. Thus, such a method is more likely to benefit bodybuilders, general fitness, and field athlete exercisers, especially when the reps are done with a full, controlled, deep range of motion.

Training With Minimal Equipment

Since training a bilateral exercise means working out both limbs at once, a comparatively larger amount of weight is needed in order to provide a challenge.

A bodyweight squat for a 200lb exerciser, for example, applies about 100lbs per leg. A bodyweight lunge does not put all 200lbs individually on each leg (some weight goes into the back leg in the process of using it to stabilize), but it is closer to 200lbs than to 100lbs - so, this is a naturally more difficult exercise, in that it starts out with more weight on a single limb.

Likewise, when adding weight, one must be more careful to add weight when training unilaterally when compared to training bilaterally. Adding 5lbs to a barbell bench press means that each arm will only feel 2.5lbs extra, while adding 5lbs to a dumbbell bench press means that each arm feels that full 5lbs extra.

As a result, unilateral exercises don’t require the same amount of weight to be challenging. This can be useful when you don’t have much to work with - for example, home or travel workouts. By relying on unilateral exercises, you can keep workouts challenging with less added weight or equipment involved. Lunges, single arm pushups, and single arm pullups are always more challenging than their corresponding double-limb counterparts, and variations on these exercises (archer pushups, archer pullups) can be a good way to maximize the challenge while minimizing the necessary additional equipment.

Negatives To Unilateral Training

Above positive effects noted, there are certainly some drawbacks to unilateral training.

One major drawback is that it takes longer to train when training limbs individually. A single arm dumbbell row, for example takes twice as long to get in the same stimulus evenly across both limbs as it would take to do with a barbell row instead. The additional time spent moving also means that there will be greater exhaustion placed on the central metabolic system in the process.

As a result, training with unilateral exercises can sometimes be a bit more exhausting and boring compared to bilateral exercises. However, this can often be avoided with careful exercise selection. A single arm dumbbell row may take twice as long, for example, but a batwing row enables you to train both arms simultaneously, while also still enabling them to work unilaterally. Some leg machines enable you to do leg presses, leg extensions, or leg curls with individual weights on each leg as well - so it is possible to speed up the process a bit if you know what to look for and how to manage it.

Another problem is simply that unilateral exercises often do not “scale” as easily and cleanly as barbell exercises. That is to say that unilateral exercises may not be able to add weight as easily and consistently when compared to bilateral, barbell-loaded exercises.

Dumbbells, for example, often jump up in increments of 5lbs - and since that’s for each dumbbell, that means that a jump from 45lbs per hand to 50lbs per hand is equivalent to 5lbsx2 = a 10lb jump, moving from 90lbs to 100lbs - about an 11% increase in weight, which may be difficult to manage. In contrast, a barbell can be loaded up with smaller 2.5lb plates, enabling you to jump from 90lbs to 95lbs to 100lbs - with fractional plates, the jumps can be even smaller.

Dumbbell loading is also sometimes difficult. A squat loaded with 100lbs on a barbell, for example, can be very easily done, and the weight can be placed on the back where it is stable and easy to control - by contrast, there is no easy way to do the same with dumbbells - you could hold them hanging from the hands, but then it is hard to hold onto them for the duration of the lift if they are heavy enough - you could try to hold them at the shoulders but this is awkward and unstable if they are heavy enough. When it comes to dumbbell loaded bench presses and overhead presses, it can get harder and harder to get the dumbbells into a pressing position without assistance from a friend, or risking injury.

In short, when exercises get heavier, dumbbells get more and more awkward as a loading method.

Many gyms also do not have sufficiently heavy dumbbells to challenge very strong individuals. Most gyms only have dumbbells that go up to 100lbs or 125lbs per hand - this is more than enough for most beginners, but heavy, well-trained lifters can often easily handle much more than this when bench pressing, deadifting, squatting, etc. As a result, these lifters would basically be forced to switch over to barbells at this point in order to be able to continue training and getting stronger.

I’ve seen many videos of what can happen when this is taken to its extreme - individuals training split squats while wearing a weight vest, weights hanging from the vest, additional weight held in the hands, so heavy that they can barely knock out a few unsteady reps before dropping it - it looks rather silly, and is evidently impractical. It would be way easier to simply load up a barbell and go at it.

So, it is evident that at higher training levels, many unilateral exercises simply don’t scale well. You can’t add weight forever and have these exercises remain just as doable. In contrast, the barbell scales very well - with the use of a rack, you can carefully control the starting position for each lift, you can add weight steadily and consistently in small amounts, and you have spotter guards which make it easy to bail in the case of failure - in short, everything is much better controlled.

There are some exercises where unilateral work can be made to scale really well. Farmer’s handles, for example, enable you to perform farmer’s carries at virtually any weight. However, equipment like this is generally specialized in nature, meaning that it’s more expensive and less likely to be found at your local gym. As a result, for many it simply naturally makes more sense to start focusing more and more on bilateral exercises as you get stronger.

Still, some sports may still get great use out of unilateral exercises. Field athletes will still get benefit of the core effects, and sports like strongman sometimes make use of unilateral exercises like the circus dumbbell, so it still makes sense to train for these events.

Wrapping It Up

Unilateral work will most often be useful for beginners, who are likely to have issues with core stability or with strength imbalances from one side to the other.

Strongmen may benefit from unilateral work, especially to prepare for specific strength events.

Bodybuilders may prefer dumbbell work (if they have sufficiently heavy dumbbells) if it enables them to get a greater range of motion on certain exercises and thus build more muscle.

Calisthenics/gymnastics athletes may benefit from single arm work when it comes to building exercises like the single arm pushup or single arm pullup.

Powerlifters are not likely to benefit, due to the decreased specificity of the unilateral versions of exercises, compared to the bilateral versions in which powerlifters compete. However, they may still benefit if they need to iron out imbalances, or if in a size-focused phase where specificity is less important.

Sport and field athletes will likely benefit from training limbs individually, simply because their bodies are likely to deal with unexpected forces and positions, and they likely need limbs to be trained to function individually. These types of exercisers also benefit from the added core strength that can be trained with unilateral exercises.

Runners and other endurance athletes will benefit from various general benefits mentioned above, but are not likely to get much in the way of “unique” benefits compared to the general benefits seem from bilateral weight training.

Unilateral exercises can be of unique benefit when training with little to no available equipment.

About Adam Fisher

Adam is an experienced fitness coach and blogger who's been blogging and coaching since 2012, and lifting since 2006. He's written for numerous major health publications, including Personal Trainer Development Center, T-Nation, Bodybuilding.com, Fitocracy, and Juggernaut Training Systems.

During that time he has coached hundreds of individuals of all levels of fitness, including competitive powerlifters and older exercisers regaining the strength to walk up a flight of stairs. His own training revolves around bodybuilding and powerlifting, in which he’s competed.

Adam writes about fitness, health, science, philosophy, personal finance, self-improvement, productivity, the good life, and everything else that interests him. When he's not writing or lifting, he's usually hanging out with his cats or feeding his video game addiction.

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