What EMG actually tells us about muscle growth

written by Philip Stefanov  |  SEPTEMBER 5, 2023

Electromyography (EMG) has been a hot topic in the fitness world for quite a while. On the one hand, some people live by it, often citing scientific findings and claiming certain exercises and variations to be superior for growth because of EMG data.

But, on the other hand, we have those who aren’t impressed with EMG and go as far as to label it as useless when it comes to getting valuable insight for practical training purposes.

So, who is right? Let’s talk about it.

What is EMG, Exactly?

EMG, which stands for electromyography, measures the electrical activity in muscles during physical activity. It measures the strength and intensity of the nervous system signals to our muscles and picks up on some electrical activity from peripheral factors in our muscles.

In other words, EMG doesn’t directly measure muscle contractions but the electrical signals that precede them. It also isn’t 100 percent accurate, especially because the most popular and non-intrusive way of tracking EMG is to place electrodes on our skin and make them stick with a gel or tape.

That said, when measured by experienced people, EMG can be relatively accurate and serve as a proxy for measuring muscle activation. Because of that, EMG is often used to determine what training variables might be more advantageous for growth. EMG is often measured in studies comparing:

  • Exercise variations (e.g., high vs. low-bar squat)
  • Different exercises (e.g., back squat vs. hip thrust)
  • Load variations (e.g., 50% of 1RM vs. 80% of 1RM)
  • Training technique
  • Ranges of motion (e.g., full squat vs. half squat)

The idea is that if a specific variable yields stronger EMG activity, it likely means stronger contractions, which probably predicts better results. But is that the case?

Does EMG Predict Hypertrophy?

This is where things get fuzzy because the actual answer is “Not necessarily.” While a helpful data point, EMG is imperfect and has some limitations. Let’s look at 7 of them:

1. Heavy Load Bias

EMG readings heavily favor heavier loads over lighter ones. When compared, heavy sets elicit much higher EMG readings than lighter ones, but does that mean high-intensity training is more valuable for growth?

No, because research shows that growth can occur at various intensities (at least from 5 to 30+ reps), given enough effort.

2. Short Muscle Length Bias

EMG readings tend to peak when muscles shorten (say, the top half of a bicep curl) and decrease as the muscle lengthens. However, all portions of the range of motion are beneficial for actual growth.

If anything, growth might appear more effectively when muscles are lengthened (stretched) under load, which is when EMG readings are lower on average.

3. Isometric Contraction Bias

Isometric contractions (where the muscle doesn’t lengthen or shorten) show some of the highest EMG readings. Concentrics (the shortening phase) are typically the second highest, and eccentrics (the lengthening; negative) show the lowest EMG readings.

While each type of contraction is valuable, and the difference between their overall impact is likely small, we could argue that growth occurs in the opposite order:

  • Eccentrics - the most beneficial
  • Concentrics - the second best
  • Concentrics - the third best

4. It Looks At Superficial Electrical Activity

Electrodes only detect superficial muscle activity because there is no skin penetration in typical EMG tests.

This could be particularly troublesome for folks with a higher body fat percentage and a thicker layer of adipose tissue covering their muscles.

5. It Only Measures Nervous System Activity

EMG measures nervous system activity but not other things affecting muscle growth, such as metabolic fatigue. For example, as you accumulate metabolites in your muscles, nerve signaling could become impaired, leading to lower EMG readings.

This could lead people to believe that less growth would occur from ‘pump’ training where, in reality, this isn’t true. We know how valuable metabolic stress is for hypertrophy.

6. Proper Electrode Position is Crucial

How experienced someone is with EMG readings can significantly impact their findings. Placing the electrodes in the correct places and far enough from one another is necessary for getting more accurate readings.

For example, let’s say that you place two electrodes too close. They could pick up some activity from each other, leading to higher (but inaccurate) readings.

Similarly, if the electrode is not in the correct position, it could struggle to pick up electrical activity even if the muscle works hard and gets a fantastic stimulus.

7. The Tech Used Can Go Bad

While most people don’t think about the technical minutia when reading studies, it’s important to remember that data is typically gathered with tech devices.

EMG is straightforward and intuitive, but it can also encounter issues. Electrodes and wires can go bad, and the unit itself can malfunction. Each of these things can impact readings and EMG data.

So, How Valuable is EMG Data?

The above limitations might make it seem like EMG is useless, which is not the case. EMG data is a great start and could give trainees new ideas on how to train their muscles.

That said, always consider things like the pump, actual muscle fatigue, soreness, and the gradual decrease in performance as your workout progresses to gauge the effectiveness of your training.

Do your joints feel okay, and does the movement feel effective? While subjective, these things could tell you a lot about an exercise and if it works for you. If EMG data suggests an exercise is great and it works for you, keep going. However, if the activity or variation is supposedly good but doesn’t feel right, move on because EMG is just one thing, and it can be wrong.

Like any tool, EMG has limitations, which doesn’t mean its data is useless. Instead, we must learn to interpret results more carefully, consider the implications, and keep the potential limitations in mind.

Thanks for sticking around. I'll catch you next week!


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