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Electromyography (EMG) of Agonist/Antagonist Muscle Pairs

Learn about the relationships between agonist and antagonist muscle pairs and how they function together for balance, posture, and smooth movements.

What Will You Learn?

  • Understand agonist and antagonist muscle relationships.
  • How the motor cortex sends electrical signals to control movement.
  • Learn about flexor and extensor muscles.
  • How to record and analyze muscle action potentials using the Human SpikerBox.

Background

The brain is the command center of the body, sending signals down through the spinal cord and nerves to control all of our muscles. Every time you move your hand, run, or even stand still, the brain coordinates countless commands to ensure your muscles work in harmony.

But how does the brain ensure these movements are smooth and precise rather than clumsy and chaotic? How does the brain communicate with and coordinate muscles to produce graceful movements? Can we uncover the mechanism behind this intricate process?

Procedure

In this experiment, you will explore how muscles work in pairs to produce coordinated movement. Using the Human SpikerBox, you’ll record the electrical signals generated by arm muscles as they contract and relax during common movements like waving or doing push-ups. These signals, called electromyograms (EMGs), will help you understand the relationship between agonist and antagonist muscles.

To get started, you’ll need the following materials Human SpikerBox, EMG electrodes, and a laptop, tablet, or smartphone for data recording. You will also need to identify the two muscles in your arm.

Look at your arm and locate the biceps (the muscle on the front of your upper arm) and the triceps (the muscle on the back of your upper arm). The biceps are responsible for flexing the arm, while the triceps extend it. Knowing their roles will help you understand the signals you’ll record.

Attach two sticker electrodes to your biceps, spaced about 2–3 inches apart. These will pick up the electrical activity of the muscle between the 2 locations.

Attach two more sticker electrodes to your triceps in a similar configuration.

Place a final sticker electrode on the back of your hand or wrist to act as a ground for both sets of muscles. You can clip both black wires to the same electrode.

Connect your Human SpikerBox to your device using the USB cable.

Open the SpikeRecorder app and verify that the SpikerBox is paired. Adjust the gain dial on the SpikerBox or in the app to ensure a clear signal.

Results & Analysis

Now that you’ve set up your electrodes and recorded EMG signals, it’s time to analyze your data and investigate how your muscles work together during different movements. Use the following steps and questions to guide your analysis:

Waving: Begin by waving to someone nearby. Can you identify which muscles (biceps or triceps) are active during this motion Hypothesize which muscle acts as the agonist and which as the antagonist at different points in the wave. If your EMG signals aren’t clear, adjust the placement of your electrodes to get stronger action potential readings. What changes improve the clarity of your data? Document your setup and findings as you adjust.

Explore Antagonist Muscle Activity: Notice whether the antagonist muscle shows any activity during your movements. What might cause spikes in the antagonist muscle Experiment with your arm motions and try to completely relax the antagonist muscle. What do you observe?

Push-Ups: Perform a push-up (or a modified version, such as against a sturdy table). Can you determine which muscle is the agonist as you lower yourself versus as you push back up? Does the role of the agonist switch, or does it remain constant during this exercise?