Ask A Personal Trainer: Dumbbells vs. Barbells

  • Brace yourself as this blog post contains a little maths. Understanding the different result and effect you can expect when using dumbbells vs. barbells is useful. It can help you make better choices when deciding which workout programme may best suit your goals.
  • Most of us are capable of producing a little less than twice the force when working two limbs together (as with a barbell bench press) than we can by adding together the combined weight lifted by each limb independently (as with a dumbbell bench press).

To use another example: if you can perform a set of leg extensions with 25kgs when using one-leg at a time, you would be able to lift approximately 45kgs when using both legs together i.e. “not quite as much”.

  • The difference in strength described above, is known as the bilateral deficit and this deficit is typically around 10% in new exercisers. Deciding
  • The bilateral deficit is made larger by frequently training with dumbbells instead of barbells or, working one-limb at a time.

Dumbbells vs. Barbells; which is best?

When working with personal training clients, or those using our Online Program, correcting discrepancy in strength between right and left side is a priority. Why? Because you’re less likely to sustain injury if you’re balanced. In fact, I would rather you were equally weak than be very strong with your right arm and less so with your left arm. However, there is not much hard research on the subject of strength discrepancy, as it relates to injury. This theory is based on our experience and various professionals we respect currently working in strength and conditioning.


Research-based evidence does exist that being balanced leads to improved sports performance. To you and I, this may mean that there is hard evidence in the dumbbells vs. barbells debate… Researchers in strength and conditioning have been studying the bilateral deficit, and how to augment it, since the term was first coined in 1961 (Henry & Smith). Let’s skim the surface!


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Why do we have a strength deficit?

There are a small number of reasons why we have a bilateral deficit and the primary is; task familiarity.


Most of our day-to-day movements are reciprocal. One limb will move independently of the other when walking, running, climbing etc. It makes sense then that we learn new movements more efficiently when exposed to them (or practicing them) one limb at a time. It’s not that we are designed to workout with only one limb at a time, as studies have shown consistently that this bilateral strength deficit decreases over time.


Only one study to date has examined the effect of the bilateral deficit on sports performance, finding that sprinters with a smaller bilateral deficit are able to produce more force ‘off the blocks’ than those with a larger deficit. The more balanced we are (in theory) the more explosive/stronger we are.



Our strength discrepancy between limbs is normal and unavoidable as we develop as humans with a dominant side (for whatever reason). The bilateral strength deficit is always present but can be reduced/improved over time with effective exercise programming. However, one of the goals of your training program should be to reduce discrepancy between right and left side, and reduce your bilateral deficit.


Hard science on this subject is lacking and far from conclusive. However, a number of things are likely and important to consider if training for longevity:

1.     Beginners to strength training will likely demonstrate a large strength deficit.

2.     Learning new movements might best be done one limb at a time.

3.     Balance is never a bad thing. Whilst we do not yet have proof, it’s likely that bringing strength in to balance reduces injury and improves general physical performance.


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Thank you for reading.

If you have questions, I’d be happy to answer them in the comment section below.





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