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Electromyography (EMG): Hear and See Muscles in Action
  • Human
  • Grade 4+

Electromyography (EMG) of Motor Movements

How does your brain make your body move? This experiment dives into the fascinating world of motor control, showing how neurons in your motor cortex communicate with muscles to generate movement. Let’s explore the electrical signals behind every step, jump, and dance!

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About the Experiment

What Will You Learn?

What Will You Learn?

  • How the motor cortex sends electrical signals to control movement.
  • How to record and compare surface muscle electrical activity using a SpikerBox.
  • What surface EMG can and cannot tell you about motor-unit activity and force.
Background

Background

Movement lets us explore the world, but how does your brain tell your body what to do? Motor pathways connect the brain and spinal cord to motor neurons that activate muscle fibers. In this experiment, you record the combined electrical activity of muscle fibers through the skin. The electrodes do not directly record the motor cortex or a single motor neuron, and EMG alone does not measure muscle force.

Experiment

  1. Biceps EMG Recording

    Biceps EMG Recording

    Materials:

    • Human SpikerBox (or Muscle SpikerBox)
    • Orange electrode cable
    • Patch electrodes (3)
    • Smartphone, tablet, or computer with SpikeRecorder

    Setup:

    • Place two patch electrodes on your biceps, spaced a few centimeters apart but over the same muscle.
    • Attach the red recording clips to the patch electrodes. Clip the black ground lead to the third patch electrode on the back of your hand.
    • Connect the orange cable to the SpikerBox and power it on.
    • Launch SpikeRecorder and confirm the device is recognized.

    Procedure:

    • Relax your arm and record a 10-second baseline.
    • Slowly flex your biceps. Listen for changes in the sound of muscle activity and watch the trace on the screen.
    • Hold the contraction for 5 seconds, then relax.
    • Repeat the flex-and-relax cycle five times, logging the data for later analysis.
Results & Analysis

Results & Analysis

Compare the recording during relaxation and each contraction. Use equal-duration intervals and the same channel settings to compare RMS amplitude. Keep repeat observations and note movement artifacts. Surface EMG contains overlapping activity from many fibers: counting visible peaks does not give an individual motor unit’s firing rate, and a change in RMS does not independently identify recruitment or measure force.

Draw the pathway from your motor cortex to your biceps (motor cortex, spinal cord, motor neuron, muscle fibers) and label where your electrodes recorded.

NGSS alignment

Performance expectations

  • MS-LS1-3 Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

    Nerve signals and muscle fibers work together as subsystems to produce force.

  • HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

    Draw the pathway from motor cortex to biceps: brain, spinal cord, motor neurons and muscle fibers working as one system.

Science and engineering practices

  • 2 Developing and Using Models

    Draw the pathway from your motor cortex to your biceps and label where you recorded.

  • 3 Planning and Carrying Out Investigations

    Record a baseline and five flex-and-relax cycles from the biceps.

  • 4 Analyzing and Interpreting Data

    Compare spike shapes during contraction and relaxation, measure spike widths, and plot spike frequency against flex strength.

  • 6 Constructing Explanations and Designing Solutions

    Use your frequency-versus-strength plot to explain how recruiting more motor units, and firing them faster, scales force.

Crosscutting concepts

  • Cause and Effect

    A stronger flex brings more spikes.

  • Structure and Function

    Muscle spikes are broader than nerve spikes.

Disciplinary core ideas

  • LS1.A Structure and Function

    Motor units: a motor neuron and the muscle fibers it drives.

  • LS1.D Information Processing

    Motor commands travel from brain to muscle.

Backyard Brains mapping using the book's method. Not in the book.

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