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Does Controlling a Neuroprosthetic Require Movement?
  • Neuroengineering
  • Human
  • Grade 6+

Intention Without Movement – Isometric Contractions for Neuroprosthetics

Ever wondered if muscle signals can drive movement even when physical motion isn’t possible? This experiment reveals how EMG activity remains robust—even when a limb is restrained—and still controls the Human‑Human Interface (HHI).

Devices and Accessories3Related Experiments2

About the Experiment

What Will You Learn?

What Will You Learn?

  • Whether EMG persists even without visible muscle movement.
  • How the HHI converts EMG into action in another person.
  • The difference between neural drive (intent) and mechanical movement.
Background

Background

Muscles usually contract and move, producing both EMG and motion. But if you block movement, does the muscle still fire (EMG)? Using the Human‑Human Interface, you’ll find out how these hidden signals change, all while controlling another person—the Minion.

Procedure

  1. Safety First:

    Both volunteers must understand the procedure and agree to take part. The Minion must not take part with a pacemaker or other implanted electronic device, metal implants, epilepsy, a heart condition, or pregnancy. Turn the HHI off before attaching, moving or removing stimulation electrodes; start at the lowest intensity and raise it slowly; stop at once if it hurts or either volunteer asks. Keep both stimulation electrodes on one forearm—never across the chest, throat, neck or head.

  2. Equipment Setup:

    1. Attach electrode patches to the Controller’s forearm and connect to the Human-Human Interface.
    2. Connect the stimulation electrodes to the Minion.
    3. Verify an EMG signal from the Controller causes the minion to flex.

  3. Baseline Recording:

    1. Record baseline EMG from the Controller during normal contractions that cause the Minion to flex.

  4. Introducing Restraint:

    1. Gently restrain the Controller’s hand so it cannot move.
    2. Record EMG again, only now the controller will attempt to move the arm, but is being prevented from doing so.
    Introducing Restraint:

  5. Data Collection:

    1. Compare EMG strength and Minion movement between free and restrained conditions.
Results & Analysis

Results & Analysis

Do EMG bursts show up even if the arm is not moving? Did the Minion still respond? How did the two conditions compare in terms of EMG power? Can you channel the brain’s intent‑to‑move signal independently of actual movement to power neuroprosthetics? How does the information flow? Is it affected?

Draw the pathway from the Controller’s motor cortex to the forearm muscle and on through the HHI to the Minion, and mark where the restraint stops the movement but not the signal.

Design Challenge

  1. Control Without Movement

    Some people who would use a neuroprosthetic can still tense their muscles but cannot move their hand—for example, after losing a hand. Can you design a setup that lets a Controller with a restrained hand move the Minion every time?

    1. Rank your criteria: the Minion responds on 5 of 5 attempts, the EMG signal is strong, and both volunteers are comfortable. Either volunteer can call stop at any time.
    2. With the Controller’s hand gently restrained, test at least three electrode placements on the forearm. For each, record the EMG strength and how many of 5 attempts moved the Minion.
    3. Compare your designs in a table, combine the best features into one final setup, and test it again.
    4. Explain your trade-offs: which criterion did you favor, and what did it cost you?
    5. Judge your final setup for a real user who cannot move their hand: what would it cost, could they put it on alone, and is it safe to wear all day?

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.

    The nervous system's command reaches the muscle even when no movement results.

  • 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 muscle to the Minion and mark where the restraint stops the movement but not the signal.

  • MS-ETS1-2 Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

    Score at least three electrode placements against ranked criteria in one table (design challenge).

  • MS-ETS1-3 Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.

    Test at least three electrode placements on a restrained hand, compare the Minion's responses in a table, and combine the best features (design challenge).

  • HS-ETS1-3 Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics, as well as possible social, cultural, and environmental impacts.

    Rank reliability, signal strength and comfort, explain the trade-offs, and judge the setup for a user who cannot move their hand (design challenge).

Science and engineering practices

  • 1 Asking Questions and Defining Problems

    Define the problem: a control signal for someone who can tense their muscles but cannot move their hand (design challenge).

  • 2 Developing and Using Models

    Draw the pathway from the Controller's motor cortex to the Minion and mark where the restraint stops the movement but not the signal.

  • 3 Planning and Carrying Out Investigations

    Record EMG and the Minion's movement with the Controller's hand free and restrained.

  • 4 Analyzing and Interpreting Data

    Compare EMG strength and the Minion's response between the two conditions.

  • 6 Constructing Explanations and Designing Solutions

    Design a final setup from the test data and explain it (design challenge).

Crosscutting concepts

  • Cause and Effect

    The intent to move produces EMG even without movement.

  • Systems and System Models

    Controller, device and Minion form one loop.

  • Influence of Science, Engineering, and Technology on Society and the Natural World Engineering connection

    Neuroprosthetics for people who can tense their muscles but cannot move their hand depend on this signal.

Disciplinary core ideas

  • LS1.D Information Processing

    The brain's command to move travels to the muscle.

  • ETS1.B Developing Possible Solutions

    Test several solutions and weigh reliability against comfort.

  • ETS1.C Optimizing the Design Solution

    Use test results to pick and combine the best design.

Backyard Brains mapping using the book's method. Not in the book. Engineering claims rest on the design challenge on this page (Greg, 2026-10-06; real-user judgment step added 2026-10-08), modelled on the SpikerBot curriculum.