If you have ever researched which exercise is best for a certain muscle, which variant is most effective or which muscle is the main one involved in a trick or movement, it is likely that you have come across people who answer this question based on readings of electromyography, devices with electrodes that measure the electrical impulse received by a certain muscle.

At first it may seem like a fairly accurate and logical method to resolve this type of issue and, many times, it is presented as the definitive test to know muscle activation but… is it really such a reliable method?

After seeing some quite dubious or controversial statements about some exercises using this method I decided to investigate the subject in depth and today I am going to show you what weak points electromyography has, what it can really be used for, what other methods we can use to know the muscles involved in an exercise and much more.

What is an electromyography and what does it specifically measure?

Electromyography (EMG) is a process that measures, usually superficially, the electrical signal that the brain sends to a muscle.

A common misconception is that electromyography measures muscle contraction, the strength of muscle fiber contraction, or muscle activation directly. This is not really the case, as we just said, what the EMG really measures is the electrical impulse that the brain sends to the muscle, which is known as neuromuscular excitation. This is very important because neuromuscular excitation is obviously a factor in the activation of a muscle and its contraction, but it does not have to be necessarily a directly proportional relationship.

Weak points of electromyography as a reference for muscle activation

In other words, the fact that the EMG records greater neuromuscular excitation in a muscle during a movement does not have to unequivocally mean that that muscle is becoming more activated or experiencing a stronger contraction. There are some intermediate steps between neuromuscular excitation and contraction that can affect the process.

In addition, we mentioned that electromyography is generally performed superficially, with electrode patches, since to make a deep measurement it would require inserting needles and this is not usually feasible or ethical in many cases.

The problem with this superficiality is that muscles do not have all their fibers close to the surface of our skin, but they also have a deep part that is not registered. If the muscle we want to measure has greater activation in the deep fibers, the EMG reading will be misleading.

Another weakness of electromyography appears to come from the angles at which the muscle is positioned when it is measured.

In a very curious study, researchers sent the same amount of electricity to the tibialis muscle and measured the EMG readings by placing it at different angles. The result should have been the same but different “muscle activations” were obtained at the different angles. Therefore, electromyography seems to have its results affected simply because the person is in one position or another.

In this other study, the recording of traditional superficial EMG and the recording of EMG with intramuscular electrodes, with inserted needles, were compared for the activity of the serratus anterior during different exercises and it was seen that in several shoulder movements the superficial electromyography significantly underestimated the activation of this muscle. So, depending on the angle or type of exercise, the superficial EMG could give an erroneous reading compared to the intramuscular EMG.

You must also take into account the passive tension that a muscle can experience. In certain exercises, a muscle can receive a greater stimulus without greater activation, just due to the position or the characteristics of the exercise.

To understand this, we see below an example where the EMG does not show a great activation of the long head of the biceps, however, it is working in an extended position, receiving more mechanical tension and, therefore, obtaining a stimulation of very effective growth. If you want to know more about the topic of extension work, I recently uploaded an article talking about the topic.

In short, there are many factors that can make the reading that electromyography gives not help us to know with certainty if that muscle is receiving a better stimulus or if it is the one that is being activated the most, or even it does not help us to know which muscle exerts the most force in a given movement.

Let's look at another example, in this study the EMG activation of the gluteus in its different parts was measured in two exercises: squat and hip thrust. The readings for the muscles in the gluteal area was always greater in the hip thrust compared to the squat.

However, after 9 weeks of training, glute growth was the same in those who did the squat and those who did the hip thrust, therefore, the EMG recording was not a good predictor to know if an exercise was more effective than the other for that set of muscles.

I have recently seen statements about which muscle is activated more in calisthenics exercises such as planche or front lever based on electromyography which, as we have just seen, is not the most reliable method, so I would not recommend using this technique as if it were an irrefutable method that shines the absolute truth. I think that, at most, it should be a support that provides clues for a more complete analysis in which other sources of information are used, such as knowledge on biomechanics applied to movement analysis.

Alternative methods to electromyography

I believe that currently there is no specific method that is 100% conclusive to determine if an exercise is more effective for a certain muscle, or which muscle is worked the most in each movement. Even worse when we talk about variants of the same exercise, different angles, or when we work with complex or compound exercises that do not isolate a specific muscle. For these cases, not even deep needle electromyography would give us a definitive reference.

Right now I think the best thing we can do is use the combination of different methods; such as knowledge about biomechanics, analyzing the internal moment of a muscle or the mechanical advantage to know what action each one performs, but also to know which muscle is in a more extended position, receives greater mechanical tension or passive tension, and to this we can complement it with techniques such as EMG or, if we do not have this possibility, the classic test of touching a muscle to see if it contracts or not.

Conclusion

In conclusion, electromyography can guide us and give us clues about the neuromuscular excitation of a specific muscle in a specific exercise, but it should not be considered a definitive test to affirm anything, since it has many blind spots and design flaws that can give misleading results. You must always rely on knowledge about biomechanics and take into account other factors that may be important and that the EMG does not indicate.

I hope it will help you,

Yerai Alonso

References:

https://jneuroengrehab.biomedcentral.com/articles/10.1186/s12984-017-0291-5

https://www.sciencedirect.com/science/article/abs/pii/S1050641114000285

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10349977/

https://www.researchgate.net/publication/371846115_Hip_thrust_and_back_squat_training_elicit_similar_gluteus_muscle_hypertrophy_and_transfer_similarly_to_the_deadlift