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Electromyography (EMG) Explained For Coaches

What is Electromyography?

Electromyography (EMG) measures the electrical activity within muscles during physical activity, such as performing a barbell squat. It doesn’t measure muscle contractions or their strength, only the nervous system signals that precede them. A common non-intrusive way to measure EMG is to attach electrodes to the skin at various parts of different muscles.

What is the Purpose of Electromyography?

One purpose of electromyography is to detect neuromuscular issues, such as muscular dystrophy, and nerve conditions, like peripheral neuropathies. 

Given EMG’s application in diagnostics, it can also be used as part of a treatment plan for various disorders to determine the extent of muscle and nerve damage and measure patients’ progress. 

As with strength and conditioning coaching, finding ways to monitor progress can help professionals make the necessary adjustments to treatment plans.

EMG is also a valuable research tool in the fitness field. It allows researchers to measure muscle activity on various exercises to determine which might be more effective under specific circumstances. 

Electromyography is often used to compare:

  • Variations of the same exercise (e.g., low-bar vs. high-bar back squat)
  • Different exercises (e.g., squat vs. hip thrust)
  • Load variations (e.g., 50% vs. 80% of 1RM)
  • Subtle shifts in technique (e.g., toes pointing slightly out vs. straight forward)
  • Range of motion (e.g., deep squats vs. half squats).

The data from such experiments is often valuable and provides coaches with in-depth insight into biomechanics that can help them build better workout plans. However, like any tool, EMG has limitations, so let’s discuss them next.

Some Limitations of Electromyography

Prevailing wisdom suggests that EMG readings predict muscle growth, with coaches often leaning on data when arguing about the effectiveness of different movements. But here are some limitations to keep in mind when interpreting the research:

1. There’s Bias For Heavy Loading

EMG readings tend to be much higher when participants use weights closer to their 1RM, which makes sense. Heavy loads take more effort to lift and force a higher recruitment of motor units.

Although heavier weights are more beneficial for strength development, research finds them equally effective as light and moderate loads for muscle growth.

As noted by Schoenfeld and colleagues in a 2021 paper:

“With respect to hypertrophy, the compelling body of literature indicates that similar whole muscle growth (i.e., muscle thickness, CSA) can be achieved across a wide spectrum of loading ranges ≥ ~30% 1RM.

2. Isometrics Show High EMG Readings

Isometric contractions (where the muscle contracts without changing length) tend to show higher EMG readings. Concentrics (where muscles shorten) are typically in second place, and eccentrics (where muscles lengthen) are in third place.

However, all three contractions play an essential role in fitness outcomes. If anything, the eccentric contraction is more valuable for muscle gain, as shown in some long-length partials research from the last couple of years.

3. Short Muscle Lengths Appear Better

EMG readings tend to peak as muscles shorten (such as near the top of a bicep curl), and electrical activity decreases as the muscle lengthens, even under load. 

But, again, we can’t say that the concentric is inherently more valuable than the eccentric.

4. Body Fat Percentage Can Be An Issue

Traditional EMG testing doesn’t involve skin penetration. Instead, electrodes are placed on the skin surface, which means they only measure surface EMG.

Aside from limiting data regarding actual muscle activity, this means people with a higher body fat percentage may show lower readings simply because the electrodes struggle to pick up activity due to the extra padding.

5. Electrode Placement Matters

Placing electrodes at the correct position on a muscle and far enough apart is crucial for limiting potential interference and getting the most accurate readings.

This means specialists conducting EMG research must be careful and experienced to get the most accurate data possible. While that is generally true, research is imperfect, and human error can skew the results, leading to wrong conclusions.

FAQ

1. Can EMG help assess muscle fatigue?

EMG readings can help measure muscle fatigue by showing decreased muscle activity. That said, this particular use case could be helpful in a lab setting, but it wouldn’t be practical when coaching athletes in the real world.

2. How can coaches interpret EMG data effectively?

As a coach, it’s best to consult with sports scientists or physiologists to interpret EMG data from experiments and research. The field is very nuanced, and it’s easy to draw incorrect conclusions.

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